Ch 10, 11, 2

radiometric dating

(also called numerical dating) The science of determining the age of materials in years by measuring the ratio of parent radioactive atoms to daughter product atoms in the material.

numerical age

(in older literature, "absolute age") The age of a geologic feature given in years.

fracture zone

A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault.

apparent polar-wander path

A path on the globe along which a magnetic pole appears to have wandered over time; in fact, the continents drift, while the magnetic pole stays fairly-fixed.

triple junction

A point where three lithosphere plate boundaries intersect.

Uniformitarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes

differentiation

A process early in a planet's history during which dense iron alloy melted and sank downward to form the core, leaving less- dense mantle behind.

ridge-push force

A process in which gravity causes the elevated lithosphere at a mid-ocean ridge axis to push on the lithosphere that lies farther from the axis, making it move away.

parent atom

A radioactive isotope that undergoes decay.

stratigraphic formation

A recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region.

angular unconformity

An unconformity in which the strata below were tilted or folded before the unconformity developed; strata below the unconformity therefore have a different tilt than strata above.

What do geologists date to determine when the Earth formed?

Geologists commonly use radiometric dating methods, based on the natural radioactive decay of certain elements such as potassium and carbon, as reliable clocks to date ancient events.

When in Earth history did vascular plants appear? When did trees appear?

Middle Paleozoic, Late Paleozoic

closure temperature

The temperature at which ions can no longer move in or out of a mineral quickly; when a rock drops below the closure temperature for a mineral, the mineral can be used for isotopic dating.

theory of plate tectonics

The theory that the outer layer of the Earth (the lithosphere) consists of separate plates that move with respect to one another.

Great oxygenation event

The time in Earth's history, about 2.4 Ga, when the concentration of oxygen in the atmosphere increased dramatically.

polarity subchron

The time interval between magnetic reversals if the interval is of short duration (less than 200,000 years long).

chron

The time interval between successive magnetic reversals.

half-life

The time it takes for half of a group of a radioactive element's isotopes to decay.

Identify the major geologic features of a convergent boundary in the figure shown.

When the crust breaks open because of the plates spreading apart, hot magma bubbles to the surface. the magma is converted into rock.

What is a stratigraphic formation? Describe two different methods of correlating formations. How was correlation used to develop the geologic column?

Lithologic correlation is where geologists correlate formations between nearby regions based on similarities in rock type.Correlating helped form geologic column by allowing geologists to compare rocks at millions of different places, which helped create the composite stratigraphic columnStratigraphic formation is a sequence of bed of a specific rock type that can be traced over a broad region

geologic map

A map showing the distribution of rock units and structures across a region.

snowball earth

A model proposing that, at times during Earth history, glaciers covered all land, and the entire ocean surface froze.

The North Atlantic Ocean is 3,600 km wide. Seafloor spreading along the Mid-Atlantic Ridge occurs at 2 cm per year. When did rifting start to open the Atlantic?

180 000 000 yrs ago

What is the age of the oldest rocks on the Earth? What is the current estimate of the numerical age of the Earth? Why is there a difference

4.03 Ga, 4.57 Ga. They come off of different planets, so they can e older than Earth rocks

mid-ocean ridge

A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary.

transform boundary

A boundary at which one lithosphere plate slips laterally past another.

divergent boundary

A boundary at which two lithosphere plates move apart from each other; they are marked by mid-ocean ridges.

convergent boundary

A boundary at which two plates move toward each other so that one plate sinks (subducts) beneath the other; only oceanic lithosphere can subduct.

unconformity

A boundary between two different rock sequences representing an interval of time during which new strata were not deposited and/or were eroded.

Basin and Range province

A broad, Cenozoic continental rift that has affected a portion of the western United States in Nevada, Utah, and Arizona; in this province, tilted fault blocks form ranges, and alluvium-filled valleys are basins.

mantle plume

A column of very hot rock that rises up through the mantle.

geologic column

A composite stratigraphic chart that represents the entirety of the Earth's history.

Laurentia

A continent in the early Paleozoic Era composed of today's North America and Greenland.

passive continental margin

A continental margin that does not coincide with a plate boundary, and therefore does not display seismicity.

active margin

A continental margin that is also a plate boundary.

stratigraphic column

A cross-section diagram of a sequence of strata summarizing information about the sequence.

volcanic arc

A curving chain of active volcanoes formed adjacent to a convergent plate boundary.

trench

A deep, elongate trough bordering a volcanic arc; a trench defines the trace of a convergent plate boundary.

index fossil

A fossil of an organism that lived during a relatively short period of time over a relatively large area of the Earth, and can be used for stratigraphic correlation.

fossil assemblage

A group of fossil species found in a specific sequence of sedimentary rock.

How is a hot-spot track produced, and how can hot-spot tracks be used to track the past motions of a plate? Which direction is the plate shown in the figure moving?

