Earth 2 Midterm 2

Identify the FALSE statement. Internal differentiation Select one: a. "stirred" Earth's interior and thus hastened Earth's cooling. b. happened just before Earth's collision with a protoplanet that blasted away moon material. c. involved heavy molten iron sinking to Earth's center to become its core. d. is the process that resulted in Earth's interior having different materials at different depths.

- "stirred" Earth's interior and thus hastened Earth's cooling. - The process of internal differentiation generated enough heat to make Earth even hotter.

What is the pH of rainwater? (iclicker)

- <7 - <7 = acid

Identify the FALSE statement. Select one: a. Geologists generally agree that plate tectonics activity began in the Archean Eon. b. About 80% of Earth's continental crust existed by the end of the Hadean Eon. c. There was intense meteorite bombardment of Earth about 4 Ga that destroyed Earth's earliest crustal rock. d. The Moon formed from a collision between Earth and a large protoplanet.

- About 80% of Earth's continental crust existed by the end of the Hadean Eon.

Which of the following is not an environment where shale would form? (iclicker) A. Lakes B. River flood plains C. Deep ocean D. Alluvial fans E. Lagoons

- Alluvial fans

Which of the following statements is FALSE? Select one: a. Varieties of an element that differ only in the number of neutrons are called isotopes. b. The generally accepted age of Earth is 4.54 billion years. c. An unconformity is a break in the rock record that indicates the area was underwater for millions of years. d. A formation is the name of a rock layer identified by such factors as rock type and approximate geologic age.

- An unconformity is a break in the rock record that indicates the area was underwater for millions of years. - on the contrary, being underwater would be an excellent environment for deposition

Which geologic time interval saw the first continents, the first life, and possibly the first cratons?

- Archean - By the Archean, Earth had cooled enough from Hadean times to allow its surface to freeze and form continents, cratons, and plates, and contain ocean waters. Proterozoic means "first life," but it's a misnomer; life began in Archean times.

Choose the proper listing of names to fit the following three descriptions- Age of Mammals, Age of Dinosaurs, and longest geologic time period. Select one: a. Mesozoic, Cenozoic, Paleozoic b. Cenozoic, Mesozoic, Precambrian c. Mesozoic, Cenozoic, Proterozoic d. Cenozoic, Hadean, Paleozoic

- Cenozoic, Mesozoic, Precambrian - Mammals were the dominant life-form during the Cenozoic, and dinosaurs were dominant during the Mesozoic; the Precambrian represents more than seven-eighths of all Earth history.

Which statement is FALSE? Select one: a. Dolostone and limestone are polymorphs—they have the same chemical composition. b. Both chert and limestone may have either chemical or biochemical origin. c. Chemical sedimentary rocks are crystalline in texture. d. Gypsum and halite are evaporite minerals.

- Dolostone and limestone are polymorphs—they have the same chemical composition. - Dolostone and limestone do not have the same chemical composition—limestone is made of the mineral calcite (CaCO3), while dolostone is made of the mineral dolomite (CaMg[CO3]2).

- Recalling Bowen's reaction series, which types of plutons are likely to create the highest T aureoles? (iclicker)

- Gabbro

Which of the following statements is FALSE? Select one: a. Human ancestors first appeared in the late Mesozoic. b. The human genus Homo first appeared around 2.8 million years ago. c. Fossils of modern humans (Homo sapiens) date back to about 200,000 years ago. d. The Cenozoic is known as the Age of Mammals.

- Human ancestors first appeared in the late Mesozoic.

The first feathered birds appeared in the

- Jurassic - The first feathered bird, called Archaeopteryx, didn't appear until the Jurassic period of the Mesozoic Era.

Which of the following is NOT one of the smaller continents formed by the breakup of Pannotia? Select one: a. Siberia b. Laramide c. Baltica d. Laurentia

- Laramide: this is the late Mesozoic/early Cenozoic orogeny that resulted in the Rocky Mountains.

Which of the following is not true about clast/grain size in a sedimentary rock: (iclicker) A. Larger clasts are always rounded due to abrasion during transport B. Larger clasts are deposited cloer to the source of the sediment C. Smaller grain sizes are indicative of low energy depositional environments D. Larger clasts are indicative of high energy depositional environments E. Smaller grains are transported greater distances than larger grains

- Larger clasts are always rounded due to abrasion during transport

The continents that comprised Pangaea began to split apart during the

- Late Triassic/Early Jurassic

Identify the appropriate time period where vascular plants with woody tissues, seeds, and veins shared the land with spiders, scorpions, insects, and crustaceans, while jawed fish cruised the oceans and the first amphibians left water to visit land. a. Early Mesozoic. b. Late Mesozoic. c. Early Cenozoic. d. Middle Paleozoic. e. Middle Proterozoic

- Middle Paleozoic

Protoliths of Metamorphic Rocks

- Pelitic: slate, phyllite, schist, gneiss, migmatite; generally foliated - Mafic: greenstone, amphibolite, granulite, eclogite; may or many not be foliated - Carbonate(limestone, dolostone): forms marble - Ultramafic(peridotite): serpentinite, generally not foliated

Which of the following shows the four time divisions listed from oldest to youngest?

- Precambrian, Paleozoic, Mesozoic, Cenozoic

Which of the following has nothing to do with fossils of early life? Select one: a. Rodinia b. stromatolites c. cyanobacteria d. Ediacaran fauna

- Rodinia - Rodinia is the name of the first supercontinent known, existing back in the Proterozoic eon. Stromatolites are mats of cyanobacteria, which are simple prokaryotic cells; Ediacaran fauna are early multicellular invertebrates found in Australia.

Which of the following statements is FALSE? Select one: a. The "radiometric clock" starts when a radioactive mineral cools below its closure temperature. b. Isotopic dating relies on the parent-daughter ratio. c. Scientists can date any radioactive material back only three half-lives; after this there's not enough parent material left to measure. d. Carbon-14 dating is used to date organisms, not minerals.

- Scientists can date any radioactive material back only three half-lives; after this there's not enough parent material left to measure. - After three half-lives, there's still one-eighth of the radioactive parent material left, which is easily detected. Carbon-14 can be detected for about 12 half-life periods (about 70,000 years).

Which of the following is TRUE? Select one: a. Specifying the age of one feature with respect to another is called its relative age. b. Saying that a fossil is 4 million years old reports its relative age. c. Geologists learned how to determine numerical age long before they could determine relative age. d. Specifying the date on which an event took place is an example of relative age.

- Specifying the age of one feature with respect to another is called its relative age. - Relative age dating provides the age of a feature or event with respect to another feature or event in the same sequence.

A corpse with flesh intact, found in the Alps in 1991, was dated by the carbon-14 method and showed a parent-daughter isotope ratio of approximately 1:1, with slightly more parent material than daughter material. The half-life of carbon-14 is 5,730 years. Which of the following statements is TRUE? Select one: a. The age could logically be 5,300 years. b. The age could logically be 6,000 years. c. Since the body was still organic and had not been petrified, it was inappropriate to use the carbon-14 process. d. The age could logically be 6,730 years.

- The age could logically be 5,300 years. - Since there was still more parent material than daughter, one half-life had not quite been reached. The carbon-14 method is used on organic material not rock.

An area of slightly dipping clastic sedimentary rock layers, which show graded bedding with the finest materials at the top of each graded bed, has large inclusions and is intruded by an igneous dike. Apply the basic principles for determining relative ages and identify the FALSE statement. Select one: a. The dike is older than the sedimentary rock layers it cuts across. b. The sedimentary layers started out lying flat. c. The oldest sedimentary layer is the bottom layer. d. The igneous intrusion "baked" (metamorphosed) the sedimentary rock it touched.

- The dike is older than the sedimentary rock layers it cuts across - The dike must be younger than the sedimentary rock layers that it cuts across because the rock layers need to be there before they can be cut by the intrusion.

Which of the following has nothing to do with the K-T (Cretaceous-Tertiary) boundary? Select one: a. Chicxulub b. iridium c. a meteorite impact d. glass spheres formed by sudden melting then freezing of rock e. Thomas Huxley

- Thomas Huxley - Huxley was a 19th-century geologist who realized Earth had changed immensely over time; Walter and Luis Alvarez were the scientists who analyzed the K-T boundary layer clay. Iridium is a heavy element found only in extraterrestrial objects; glass spheres are produced after rock is melted then cooled after impact; Chicxulub is the impact site; a 13-km wide meteorite was the cause of the catastrophe.

The structure that may form where a stream enters a lake is called Select one: a. till. b. a sedimentary basin. c. a turbidite. d. an alluvial fan. e. a delta.

- a delta - Till forms from glacial melt, alluvial fans form when rivers exit mountains, and a sedimentary basin is a tectonic feature that has nothing to do with streams entering lakes. A turbidite forms by an underwater avalanche.

Theoretically, "snowball Earth" conditions of the late Proterozoic Eon would have persisted forever were it not for greenhouse warming caused by volcanically derived

- carbon dioxide - Carbon dioxide is a greenhouse gas, which brought Earth out of the snowball conditions of the Proterozoic era

Because the velocity of sediment settling (deposition) is positively related to grain size for waterborne sediments, fluvial deposits are more likely than glacial deposits to:

- be well sorted

Why is rainwater acidic? (iclicker)

- because of sulfur and nitrogen emitted by coal fire power plants - because there is CO2 in the atmosphere

Rocks formed dominantly from the calcium carbonate shells of marine organisms are classified as _____ and called _____.

- biochemical; limestone - Biochemical limestones are made from the calcium carbonate shells of marine organisms.

Identify the FALSE statement. Radiometric dating Select one: a. can be used only if there is some uranium present in the rock. b. of sedimentary rock dates the time of crystallization of the sedimentary minerals, not the time of sedimentary rock formation. c. can begin only when the rock cools enough to lock the isotopes into the crystal lattice. d. of metamorphic rock tells when the high temperatures of metamorphism cooled below the closure temperatures of the minerals involved.

- can be used only if there is some uranium present in the rock.

Which of the following rock types does not contain the mineral calcite? Select one: a. chert b. chalk c. fossiliferous limestone d. micrite

- chert - Chert is composed of the mineral quartz (i.e., it is siliceous). The others are examples of biochemical limestone, all composed of the mineral calcite or its polymorph aragonite.

Lithification, the process by which sediments are turned into sedimentary rocks, includes

- compaction and cementation

The boundary surface between two stratigraphic formations is called a

- contact

Identify the FALSE statement. During the Pleistocene Ice Age Select one: a. a continental land bridge west of Alaska was exposed and allowed migration of animals and people from Asia to North America. b. sea level fell because water was tied up as ice. c. continental glaciers in the northern hemisphere advanced and retreated at least 20 times. d. continental glaciers covered all of North America.

- continental glaciers covered all of North America. - The glaciers extended just a little south of the United States-Canadian border. New York City was under ice.

Which of the following is NOT a method to determine numerical age? Select one: a. carbon-14 dating b. radioactive decay of uranium to lead c. analyzing growth ring patterns in trees d. cross-cutting relations

- cross-cutting relations

Why might there be melting in continent-continent collision zone? collisions

- crustal radioactivity

Ripple marks, dunes, and cross bedding are useful indicators of

- current direction - Moving wind or water creates ripples, dunes, and cross beds in sediments. Each has a distinctive shape or pattern that can be used to infer current direction.

Which of the following accurately ranks the subdivisions of geologic time in order from largest to smallest?

- eon, era, period, epoch

Which of the following is not an agent of erosion? (iclicker)

- fire

Why might there be volcanism in the Altiplano?

- fluids released from the subducted slab cause melting - crustal radioactivity

Which of the following is NOT used to identify metamorphic rocks? A. Fossils B. Mineral assemblage C. Texture D. Foliation E. Light-dark color bands

- fossils

Banded-iron formations (BIFs) formed

- in the Proterozoic deep ocean. - Banded iron formations precipitated out of seawater when the oceans became oxygenated and could no longer contain large quantities of dissolved iron.

Which of the following statements is FALSE? The principle of Select one: a. original continuity says sedimentary layers began as continuous expanses of sediment. b. superposition says in a sequence of sedimentary beds, the youngest is on top. c. cross-cutting relations says the feature doing the cutting is younger than the feature it cuts. d. inclusions says rock containing inclusions is older than the inclusions.

- inclusions says rock containing inclusions is older than the inclusions. - The principle of inclusions states that the inclusions are OLDER than the surrounding rock.

The Paleozoic Era ended with the largest mass extinction event that ever occurred. Which of the following is hypothesized to be the cause of that extinction?

- intense volcanic activity in Siberia - the late-Paleozoic (Permain Period) extinction was most likely due to intense volcanic activity in the region that is now Siberia.

Uniformitarianism (from quiz)

- is illustrated by scientists' seeing pillow lava form only underwater, then theorizing that pillow lava found high in the mountains today did nevertheless form underwater - Features of the Earth are constantly changing, and catastrophic events still happen. The present is a key to the past and to the future, so since pillow lava forms underwater today, it must have done so in the past.

Geologists estimate that the age of the Earth is 4.54 billion years old, based on

- isotopic dating of meteorites thought to be from primitive solids of the early Solar System. - Geologists assume all objects in the Solar System developed at roughly the same time; therefore the age of differentiated meteorites should represent the age at which the Earth formed.

Gymnosperms (naked-seed plants like conifers) were widespread in the late Paleozoic, but angiosperms (flowering plants) gained dominance in the

- late Mesozoic - Plants are classified as gymnosperms if they release their seeds from cones, and they are more primitive than angiosperms, which retain their seeds within the protective shelter of flower parts. Angiosperms (flowering plants) gained dominance over conifers in the late Mesozoic.

Which of the following sedimentary features is the surest indicator that the past environment was subaerial (under air), not submarine (underwater)? Select one: a. fossil marine clam shell imprints b. mud cracks c. ripple marks d. scour marks e. turbidites

- mud cracks - Mud cracks develop only if a muddy surface dries up sufficiently to crack into roughly hexagonal plates. Turbidites are submarine avalanche deposits. Scour marks are small troughs scooped out by current flowing over a sediment surface. Fossil marine clam shell imprints certainly indicate a marine (not terrestrial) environment.

Which of the following features is a bed-surface marker, meaning it appears on the surface of a bed due to events during or soon after sediment deposition?

- mud cracks - Mud cracks form on a bed surface after a mud layer dries up after deposition.

What type of unconformity forms when sedimentary rocks overlie either igneous or metamorphic rocks? Select one: a. nonconformity b. angular unconformity c. disconformity d. baked contact

- nonconformity - This is the definition of a nonconformity. A disconformity is a surface between parallel sedimentary beds of significantly different ages; an angular unconformity occurs when flat lying sedimentary layers overlie tilted layers; and baked contacts are formed when igneous intrusions create contact metamorphism (a baked zone) around the intruding magma.

Identify the FALSE statement. William Smith's observations Select one: a. were made around 1800 in fresh exposures of sedimentary bedrock in the English countryside. b. recognized that groups of fossil species (fossil assemblages) occurred in limited intervals of strata. c. noted that a fossil species could disappear then reappear in much younger strata. d. lead to the principle of fossil succession.

- noted that a fossil species could disappear then reappear in much younger strata. - Once a fossil species disappeared, it did not reappear. Extinction is forever.

The organic sedimentary rock that is composed of mud-sized particles and partially decayed organic matter (kerogen) derived from plankton and algae remains is Select one: a. anthracite. b. oil shale. c. coal. d. fossiliferous limestone. e. chert

- oil shale - Coal is partially decayed particles, larger than mud-sized, and derived from swamp plants, not plankton and algae; the other rocks are not composed of decayed organic matter.

Which of the following was NOT a component of Earth's Hadean atmosphere? Select one: a. methane b. hydrogen c. oxygen d. ammonia

- oxygen - Atmospheric oxygen didn't accumulate until the Proterozoic Eon, 2.5 Ga to 543 Ma. Other gases in the Hadean atmosphere were water, carbon dioxide, and sulfur dioxide.

Which of the following statements is FALSE? The first life forms Select one: a. likely evolved around submarine vents, called black smokers. b. date back to between 3.5 and 3.8 billion years. c. may have been simple cells of bacteria and cyanobacteria (blue-green algae). d. probably occurred in oxygen-rich, shallow, sun-lit ocean waters.

- probably occurred in oxygen-rich, shallow, sun-lit ocean waters. -Oxygen-rich atmosphere (or oceans) didn't exist when the earliest life forms began, and the ability to extract energy from sunlight didn't evolve until much later. First life probably occurred in black smokers along mid-ocean ridges between 3.5 and 3.8 Ga.

What is the most logical ancient environment to have produced a deposit consisting of layers of well-sorted sandstone with cross beds several meters high? Select one: a. alluvial fan along a mountain front b. shallow-water carbonate area c. sand dunes d. glacial valley e. rivers

- sand dunes - Alluvial fans would produce conglomerates, carbonate areas would be limestone, and glacial valleys would contain unsorted till. Only sand dunes would produce well-sorted sandstone with cross bedding.

Formation of a clastic sedimentary rock involves five stages. Which of the following describes erosion?

- separation of rock or regolith from its substrate - Erosion is described as the combination of processes that separate rock (or surface debris) from its substrate and involves abrasion, falling, scouring, etc., and is caused by moving air, water, or ice.

A clastic sedimentary rock with clay- and silt-sized grains that breaks in thin sheets is called Select one: a. siltsone. b. arenite. c. wacke. d. mudstone. e. shale.

- shale - Only mudstone and shale are rock made of silt- and clay-sized pieces, but a mudstone doesn't break into thin sheets.

As sediment is transported downstream, away from its point of origin, the particles become

- smaller - Clastic sediments increase in maturity as they are transported farther from their point of origin. Along the way, they become smaller, increasingly well-rounded, and well-sorted, and easily weathered grains (like feldspar) are gradually destroyed.

As compared with metamorphism, diagenesis:

- takes place at lower temperatures and pressures

If you equate all Earth history to one calendar year, the history of our species (Homo sapiens) would occupy

- the last hour before midnight on New Year's Eve. - Human history (the history of our human species, Homo sapiens) represents an incredibly small portion of Earth history, equivalent to the last hour before midnight if all of Earth history were equated to one calendar year.

The Cenozoic Era: The Modern World Comes to Be

- the final stages of the Pangaea breakup separated Australia from Antarctica and Greenland from North America, and formed the North Sea between Britain and continental Europe - the Atlantic Ocean continued to grow due to sea-floor spreading on the Mid-Atlantic Ridge - collisions of the former Gondwana continents with the southern margins of Europe and Asia resulted in the formation of the largest orogenic belt on Earth today, the Alpine-Himalayan chain - in South America, convergent-boundary activity built the Andes, which remains an active orogen to the present day - in North America, convergent-boundary activity continued without interruption until about 40Ma (the Eocene Epoch), yielding the Laramide orogeny - because of the rearrangement of plates off the western shore of North America, a transform boundary replaced the convergent boundary in the western part of the continent by 25 Ma - volcanoes and compression ceased in western North America, and the San Andreas Fault system formed along the coast of the United States, and the Queen Charlotte Fault system developed off the coast of Canada - Basin and Range Province: a broad continental rift whose development has stretched the region to twice its original width; contains long, narrow mountain ranges separated from each other by flat, sediment filled basins - during the Cenozoic Era, the global climate rapidly became cooler, and by the early Oligocene Epoch(~34 Ma), Antarctic glaciers reappeared for the first time since the Triassic - about 2.5 Ma, the Isthimus of Panama formed, separating the Atlantic completely from the Pacific, changing the configuration of oceanic currents, perhaps leading the Arctic Ocean to freeze over - Pleistocene Ice Age: during the overall cold climate of the past 2 million years, continental glaciers have expanded and retreated across northern continents at least 20 times - about 11,000 years ago, the climate warmed, and we entered the interglacial time interval we are still experiencing today - plant life recovered, and soon forests of both angiosperms and gymnosperms grew - the grasses, which first appeared in the Cretaceous, spread across the plains in temperate and subtropical climates by the middle of the Cenozoic Era - dinosaurs, not including birds, were extinct - mammals rapidly diversified, Cenozoic Era nicknamed the Age of Mammals - during the latter part of the era, huge mammal appeared (such as mammoths, giant beavers, giant bears, giant sloths), but these became extinct during the past 10,000 years, probably because of hunting by humans - ape-like primates diversified in the Miocene Epoch (about 20 Ma), and the first human-like primate appeared at about 4 Ma, followed by the first members of the human genus, Homo, at about 2.4 Ma - fossil evidence, primarily from Africa, indicates that Homo erectus, capable of making stone axes, appeared about 1.6 Ma, and Homo neanderthalensis (Neanderthal man) appeared about 500,000 and led to our species, Homo sapiens - modern people appeared about 200,000 years ago, and the last Neanderthals and Denisovans died off over 25,000 years ago

Identify the FALSE statement. There is very little rock record for Earth's first 600 million years because Select one: a. any rock that formed during that time was likely melted/recycled. b. rocks of that age sank back down into the Earth. c. the surface then was one huge ocean basin filled with hot water and nothing else. d. intense meteorite bombardment may have destroyed most land surface.

- the surface then was one huge ocean basin filled with hot water and nothing else. - The surface was probably too hot and suffering intense meteorite bombardment during the first few hundred million years, preventing the formation of large oceans. At that time, the surface of Earth was probably a magma ocean with very little permanent rock, if any. Any rock that had formed prior to ~4.0 Ga sank back down into the Earth, melted, and was recycled.

If water is the transport mechanism of sediment, the grain size of sedimentary deposits most closely indicates the:

- velocity of the water at the moment the sediment settled to the bottom

Volcanoes can influence climate because

- they send ash to the statosphere that blocks sunlight, thereby cooling Earth's surface -they add CO2 to the atmosphere, which is a greenhouse gas and warms Earth's surface

Biochemical Sedimentary Rocks(consists of shells): Limestone(biochemical)

- clams, oysters, snails(gastropods), plankton, lampshells(brachiopods), and other organisms make solid shells of calcium carbonate - when the organisms die, the shells remain and may accumulate, forming the biochemical version of limestone - fossiliferous limestone: consists of visible fossil shells or shell fragments - micrite: consists of very fine carbonate mud - chalk: consists of plankton shells - water passing through the rock not only precipitates cement but also dissolves some carbonate grains and causes new ones to grow

Volcanoes & Climate

- 1815: Tambora eruption - "year without a summer" - tiny particles of ash reach stratosphere - SO2 aerosols injected into stratosphere - above the 'weather' so it didn't rain out - circled the globe in ~2 weeks - June snow in New England - widespread crop failure - In addition to Tambora, global cooling caused by the following: - Krakatau, Indonesia 1883 - Pinatubo, Philippines 1991

Eruption of Mt. Ontake, Japan September 27, 2014

- 57 people killed by phreatic eruption

According to the metamorphic facies graph (Box 7.1 in your text), which of the following statements is TRUE? Select one: a. Greenschist facies rocks form at depths greater than 35 km. b. Hornfels facies rocks form in a narrow range of temperature conditions (<400˚C). c. Blueschist facies rocks form at high pressures and low temperatures. d. The highest pressure facies indicated on this graph is the hornfels facies.

- Blueschist facies rocks form at high pressures and low temperatures. - Blueschist facies rocks do form under high pressure but low temperature conditions. However, hornfels facies rocks form under a wide range of temperatures, greenschist facies form at depths less than ~35 km, and the highest pressure facies on this diagram is the eclogite facies.

The Late Mesozoic Era (Cretaceous Period 145-65 Ma)

- Earth's climate continued to shift to warmer conditions, and sea level rose significantly, reaching levels that had not been attained for the previous 200 million years - great seaways flooded most of the continents - the breakup of Pangaea continued, with the opening of the South Atlantic Ocean and the separation of South America and Africa from Antarctica and Australia - India broke away from Gondwana and headed rapidly northward toward Asia - at the end of the Cretaceous, continued compression along the convergent boundary of western North America caused slip on large faults in the region of Wyoming, Colorado, eastern Utah, and northern Arizona - these faults penetrated deep into the Pre-cambrian rocks of the continent, and thus movement on them generated basement uplifts - overlying layers of Paleozoic strata warped into large monoclines, folds whose shape resembles the drape of a carpet over a step - this event, called the Laramide orogeny, formed the structure of the present Rocky Mountains in the United States - sea-floor spreading rates may have been up to 3 times faster during the Cretaceous than they are today - oceanic crust was younger and warmer and Cretaceous mid-ocean ridges occupied more volume; the extra volume displaced sea water, causing sea level to rise - huge submarine plateaus formed from basalts erupted at hot-spot volcanoes, which implies that particularly active mantle plumes, or superplumes, reached the base of the lithosphere - volcanism associated with extra-rapid sea floor spreading likely released CO2 into the atmosphere, which led to a global rise in atmospheric temperature, causing sea water to expand and polar ice sheets to melt; sea levels rose even higher and the continents flooded and large epicontinental seas formed - in the late Mesozoic, modern fish appeared and became dominant - the new fish had short jaws, rounded scales, symmetrical tails, and specialized fins - huge swimming reptiles and gigantic turtles (with shells up to 4 m across) preyed on fish - cycads largely vanished, and angiosperms (flowering plants), including hardwood trees, began to compete successfully with conifers for dominance of the forest - dinosaurs dominated and inhabited almost all environments on Earth - Tyrannosaurus rex was a Cretaceous dinosaur - Pterosaurs, with wingspans of up to 11m, soared overhead, and birds began to diversify - mammals diversified and developed larger brains and more specialized teeth, but remained small and rat-like - The "K-T boundary event" was a sudden mass extinction of most species on Earth - the dinosaurs, which had ruled the planet for over 150 million years, vanished, along with 90% of plankton species in the ocean and up to 75% of plant species - the discovery of high concentrations of iridium in shale deposits as well as grains of coesite and carbon from burned vegetation pointed to the occurrence of a huge meteorite impact at the time of the K-T boundary - geologists found a 100km-diameter and 16 km deep meteorite crater buried beneath younger strata of the Yucatan Peninsula in Mexico - isotopic dating indicated that formation of the crater occurred 65 Ma, the time of the K-T boundary event - this crater was known as the Chicxulub crater - the impact blasted huge quantities of debris into the sky and probably also generated 2km high tsunamis and blasts of hot air that set forests on fire - due to so much debris in the atmosphere, there would have been perpetual night and winter-like cold for months after this event - chemicals ejected into the air could have combined with water to produce acid rain - these conditions would cause photosynthesis to cease, and thus break the food chain and trigger extinction

Terrestrial (Nonmarine) Sedimentary Environments

- Glacial environments: at the end of the glacier, where the ice finally melts away, the sediment that had been in or on the ice accumulates as "glacial till"; till is unsorted and unstratified - it contains clasts ranging from clay size to boulder size all mixed together - Mountain stream environments: fast-moving water can carry large clasts, even boulders and cobbles during a flood; when water flow slows, the largest clasts settle out to form gravel and boulder beds, while the stream carries finer sediments like sand and mud farther downstream; sedimentary deposits would include breccia and conglomerate - Alluvial-fan environments: in arid regions, where there is not enough water to flow continuously, the stream deposits its load of sediment near the mountain front, producing a wedge-shaped apron of gravel and sand called an alluvial fan; the sand here still contains feldspar grains; alluvial-fan sediments become arkose and conglomerate - Sand-dune environments: strong winds can move dust and sand, the dust gets carried away, and the resulting well-sorted sand can accumulate in dunes; there are thick layers of well-sorted sandstone, in which we can find large cross beds - River (fluvial) environments: river sediments lithify to form sandstone, siltstone, and shale; coarser sediments tumble along the bed in the river's channel and collect in cross-bedded, rippled layers while the finer sediments drift along and settle out along the banks of the river or on the floodplain(flat land on either side of the river) - Lake environments: any course sediment brought into the lake by a stream settles out at the stream's outlet, only fine clay makes it out into the center of the lake, where it settles to form mud on the lake bed; lake sediments typically consist of finely laminated shale - delta: a wedge of sediment that accumulates where moving water enters standing water; consist of three components: topset beds composed of gravel, foreset beds of gravel and sand, and silty bottomset beds

Types of Volcanic Products

- Lava flows, pyroclastic deposits, gases

California's Dormant Volcanoes

- Long Valley Caldera, Mammoth Lake -Giant eruption ~760,000 years ago to form Bishop Tuff -"The caldera has been showing unrest in recent years, in the form of deformation of the caldera floor and earthquake swarms. It contains numerous hot springs and fumaroles" - "Pyroclastic flows swept over an area of more than 2,200 km^2 and buried the pre-existing ground to depths of nearly 200m (660 ft) just south of the caldera."

Coastal and Marine Environments

- Marine delta deposits: river water stops flowing when it enters the sea, so sediment settles out; includes swamps, channels, floodplains, and submarine slopes, so deposits of an ocean-margin delta produce a great variety of sedimentary rock types; deeper-water sediments are buried by shallower-water sediments - Coastal beach sands: well-sorted, medium-grained sandstone, perhaps with ripple marks - Shallow-marine clastic deposits: clastic sedimentary layers that accumulate in this environment tend to be fine-grained, well-sorted, well-rounded silt, and are inhabited by a variety of organisms such as mollusks and worms - Shallow-water carbonate environments: beaches collect sand composed of shell fragments; lagoons(protected bodies of quiet water) are sites where carbonate mud accumulates; reefs consists of coral and coral debris; shallow-water carbonate environments transform into various kinds of limestone - Deep-marine deposits: clay settles out onto the deep-sea floor, forming deposits of finely laminated mud-stones, and plankton shells settle to form chalk(from calcite shells) or chert(from siliceous shells)

The Early and Middle Mesozoic Era (Triassic-Jurassic Periods, 251-145 Ma)

- Pangaea existed for about 100 million years until rifting commenced during the Late Triassic and Early Jurassic Periods and the supercontinent began to break up - by the end of the Jurassic Period, rifting had succeeded in splitting North America from Europe and Africa - the Mid-Atlantic Ridge formed, and the North Atlantic Ocean started to grow - Earth had an overall warm climate during the Triassic and Early Jurassic, but it cooled during the Late Jurassic and Early Cretaceous - by the Middle Jurassic Period, sea level began to rise, and a shallow sea submerged much of the Rocky Mountain region - beginning with Late Permian and continuing through Mesozoic time, subduction generated volcanic island arcs and caused them, along with microcontinents and hot-spot volcanoes, to collide with North America - thus, North America grew in land area by the accretion of crustal fragments on its western margin - these fragments are called exotic terranes, because they consist of crust that formed elsewhere, not originally on or adjacent to the continent - from the end of the Jurassic through the Cretaceous, a major continental volcanic arc, the Sierran arc, grew on the western margin of North America itself - reptiles swam in the oceans, and new kinds of corals became the predominant reef builders - on land, gymnosperms and reptiles diversified, and the Earth saw its first turtles and flying reptiles - at the end of the Triassic Period, the first true dinosaurs evolved - the legs of dinosaurs were positioned under their bodies rather than off to the sides(like reptiles), and they were possibly warm-blooded - by the end of the Jurassic Period, gigantic sauropod dinosaurs (weighing up to 100 tons), and other dinos such as stegosaurus, thundered across the landscape, and the first feathered birds, such as Archaepteryx, took to the skies - the earliest ancestors of mammals appeared at the end of the Triassic Period, in the form of small, rat-like creatures

Which of the following statements is TRUE? Select one: a. Pieces of broken rock are collectively called clasts or detritus. b. Conglomerates consist of large, angular clasts. c. A well-sorted clastic rock is made up of different-sized particles. d. All clastic sedimentary rocks are cemented (held together) by silica. e. All clastic sedimentary rocks are cemented (held together) by calcite.

- Pieces of broken rock are collectively called clasts or detritus - Conglomerates are made up of various grain sizes and the clasts are rounded, not angular; a well-sorted rock is made up of uniform particle sizes; and clastic rocks can be cemented by different types of cement, including calcite but also quartz.

Metamorphism

- the transformation of one rock to another under the influence of changing temperature, pressure and/or deformation - includes both recrystallization and the formation of new minerals

Forming metamorphic minerals and textures

- Recrystallization: changes the shape and size of grains without changing the identity of the mineral making up the grains - Phase change: transforms one mineral into another mineral with the same composition but a different crystal structure, involves the rearrangement of atoms - Metamorphic reaction, or neocrystallization: results in growth of new mineral crystals that differ from those of the protolith; during neocrystallization, chemical reactions digest minerals of the protolith to produce new minerals of the metamorphic rock - Pressure solution: mineral grains dissolve where their surfaces are pressed against other grains, producing ions that migrate through the water to precipitate elsewhere - Plastic deformation: when a rock is squeezed or sheared at elevated temperatures and pressures, grains behave like soft plastic and change without breaking

Which of the following statements about metamorphic rocks and their characteristic environments is TRUE? Select one: a. Slate, phyllite, schist, and gneiss are found in areas of continental collision. b. Mylonites are found along convergent plate boundaries where magma is rising. c. Gneiss is found in metamorphic aureoles surrounding plutons. d. Eclogites are found in contact aureoles. e. Blueschists are found in the mid-ocean ridge.

- Slate, phyllite, schist, and gneiss are found in areas of continental collision. - Gneiss, a foliated metamorphic rock, requires shearing stress to form; plutons do not cause shearing and they create nonfoliated rock. Mylonites form due to shearing stress along faults deep in the crust, not the heat of convergent boundaries. Blueschists form where there is extreme pressure and low heat, which does not describe mid-ocean ridge conditions.

Fossil Succession

- William Smith (1769-1839) - fossil assemblage: the group of fossil species - principle of fossil succession: in a stratigraphic sequence, different species of fossil organisms appear in a definite order; once a fossil species disappears in a sequence of strata, it never reappears higher in the sequence (extinction)

Metamorphic rock

- a rock that forms when a preexisting rock, or protolith, undergoes a solid-state change in response to the modification of its environment - metamorphic minerals: new minerals that grow in place within the solid rock only under metamorphic temperatures and pressures - metamorphic texture: defined by distinctive arrangements on mineral grains not found in other rock types - metamorphic foliation: parallel alignment of platy minerals (such as mica) and/or the presence of alternating light-colored and dark-colored layers

Diagenesis

- all the physical, chemical, and biological processes that transform sediment into sedimentary rock and that alter characteristics of sedimentary rock after the rock has formed - under higher pressures, pressures, and contact with warm groundwater, diagenesis can cause chemical reactions in the rock that produce new minerals and can also cause cement to dissolve or precipitate - as temperature and pressure increase as you go deeper into the subsurface, the changes that take place in rocks become more profound - at sufficiently high temperature and pressure, diagenesis ends and metamorphism begins: a new assemblage of minerals forms, and/or mineral grains become aligned parallel to each other

Which of the following statements is FALSE? Shields Select one: a. make up large areas of Canada, southern Africa, and South America. b. are composed of extensive areas of sedimentary layers laid down on lava flows. c. are composed of rocks that were metamorphosed during ancient mountain-building events. d. are composed of some of the oldest rock on Earth (Precambrian).

- are composed of extensive areas of sedimentary layers laid down on lava flows. - Any sedimentary layers or lava flows that might have been present have eroded away, exposing the deep, ancient metamorphic rock of the shield.

The Middle Paleozoic Era (Silurian-Devonian Periods, 444-359 Ma)

- as the world entered the Silurian Period, global climate warmed, sea level rose, and the continents flooded once again - distinct orogenies took place, yielding new mountain belts during the middle Paleozoic Era - The Caledonian, Acadian, and Antler orogenies all shed deltas of sediment onto the continents; these deposits formed thick successions of red beds - new species of trilobites, gastropods, crinoids, and bivalves replaced species that had disappeared during the mass extinction at the end of the Ordovician Period - on land, vascular plants with woody tissues, seeds, and veins (for transporting water and food) rooted for the first time. - by the Late Devonian Period, the land surface hosted swampy forests with tree-sized relatives of club mosses and ferns - spiders, scorpions, insects, and crustaceans began to exploit both dry-land and freshwater habitats, and jawed fish such as sharks and body fish began to cruise the oceans - at the very end of the Devonian Period, the first amphibians crawled out onto land and inhaled air with lungs

Dynamic Metamorphism

- at depths greater than 15km, rock is so warm that it behaves like soft plastic as shear along the fault takes place, and the minerals in the rock recrystallize - dynamic metamorphism: occurs as a consequence of shearing alone under metamorphic conditions, without requiring a change in temperature or pressure - mylonite (the resulting rock) has a foliation that roughly parallels the fault - mylonites are very fine-grained, due to processes during dynamic metamorphism that replace larger crystals with a mass of very tiny ones - takes place anywhere that faulting occurs at depth in the crust, thus mylonites can be found at all plate boundaries, in rifts, and in collision zones

Classifying clastic sedimentary rocks

- clast size: diameter of fragments or grains making up a rock; clast size in order from coarsest to finest: boulder, pebble, sand, silt, clay - clast composition: may be composed of rock fragments or individual mineral grains - angularity: the degree to which clasts have smooth or angular corners and edges - sphericity: the degree to which the shape of a clast resembles a sphere - sorting: well-sorted sediment consists entirely of sediment of the same size, while poorly sorted sediment contains a mixture of more than one clast size - character of cement: in some clastic sedimentary rocks, the cement consists predominantly of quartz, while in others, it consists predominantly of calcite

The Early Paleozoic Era (Cambrian-Ordovician Periods, 542-444 Ma)

- at the beginning of the Paleozoic Era, Pannotia broke up, yielding smaller continents including Laurentia (composed of North America and Greenland), Gondwana (South America, Africa, Antarctica, India, and Australia), Baltica (Europe), and Siberia - sea level rose, so that vast areas of continental interiors were flooded with shallow seas called epicontinental seas. these regions are now cratonic platforms - in many places, water depths in epicontinental seas reached only a few meters, creating a well-lit marine environment in which life abounded - deposition in these seas yielded layers of fossiliferous sediment - regressions and transgressions of the coast took place, the former marked by unconformities and the latter by accumulations of sediment - the layer cake of strata in the Grand Canyon is rock formed from such sediment - In the Middle Ordovician Period, Laurentia's eastern margin rammed into a volcanic island art and other crustal fragments - the resulting collision, called the Taconic orogeny, deformed and metamorphosed strata of the continent's margin and produced a mountain range in what is now the eastern part of the Appalachians - Cambrian explosion: soon after the Cambrian began, life underwent remarkable diversification - first animals to appear in the Cambrian Period had simple tube or cone shaped shells, and became more complex shortly after - shells may have evolved as a means of protection against predation by organisms such as conodonts, small, eel-like organisms with hard parts that resemble teeth - by the end of the Cambrian tribolites were grazing the sea floor, along with mollusks, brachiopods, nautiloids, gastropods, graptolites, and echinoderms - the Ordovician Period saw the first crinoids and the first vertebrate animals, jawless fish - at the end of the Ordivician, mass extinction took place, perhaps because of the brief glaciation and associated sea-level lowering of the time

Bedding and Stratification

- bed: a single layer of sediment or sedimentary rock with a recognizable top and bottom - bedding plane: boundary between two beds - strata: several beds together - bedding/stratification: the overall arrangement of sediment into a sequence of beds - successive beds have different colors, textures, and resistance to erosion, so bedding gives outcrops a striped appearance - stratigraphic formation: a sequence of strata that is distinctive enough to be traced as a unit across a fairly large region - geologic map: a map that portrays the spatial distribution of rock units at the Earth's surface - William Smith produced the first modern geologic map in 1815

Metamorphism in Subduction Zones

- blueschist is a relatively rare rock that contains an unusual blue-colored amphibole - it requires very high pressure but relatively low temperature to form - blueschist occurs only in the accretionary prisms that form at subduction zones - because prisms grow to be over 20km thick, rock at the base of the prism feels high pressure but the subducted oceanic lithosphere beneath the prism is cool

Physical Weathering

- breaks intact rock into unconnected clasts (grains or chunks), collectively called debris or detritus - jointing: erosion causes rock formerly at depth to rise closer to the Earth's surface, changes in pressure & temperature cause rock to change shape and break; natural cracks that form in rocks due to removal of overburden or due to cooling are known as joints - frost wedging: when water trapped in a joint freezes, it forces the joint open and may cause the joint to grow, helping break blocks free from intact bedrock - salt wedging: dissolved salt in groundwater precipitates and grows as crystals in open pore spaces in rocks; this process pushes apart the surrounding grains and weakens the rock so that when exposes to wind and rain, the rock disintegrates into separate grains - root wedging: as roots grow, they apply pressure to their surroundings and can push joints open - thermal expansion: heat causes the outer layer of a rock to expand, cooling causes this layer to contract; this change creates forces in the rock sufficient to make the outer part of the rock break off in sheet-like pieces - animal attack: burrowing creatures, from earthworms to gophers, push open cracks and move rock fragments

A clastic sedimentary rock composed of angular pebble-sized fragments surrounded by matrix is Select one: a. arkose. b. conglomerate. c. quartzite. d. shale. e. breccia.

- breccia - Conglomerate fragments are rounded, shale is made of clay-size particles, and arkose contains sand-sized particles made of quartz and feldspar.

Geologic Principles for Defining Relative Age

- building from the work of Steno, Hutton, and others, geologist Charles Lyell (1797-1875) laid out a set of formal, usable geologic principles - the principle of original horizontality: states that the layers of sediment, when first deposited, are fairly horizontal, because sediments accumulate on surfaces of low relief in a gravitational field - the principle of superposition: states that in a sequence of sedimentary rock layers, each layer must be younger than the one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect; the layer at the bottom of a sequence is the oldest, and the layer at the top is the youngest - the principle of lateral continuity: states that sediments generally accumulate in continuous sheets within a given region - the principle of cross-cutting relations: states that if one geologic feature(fault, dike) cuts across another, the feature that has been cut is older - the principle of baked contacts: states that an igneous intrusion "bakes" (metamorphoses) surrounding rocks, so the rock that has been baked must be older than the intrusion - the principle of inclusions: states that a rock containing an inclusion (fragment of another rock) must be younger than the inclusion

Recrystallization

- changes the texture (shape and size) of the grains. - the recrystallization process doesn't change the identity or chemical composition of the mineral, it just produces larger crystals of the mineral so it changes the texture of the grains. Plastic deformation occurs when rocks behave like soft plastic; neocrystallization forms new minerals that differ from the protolith; and pressure solution occurs when grains push against each other and cause dissolution.

Chemical Weathering

- chemical reactions alter or destroy minerals when rock comes in contact with water solutions and/or air - dissolution: minerals dissolve into water, primarily affects salts and carbonate minerals, but even quartz dissolves slightly - hydrolysis: water chemically reacts with minerals and breaks them down to form other minerals; hydrolysis reactions in feldspar produce clay - oxidation: transform iron-bearing minerals (such as biotite and pyrite) into a rusty brown mixture of various iron-oxide and iron-hydroxide minerals; iron-bearing rocks can "rust" - hydration: the absorption of water into the crystal structure of minerals, causes some minerals, such as certain types of clay, to expand; such expansion weakens rock - bacteria pluck off molecules from minerals and use the energy from the molecules' chemical bonds to supply their own life force

Which of the following lists accurately describes grain size increasing from smallest to largest? Select one: a. clay, silt, sand b. sand, cobbles, pebbles c. silt, clay, sand d. sand, silt, pebbles

- clay, silt, sand

Soil-forming factors

- climate: large amounts of rainfall and warm temperatures accelerate chemical weathering and cause most of the soluble elements to be leached, while small amounts of rainfall and cooler temperatures result in slower rates of weathering and leaching, so soils take a long time to develop and can retain unweathered minerals and soluble components - substrate composition: different substrates consist of different minerals, so the soils formed on them end up with different chemical compositions; some soils form on basalt, granite, volcanic ash, and recently deposited quartz silt - slope steepness: soil thickness increases as the slope angle decreases - wetness: wet soils tend to contain more organic material than do dry soils - time: young soil tends to be thinner and less developed than an old soil - vegetation type: different kinds of plants extract or add different nutrients and quantities of organic matter to a soil

Which of the following processes CANNOT occur in the formation of metamorphic rock? Select one: a. complete remelting of the rock, followed by solidification to form a new rock b. the segregation of minerals into layers of different compositions c. the realignment of minerals so that they develop a preferred orientation d. the solid-state rearrangement of atoms or ions to create a new assemblage of minerals

- complete remelting of the rock, followed by solidification to form a new rock

Compression, Shear, and Preferred Orientation

- compression: flattens a material - shear: moves one part of a material sideways, relative to another - rocks subjected to compression and shear at elevated temperatures and pressures can change shape without breaking - platy grains become parallel to one another, and elongate grains align in the same direction - inequant grains: platy and elongate grains, dimension on a grain is not the same in all directions - equant grains: have roughly the same dimensions in all directions - preferred orientation: the result of the alignment of inequant minerals in a rock

Organic Sedimentary Rocks

- consists of carbon-rich relicts of plants or other organisms - the organic debris settles along with other sediment and eventually gets buried - when lithified, organic-rich sediment becomes organic sedimentary rock - coal: black, combustible rock consisting of over 50-90% carbon; forms when plant remains have been buried deeply enough and long enough for the material to become compacted and to lose significant amounts of volatiles (hydrogen, water, CO2, ammonia)

Clastic sedimentary rock

- consists of cemented-together clasts, solid fragments and grains broken off of preexisting rocks - comes from the Greek klastos, meaning broken

Sediment

- consists of loose fragments of rock or minerals broken off bedrock, mineral crystals that precipitate directly out of water, and shells or shell fragments -produced by weathering(physical and chemical breakdown) of preexisting rock

Soil

- consists of rock or sediment that has been modified by physical and chemical interaction with organic material, rainwater, and organisms over time - first, chemical and physical weathering produces loose debris, new minerals (such as clay), and ions in solution - second, rainwater carries dissolved ions and clay flakes downward - zone of leaching: region in which downward transport takes place; leaching: extracting, absorbing, and removal - farther down, new mineral crystals precipitate directly out of the water or form by reaction of the water with debris, and the water leaves behind its load of fine clay - zone of accumulation: region in which new minerals and clay collect - third, microbes, fungi, plants, and animals interact with sediment by producing acids that weather grains, by absorbing nutrient atoms, and by leaving behind organic waste and remains - soils typically develop distinct zones, known as soil horizons, arranged in a vertical sequence called a soil profile

The mineral assemblage within metamorphic rock is

- dependent on both the bulk composition of its protolith and the temperature and pressure of formation

Radioactive Decay

- different versions of an element, called isotopes of the element, have the same atomic number but a different atomic weight - radioactive decay: radioactive isotopes are unstable in that eventually, they undergo a change which converts them to a different element - the isotope that undergoes decay is the parent isotope, while the decay product is the daughter isotope - half-life: the measurement of how long it takes for half of a group of parent isotopes to decay

Dynamothermal (Regional) Metamorphism

- due to development of mountain ranges, rock that was once near the Earth's surface along the margin of a continent ends up at great depth beneath the mountain range - the protolith heats up because of the geothermal gradient and because of igneous activity - it endures greater pressure because of the weight of overburden - it undergoes compression and shearing and transforms into foliated metamorphic rock - dynamothermal metamorphism: metamorphism involves not only heat but also compression and shearing - regional metamorphism: such metamorphism affects a large area

Where do you find metamorphic rocks?

- exhumation: the overall process by which deeply buried rocks end up back at the surface - as continents squeeze together during collision, rock is pushed up; the upward movement takes place by slip on faults and by plastic-like flow of rock - rock at depth softens due to heat and the mountain belt collapses under its own weight and becomes thinner - erosion(weathering, landslides, river flow, and glacial flow) grinds away and removes rocks - shield: a broad region of long-lived, stable continental crust where Phanerozoic sedimentary cover either was not deposited or has been eroded away so that Precambrian rocks are exposed - these rocks were metamorphosed during a succession of Precambrian mountain-building events that led to the original growth of continents

Which of the following does NOT describe a change induced on protolith rocks due to mountain building as a result of convergent-margin tectonics and continental collision? Select one: a. Compression and shearing metamorphose the once surface rock. b. Surface rock is sent to great depths beneath the new mountain belt. c. The once surface rock heats up due to igneous activity and the geothermal gradient. d. Hot magma rising beneath the converging continents heats seawater, which then rises through the crust to react with the surface rocks.

- hot magma rising beneath the converging continents heats seawater, which then rises through the crust to react with the surface rocks. - during hydrothermal metamorphism at mid-ocean ridges, hot magma rises beneath the ridge axis, where it heats seawater to create hydrothermal fluids—but this does not happen during mountain building.

Foliated Metamorphic Rocks

- foliation: the parallel surfaces and/or layers that can occur in a metamorphic rock, give a striped or streaked appearance and the ability to split into thin sheets - Slate: finest-grained foliated metamorphic rock, forms by metamorphism of shale or mudstone (rocks composed dominantly of clay) under relatively low pressures and temperatures; contains slaty cleavage, which allows it to split into thin sheets - Phyllite: fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained white mica; the parallelism of translucent fine-grained mica gives phyllite a silky sheen known as phyllitic luster - Metaconglomerate: under the metamorphic conditions that produce slate or phyllite, a protolith of conglomerate becomes metaconglomerate; pressure solution and plastic deformation flatten pebbles and cobbles into pancake-like shapes, and the alignment of inequant clasts defines a foliation - Schist: medium- to coarse-grained metamorphic rick that possesses a type of foliation, called schistosity, defined by the preferred orientation of large mica flakes (muscovite and/or biotite); forms at a higher temperature than does phyllite - Gneiss: a compositionally layered metamorphic rock, typically composed of alternating dark-colored and light-colored layers that range in thickness from millimeters to meters that give gneiss a striped appearance, also known as gneissic banding; can form when the protolith undergoes an extreme amount of shearing under conditions in which the rock can flow like soft plastic, transforming preexisting compositional contrasts in the rock into aligned sheets - Migmatite: under certain condition, gneiss may begin to melt, producing felsic magma and residual, still solid, mafic rock; if the melt freezes again, a mixture of igneous rock and relict metamorphic rock forms (migmatite); migmatite is part metamorphic and part igneous

The Archean Eon: Birth of the Continents and Life

- from 3.85 Ga to 2.5 Ga - 3.85 Ga: the time at which substantial quantities of crustal rocks, including rocks that originated as marine sediments, formed - significant volumes of new continental crust were generated - early crust formed from mafic igneous rocks that originally extruded or intruded at convergent plate boundaries and/or at hot-spot volcanoes - arcs and plateaus collided to form larger blocks that remained at Earth's surface - collisions continued, and the blocks coalesced into still larger proto-continents, which slowly cooled and became stronger - between 3.2 and 2.7 Ga, the first long-lived blocks of durable continental crust came into existence - by the end of the Archean Eon, about 80% of the Earth's continental area had formed - oceans filled in the Archean and have existed ever since - atmosphere changed from being a foggy mixture of water and carbon dioxide into being a transparent gas dominantly composed of nitrogen - oldest undisputed fossil forms of bacteria and archaea occur in 3.2 Ga rocks -stromatolites: distinctive layered mounds of sediment - stromatolites that developed after about 3.2 Ga form because cyanobacteria secrete a mucus-like substance to which sediment settling from water sticks. As the mat gets buries, new cyanobacteria colonize the top of the sediment, building a mound upward - recent researchers suggest that submarine hot-water vents, so-called black smokers, served as the hosts of the first organisms - earliest life in the Archean Eon may have been thermophilic (heat-loving) bacteria or archaea that dined on pyrite at dark depths in the ocean alongside these vents - later in the Archean, organisms evolved the ability to carry out photosynthesis, and moved into shallower, well lit water - By the end of the Archean Eon, plate tectonics had commenced, continental drift was taking place, collisional mountain belts were forming, and erosion was occurring

The Proterozoic Eon: The Earth in Transition

- from about 2.5 Ga to the beginning of the Cambrian Period at 542 Ma - almost half of Earth's history - new continental crust continued to form, but at slower rates, and by the middle of the eon, over 90% of the Earth's continental crust had formed - interior regions of continents slowly cooled and strengthened until they became very rigid and durable - craton: a region of cold, relatively stable continental crust - all cratons that exist today had formed by about 1 Ga; crust in cratons ranges from about 3.85 to about 1 Ga - Successive collisions ultimately brought together most continental crust on Earth into a single supercontinent, name Rodinia, by around 1 Ga - sometime between 800 and 600 Ma, Rodinia "turned inside out", in that Antarctica, India, and Australia broke away from western North America and swung around and collided with the future South America, possibly forming a short-lived supercontinent referred to as Pannotia - when the Proterozoic began, most life was prokaryotic, meaning that it consisted of single-celled organisms(archaea and bactera) without a nucleus - eukaryotic life, consisting of cells that have nuclei, originated as early as 2.7 Ga - the first possible body fossil of a eukaryotic organism occurs in 2.1 Ga - abundant body fossils of eukaryotic organisms can be found only in rocks younger than about 1.2 Ga - ciliate protozoans, single-celled organisms coated with fibers that give them mobility, appear at about 750 Ma - sediments deposited as early as 620 Ma and certainly by 565 Ma contain several types of multicellular organisms that together consistute the Ediacara fauna, named for a region in southern Australia where fossils of these organisms were first found - Ediacaran species survived into the beginning of the Cambrian before becoming extinct - their fossil forms suggest that some of these invertebrate organisms resembled jellyfish, while others resembled worms - it was not until about 2.4 Ga that the concentration of oxygen in the atmosphere increased dramatically - the great oxygenation event happened when other environments were no longer able to absorb or dissolve the oxygen produced by organisms, so the oxygen began to accumulate as a gas in air - oceans became oxidizing environments that could no longer contain large quantities of dissolved iron - between 2.4 Ga and 1.8 Ga, huge amounts of iron settled out of the ocean to form colorful sedimentary beds known as banded iron formation (BIF) - BIF consists of alternating layers of iron oxide minerals (hematite or magnetite) and jasper (red chert) - accumulations of glacial sediments occur worldwide in late Proterozoic stratigraphic sequences - snowball Earth: glaciers covered the land and perhaps the entire ocean surface froze, causing many life forms to die - due to the addition of volcanic CO2 to the atmosphere, Earth warmed up and eventually the glaciers melted

The Hadeon Eon: Before the Rock Record

- from the birth of Earth(4.57Ga) to 3.85 Ga - by 4.5 Ga, the Earth underwent internal differentiation - gravity pulled molten iron down to the center of the Earth, where it accumulated to form the core, leaving a mantle composed of ultramafic rock - formation of the Moon from a ring of silicate-rock debris orbiting the Earth (due to a Mars-sized protoplanet colliding with the Earth) - Earth was so hot that much of its surface was an ocean of magma - at about 4.4 Ga, the amount of radioactive heat generation decreased, so solid rocks might have formed (geologists have found 4.4 Ga grains of a durable mineral called zircon) - outgassing of the Earth's mantle - volatile (gassy) elements or compounds originally incorporated in mantle minerals were released and bubbled out of volcanoes, along with lava - between 4.0 and 3.85 Ga, all inner planets of the Solar System underwent intense meteor bombardment, and only after it ceased could long-lasting crust, atmosphere, and oceans begin to form - murky, dense carbon dioxide and sulfur dioxide rich air

The Geologic Column

- geologic column: by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column that represents the entirety of Earth history - largest subdivisions break Earth history into the Hadean, Archean, Proterozoic, and Phanerozoic Eons (the first three together constitute the Precambrian) - the Phanerozoic Eon is subdivided into eras: from oldest to youngest, they are the Paleozoic (ancient life), Mesozoic (middle life), and Cenozoic (recent life) Eras - eras are divided into periods and each period into epoch - Cambrian explosion: the appearance of invertebrates with shells defines the Precambrian-Cambrian boundary; at this time, there was a sudden diversification of life, with many new types of organisms appearing over a relatively short interval

Dating Sedimentary Rocks

- geologists obtain dates for sedimentary rocks by studying cross-cutting relationships between sedimentary rocks and datable igneous or metamorphic rocks

Dormant Volcano

- have not erupted in 100's to 1000's years, but may erupt again in the future - Mt. Kilimanjaro is dormant

Metamorphism due to heating

- heat causes the atoms in a mineral grain to vibrate rapidly and stretch and bend their chemical bonds - if bonds stretch too far and break, atoms detach from their original neighbors, move slightly, and form new bonds with other atoms - solid-state diffusion: rearrangement of atoms within grains, or migration of atoms into and out of grains - recrystallization and/or neocrystallization take place - most metamorphic rocks form at temperatures between 250C and 850C

Which of the following rocks is classified as nonfoliated? Select one: a. slate b. phyllite c. schist d. hornfels

- hornfels - Hornfels is a nonfoliated metamorphic rock because it was formed in the absence of differential stress.

Hydrothermal Metamorphism at Mid-Ocean Ridges

- hot magma rises beneath the axis of mid-ocean ridges, so when cold seawater sinks through cracks down into the oceanic crust along ridges, it heats up and transforms into hydrothermal fluid - this fluid then rises through the crust, near the ridge, causing hydrothermal metamorphism of ocean-floor basalt - fluid escapes through vents back into the sea, called black smokers

Metamorphic aureoles typically contain nonfoliated rock like hornfels because

- they form adjacent to an intruding pluton, which provides heat for metamorphism. - Aureoles typically form around igneous intrusions by contact/thermal metamorphism. The addition of heat, but little pressure, produces nonfoliated metamorphic rocks.

Isotopic Dating

- in the 1950s, geologists developed techniques for using measurements of radioactive elements to calculate the numerical ages of rocks - carbon dating is not used for dating rocks because appropriate carbon isotopes occur only in organisms and radioactive carbon has a very short half-life - collecting the rocks(unweathered rocks), separating the minerals, extracting parent and daughter isotopes(dissolving minerals in acid or evaporating portions of them with a laser), and analyzing the parent-daughter ratio(mass spectrometer: an instrument that uses a strong magnet to separate isotopes from one another according to their respective weights and can count the number of atoms of specific isotopes separately) - closure temperature: the temperature below which isotopes are no longer free to move - if we date minerals in a sedimentary rock, we determine only when these minerals first crystallized as part of an igneous of metamorphic rock, not the time when the minerals were deposited as sediment nor the time when the sediment lithified to form a sedimentary rock - isotopic dating can only be applied to igneous and metamorphic rocks

Which of the following statements is FALSE? Mylonite Select one: a. is a product of gneiss melting to produce felsic magma and solid mafic rock. b. is produced by shear stress on softened rock. c. forms by recrystallization in a fault zone. d. has pronounced foliation parallel to the direction of faulting.

- is a product of gneiss melting to produce felsic magma and solid mafic rock. - A migmatite (not mylonite) is a product of gneiss melting to produce a felsic magma and a still-solid mafic rock.

Tension (a type of stress) :

- is created by a pull perpendicular to a surface. - tension is a stress created by pulling perpendicular to a surface, such as grabbing two ends of a piece of taffy and pulling your hands apart. A balloon collapses in a pool because of pressure; shear occurs when rocks move sideways; and pressure (again) occurs when compression is exerted equally from all sides.

What is the protolith of marble?

- limestone - a protolith is the parent rock that is metamorphosed into a different rock; metamorphosed limestone is marble.

Lithification of Clastic Sedimentary Rocks

- lithification of an accumulation of angular clasts yields breccia - layers of river gravel lithify into conglomerate - layers of beach or dune sand lithify into sandstone - layers of mud, exposed beneath marsh grass, lithify to form shale

Biochemical Sedimentary Rocks: Chert(biochemical)

- made from cryptocrystalline quartz (crypto="hidden" in Greek), meaning quartz grains that are too small to be seen without extreme magnification of an electron microscope - if hit with a hammer, the rock would crack to form smooth, spoon-shaped (conchoidal) fractures -the chert beneath the Golden Gate Bridge formed from shells of silica-secreting plankton that accumulated on the sea floor - after burial, the shells gradually dissolved, forming a silica-rich gel - chert then formed when this gel solidified

Chemical Sedimentary Rocks

- made up of minerals that precipitated directly from water solutions Evaporites - salt precipitation occurs where saltwater becomes supersaturated, meaning that it has exceeded its capacity to contain more dissolved ions - ions bond to form solid grains that either settle out of the water or grow on the floor of the water body - supersaturated saltwater develops where evaporation removes water from a water body faster than the rate at which new water enters - takes places in desert lakes and along the margins of restricted seas - because salt deposits form as a consequence of evaporation, geologists refer to them as evaporites - when 80% of the water evaporates, gypsum forms, and when 90% evaporates, halite precipitates Travertine (chemical limestone) - rock composed of crystalline calcium carbonate formed by chemical precipitation from groundwater than has seeped out at the ground surface either in hot or cold water springs, or on the walls of caves - precipitation can happen when the groundwater degasses, when water evaporates, and due to biologic activity of various kinds of microbes Dolostone - contains the mineral dolomite, which contains equal amounts of calcium and magnesium - forms by a chemical reaction between solid calcite and magnesium-bearing groundwater - a lot of dolostone originated as limestone but later changed into dolostone as dolomite crystals replaced calcite Chert(replacement) - formed when cryptocrystalline quartz gradually replaced calcite crystals within a body of limestone long after the limestone was deposited; geologists call such a material "replacement chert" - comes in many colors: black, white, red, brown, green, gray - petrified wood: chert that forms when silica-rich sediment, such as ash from a volcanic eruption, buries a forest - the silica dissolves in groundwater, and then later precipitates as cryptocrystalline quartz within wood, gradually replacing the wood's cellulose - agate: chert that precipitates in concentric rings and hollows in a rock and ends up with a striped appearance, caused by variations in the content of impurities incorporated in the chert

Which of the following is NOT a common metamorphic facies? Select one: a. mafic b. amphibolite c. greenschist d. blueschist e. granulite

- mafic - the term mafic refers to minerals and/or rocks that are high in iron and magnesium; it does not refer to a metamorphic facies

Choose the listing that shows the rocks in increasing degrees of metamorphism (i.e., from lower to higher grade).

- metaconglomerate, gneiss, migmatite - metaconglomerate is barely metamorphosed; higher heat changes the rock into a gneiss; and migmatite has been so strongly heated, some rock has melted and become new igneous rock.

Thermal or Contact Metamorphism

- metamorphic aureole or contact aureole: the distinct belt of metamorphic rock that forms around an igneous intrusion; the width of an aureole depends on the size and shape of the intrusion, and on the amount of hydrothermal circulation - larger intrusions produce wider aureoles - thermal metamorphism: local metamorphism caused by igneous intrusion that develops in response to heat without a change in pressure and without differential stress - contact metamorphism: local metamorphism caused by igneous intrusion that develops adjacent to the contact of an intrusion with its wall rock - this metamorphism takes place without application of compression or shear, so aureoles contain hornfels, a nonfoliated metamorphic rock

How old is the Earth?

- the oldest rocks are 4.03 Ga, while the oldest meteorites are 4.57 Ga - we don't find rocks older than 4.03 Ga because the Earth might have been so hot that rocks in the crust remained above the closure temperature for minerals, and isotopic clocks could not start "ticking" - another theory is that the inner planets were bombarded so intensely by meteorites at about 4.0 Ga that almost all crust formed earlier than that was completely destroyed - human history occupies the last 0.000001% of Earth history

Soil Erosion

- the removal of soil by running water or by wind - human activities can increase rates of soil erosion by 10 to 100 times

Geologic Time

- the span of time since Earth's formation

Metamorphic Intensity

- metamorphic grade: the amount or degree of metamorphic change - temperature plays the dominant role in determining the extent of recrystallization and neocrystallization during metamorphism - metamorphic rocks that form at relatively low temperatures (250C-400C) are low grade rocks, and those that form at relatively high temperatures (over 600C) are high-grade rocks - intermediate-grade rocks form at temperatures between these two extremes -as grade increases, coarser grains and new mineral assemblages that are stable at higher temperatures and pressures are produced - index minerals: the presence of certain minerals in a rock indicates the approximate metamorphic grade of the rock - isograd: the line on a map along which an intex mineral first appears; all points along an isograd have approximately the same metamorphic grade - metamorphic zones: regions between two isograds; zones are named after an index mineral that was not present in the previous, lower-grade zone

Foliation is the alignment of ________ in a metamorphic rock.

- minerals

Bed-Surface Markings

- mud cracks: if a mud layer dries up after deposition, it cracks into roughly hexagonal plates that typically curl up at their edges; the openings between the plates are mud cracks - scour marks: as currents flow over a sediment surface, they may erode small troughs, called scour marks, parallel to the current flow - fossils: some fossils are shell imprints or footprints on a bedding surface

Metamorphism due to pressure

- near the Earth's surface, minerals with relatively open crystal structures can be stable - if subjected to extreme pressure, the atoms pack more closely together and denser minerals tend to form - phase changes and/or neocrystallization take place - when pressure and temperature both increase, the original mineral assemblage in a rock becomes unstable, and a new assemblage forms out of minerals that are stable

Uniformitarianism

- principle developed by James Hutton(1726-97) - physical processes that operate in the modern world also operated in the past, at roughly the same rates, and these processes were responsible for forming geologic features preserved in outcrops - the present is the key to the past

Relative versus Numerical Age

- relative age: the age of one feature with respect to another in a sequence - numerical age(absolute age): the age of a feature given in years

Ripple Marks, Dunes, and Cross Bedding

- ripple marks: relatively small(generally no more than a few cm high), elongated ridges that form on a bed surface at right angles to the direction of current flow - dunes: relatively large, elongate ridges built of sediment transported by a current; "mega-ripples"; dunes on the bed of a stream: 10's of cm high, wind-formed dunes of deserts: 10's to over 100 meters high - cross beds: distinct internal laminations that are inclined at an angle - cross-bed orientation indicates wind direction at the time of deposition - the boundary between two successive cross-bedded layers is called the "main bedding", and the internal curving surfaces within the layer constitute the cross bedding

Sedimentary rock

- rock that forms at or near the surface of the Earth in one of several ways: by the cementing together of loose clasts (fragments or grains) produced by physical or chemical weathering of preexisting rock; by the growth of shell masses or the cementing together of shells and shell fragments; by the accumulation and subsequent alteration of organic matter from dead plankton or plants; or by the precipitation of minerals from water solutions

If you find quartz sandstone in the place where it formed, you know you are looking at an ancient Select one: a. swamp. b. sand dune. c. alluvial fan. d. marsh. e. avalanche on a submarine slope.

- sand dune - Of the choices, only a sand dune (either in a desert or at a coastline) would consist of quartz sand grains with little to no mud and would result in the formation of a quartz sandstone.

Geologic History

- the succession of events in order of relative age that have produced the rock, structure, and landscape of a region

Formation of Clastic Sedimentary Rocks

- sandstone: consists of loose clasts, known as detritus, that have been stuck together to form a solid mass; feels gritty, small grains of quartz would break free - 1st: weathering: detritus forms by disintegration of bedrock into separate grains due to physical and chemical weathering - 2nd: erosion: combination of processes that separate rock or regolith (surface debris) from its substrate; involves abrasion, falling, plucking, scouring, and dissolution, and is caused by moving air, water, or ice - 3rd: transportation: gravity, wind, or ice carry sediment; ability of a medium to carry sediment depends on its viscosity and velocity - 4th: deposition: process by which sediment settles out of the transporting medium; sediment settles out of wind or moving water when these fluids slow, because as the velocity decreases, the fluid no longer has the ability to carry sediment; sediment is deposited by ice when the ice melts - 5th: lithification: transformation of loose sediment into solid rock; compaction: once the sediment has been buried, pressure caused by the weight of overlying material squeezes out water and air that had been trapped between clasts, and clasts press together tightly; cementation: compacted sediment may then be stuck together to make coherent sedimentary rock

Types of Volcanoes

- shield volcanoes, cinder cones, strato (composite) volcanoes, lava domes, caldera & ash sheets

Sedimentary rocks can form by each of the following processes EXCEPT Select one: a. by the cementing together of loose grains of pre-existing rock. b. solidification from a melt. c. from shell fragments or carbon-rich relicts of plants. d. by the precipitation of minerals from water solution.

- solidification from a melt - rocks that solidify from a melt are igneous

The Phanerozoic Eron

- starts in 542 Ma - the Phanerozoic Eon consists of three eras: - the Paleozoic (Greek for ancient life) - the Mesozoic (middle life) - the Cenozoic (recent life) - geologists have divided the Mesozoic and Cenozoic each into 3 periods and the Paleozoic into 6 periods

Stratigraphic Formations

- stratigraphic formations: a sequence of beds of a specific rock type or group of rock types that can be traced over a fairly broad region - the boundary surface between two formations is a type of geologic contact - commonly, geologists name a formation after a locality where it was first identified or first studied - if a formation consists of only one rock type, we may incorporate that rock type in the name - several adjacent formations in a succession may be lumped together as a stratigraphic group - correlation: defined by Smith, the stratigraphic relationship between the strata at one locality and the strata at another - lithologic correlation: geologists correlate formations between nearby regions based on similarities in rock type - marker bed: a particularly unique layer that provides a definitive basis for correlation - fossil correlation: to correlate rock units over broad areas, we must rely on fossils to define the relative ages of sedimentary units

Sedimentary Basins

- subsidence: thick accumulations of sediments form only in special regions where the surface of the Earth's lithosphere sinks, providing space in which sediment collects - sedimentary basin: sediment-filled depression - Rift basins: form in continental rifts, regions where the lithosphere is stretching horizontally, and therefore thins vertically; as the rift grows, slip on faults drops blocks of crust down, producing low areas bordered by narrow mountain ridges, which fill with sediment - Passive-margin basins: form along the edges of continents that are not plate boundaries, form because subsidence of stretched lithosphere continues long after rifting ceases; they fill with sediment carried to the sea by rivers and with carbonate rocks formed in coastal reefs - Intracontinental basins: develop in the interiors of continence, initially because of subsidence over a rift, may continue to subside in pulses even hundreds of millions of years after forming - Foreland basins: form on the continent side of a mountain belt because the forces produced during convergence or collision push large slices of rock up faults and onto the surface of the continent; the weight of these slices pushes down on surface of the lithosphere, producing a wedge-shaped depression adjacent to the mountain range that fills with sediment eroded from the range; fluvial and deltaic strata accumulate here

The Late Paleozoic Era (Carboniferous-Permian Periods, 359-251 Ma)

- the climate cooled significantly in the late Paleozoic - seas gradually retreated from continents, so that during the Carboniferous Period, regions that had hosted the limestone-forming reefs of epicontinental seas now became coastal areas and river deltas in which sand, shale, and organic debris accumulated - Laurentia lay near the equator, so it had tropical and semi-tropical conditions that favored lush growth in swamps - this growth left thick piles of plant debris that transformed into coal after burial - much of Gondwana and Siberia lay at high latitudes and became covered by ice sheets by the Permian Period - a succession of continental collisions, culminating in the formation of a single super continents, Pangaea - the largest collision occurred during Carboniferous and Permian time, when Gondwana rammed into Laurentia and Baltica, causing the Alleghanian orogeny of North America - during this event, the final stage in the development of the Appalachians, eastern North America rammed against northwestern Africa, and what is now the Gulf Coast region of North America squashed against the northern margin of South America - a vast mountain belt grew, in which deformation generated huge faults and folds - along the continental side of the range, a wide band of deformation called the Appalachian fold-thrust belt formed - Ancestral Rockies: movements of faults produced uplifts and sediment-filled basins in the Midwest and in the region of the present-day Rocky Mountains. - in coal swamps, fixed-wing insects including huge dragonflies flew through a tangle of ferns, club mosses, and scouring rushes, and by the end of the Carboniferous Period insects such as the cockroach, with foldable wings, appeared - In the Permian Period, forests containing gymnosperms ("naked seed" plants such as conifers) and cycads (trees with a palm-like stalk and fern-like fronds) became widespread - amphibians and ,later, reptiles populated the land - the appearance of reptiles marked the evolution of a radically new component in animal reproduction: eggs with a protective covering - such eggs permitted reptiles to reproduce without returning to the water - the late Paleozoic Era came to a close with a major mass-extinction event, during which over 95% of marine species disappeared - according to one hypothesis, the terminal Permian mass extinction occurred as a result of an episode of extraordinary volcanic activity in the region that is now Siberia; basalt sheets extruded during the event are known as the "Siberian traps" - eruptions could have clouded the atmosphere, acidified the oceans, and disrupted the food chain

Nonfoliated Metamorphic Rocks

- the lack of foliation means either that metamorphism occurred in the absence of compression and shear, or that most of the new crystals can only grow in an equant form - Hornfels: fine-grained nonfoliated rock that contains a variety of metamorphic minerals - Quartzite: forms by the metamorphism of pure quartz sandstone; when quartzite cracks, the fracture cuts across grain boundaries, while fractures in sandstone curve around grains; looks glassier than sandstone and does not have its grainy, sandpaper-like surface; can vary in color from white to gray, purple, or green - Marble: the metamorphism of limestone yields marble, consisting of a fairly uniform mass of interlocking calcite crystals; variety of colors: white, pink, green, and black - not all marble in nonfoliated: if original protolith contained layers with different impurities, and shear caused the marble to flow plastically, the resulting marble has color banding

Transgression and Regression

- transgression: when relative sea level rises, the shoreline migrates inland - regression: when relative sea level falls, the coast migrates seaward - the process of transgression and regression leads to the formation of broad blankets of sediment

Toba super-eruption 73,000 years ago

- triggered global cooling for 10-1000 years - may have led to extinctions - may have killed all but 3,000-10,000 humans on Earth - All humans descended from single ancestor dating to this time?

Turbidity Currents and Graded Beds

- turbidity current: an earthquake or storm triggers an underwater avalanche - in a turbidity current, sediment and water flow chaotically downslope - as the turbidity current slows, larger grains settle first, followed by progressively finer grains - as the process repeats, a succession of graded beds accumulates - graded bed: a layer of sediment in which grain size varies from coarse at the bottom to fine at the top - geologists refer to a deposit from a turbidity current as a turbidite

Unconformities

- unconformity: a surface representing a period of nondeposition and possibly erosion - hiatus: the gap in the geologic record than an unconformity represents - angular unconformity: rocks below an angular unconformity were tilted or folded before the unconformity developed; an angular unconformity cuts across the underlying layers, and the orientation of layers below and unconformity differs from the layers above - nonconformity: sedimentary rocks overlie generally much older intrusive igneous rocks and/or metamorphic rocks; the igneous or metamorphic rocks underwent cooling, uplift, and erosion prior to becoming the substrate, or basement, on which new sediments accumulated - disconformity: layers of sediment accumulate, sea level drops and an erosion surface forms, sea level rises and new sedimentary layers accumulate; the boundary between the two sequences is a disconformity

Hydrothermal fluids

- very hot-water solutions - these fluids chemically react with rock and accelerate metamorphic reactions, because atoms involved in the reactions can migrate faster through a fluid than they can through a solid, and hydrothermal fluids provide water that can be absorbed by minerals during metamorphic reactions - metasomatism: fluids passing through a rock may pick up some dissolved ions and drop off others, thus changing the overall chemical composition of a rock during metamorphism

The breakdown of exposed rock into small fragments and dissolved ions is termed

- weathering

Shock Metamorphism

- when large meteorites slam into the Earth, a vast amount of kinetic energy instantly transforms into heat, and a pulse of extreme compression (a shock wave) propagates into the Earth - this heat may be sufficient to melt or even vaporize rock at the impact site, and the extreme compression of the shock wave causes quartz in rocks below the impact site to undergo a phase change and become a more compact mineral called coesite - shock metamorphism: the changes in rock due to the passage of a shock wave

Hazards associated with volcanoes

-Pyroclastic flows (Nuée ardentes) -Tsunami -Lahars -Ash falls -Gases -Lateral blasts (landslides) -Lava flows

Burial Metamorphism

-at depths greater than about 8 to 15 km, depending on the geothermal gradient, temperatures may be great enough for metamorphic reactions to begin, and low-grade metamorphic rock form - burial metamorphism: metamorphism due only to the consequences of very deep burial

Active Volcano

-erupting, erupted recently, or likely to erupt soon -Mount Saint Helens, last erupted July 10,2008, is an active volcano

Extinct Volcanoes

-were active in geological past (>10,000 yrs ago), but will not erupt again

InSAR

Interferometric synthetic aperture radar

The application of ________ during metamorphism causes elongated crystals to align parallel with each other. When this happens, the rock develops ________.

differential stress; foliation

Can volcanic eruptions be predicted?

sometimes