A hot spot is a desolate volcano that erupts again when the plate produces movement. The hot spot is usually places far away from the fault line. We can see where a plate might have traveled because of the placement of various hot spots around the ocean.

superplume

A huge mantle plume.

continental rift

A linear belt along which continental lithosphere stretches and pulls apart.

hot spot

A location at the base of the lithosphere, at the top of a mantle plume, where temperatures can cause melting.

craton

A long-lived block of durable continental crust commonly found in the stable interior of a continent.

geologic time scale

A scale that describes the intervals of geologic time.

Wadati-Benioff zone

A sloping band of seismicity defined by intermediate- and deep- focus earthquakes that occur in the downgoing slab of a convergent plate boundary.

Pangaea

A supercontinent that assembled at the end of the Paleozoic Era.

Gondwana

A supercontinent that consisted of today's South America, Africa, Antarctica, India, and Australia. (Also called Gondwanaland.)

Anthropocene

A term used informally in reference to the past few thousand years, to emphasize that during this time, human society has modified the Earth System significantly.

nonconformity

A type of unconformity at which sedimentary rocks overlie basement (older intrusive igneous rocks and/or metamorphic rocks).

accretionary prism

A wedge-shaped mass of sediment and rock scraped off the top of a downgoing plate and accreted onto the overriding plate at a convergent plate margin.

period

An interval of geologic time representing a subdivision of a geologic era.

epoch

An interval of geologic time representing the largest subdivision of a period.

era

An interval of geologic time representing the largest subdivision of the Phanerozoic Eon.

seamount

An isolated submarine mountain.

disconformity

An unconformity parallel to the two sedimentary sequences it separates.

isotopic dating

Another term for radiometric dating, meaning the determination of the numerical age of rocks and minerals.

Why are there no whole rocks on the Earth that yield isotopic dates older than about 4 billion years?

Based on the cratering on the moon, the moon -- as well as all of the inner planets of the Solar System -- underwent intense meteor bombardment between 4.0 and 3.85 Ga. This bombardment pulverized and/or melted most of the Earth's crust at this time.

How does oceanic lithosphere differ from continental lithosphere in thickness, composition, and density?

CONTINENTAL OCEANIC thick (150 kilometers) thinner (70 kilometers)very dense rock non dense rockmafic rock metamorphic rock

Describe the process of continental collision and give examples of where this process has occurred.

Continental Collision- occurs when there is an island near a convergent boundary. The boundary can shift and the island will be pulled under (sub ducted). The ground can either be sub ducted or wrinkle to form mountains or hills. Examples of continental collision on Earth are the Himalayan Mountains and the alps. The Appalachian Mountain range.

Describe the characteristics of a continental rift and give examples of where this process is occurring today.

Continental lithosphere spreads apart and the brittle crust breaks to make rifts. The break could be so large that it separates the mass of land it is underneath, making the mass into two separate pieces.Examples: East African RiftBasin and Range province on Western U.S.

isotopes

Different versions of a given element that have the same atomic number but different atomic weights.

Describe the three types of plate boundaries. Which type of plate boundary does the line labeled with yellow arrows show in the figure?

Divergent- two plates move away from each other Convergent- two plates move toward each other and one plate is pulled under the other. Transform- two plates that slide sideways against each other yellow arrows show an active transform fault

Why did the Himalayas and the Alps form?

From the collision of Africa, India, and Australia plates into Europe/Asia

Mesozoic

K-PG boundary event, faunal turnover

Paleozoic Era

Laurentia, Gondwana, Cambrian explosion, Pangaea

stromatolite

Layered mounds of sediment formed by cyanobacteria; cyanobacteria secrete a mucous-like substance to which sediment sticks, and as each layer of cyanobacteria gets buried by sediment, it colonizes the surface of the new sediment, building a mound upward.

Why is the oldest oceanic lithosphere less than 200 Ma?

It subducts under the continental crust after that

Proterozoic Eon

Most recent of the Precambrian Eons. Rodinia and Pannotia supercontinents. Great oxygenation event.

What continents formed as a result of the breakup of Pangaea? Which ocean is growing on this paleogeographic map?

N, America, Asia, Africa

What major tectonic provinces formed in the western United States during the Cenozoic?

Nevada, Utah, Arizona

Contrast numerical age with relative age.

Numerical Age: the age of a feature given in years Relative Age: the age of one feature with respect to another.

plate

One of about 20 distinct pieces of the relatively rigid lithosphere.

Discuss the major forces that move lithosphere plates.

Plate Tectonics- are responsible for moving the plates. Convection- the magma rises from a crack in the crust and the magma cools and goes through the process of becoming rock and while the rock moves farther away as a result of more magma/rock formation, the older rock is eventually pulled back under the crust. Ridge Push Force- the weight of new rock is pulled down by the force of gravity, causing the two plates to move away from each other. Slab pull force- instead of breaking or wrinkling, plate slides right under the other plate

normal polarity

Polarity in which the paleomagnetic dipole has the same orientation as it does today.

reversed polarity

Polarity in which the paleomagnetic dipole points north.

How did the Alleghanian and Ancestral Rockies orogenies affect North America?

Pre-existing faults in the continental crust clear across N. America became active again, reactivated faulting that produced uplifts

How do geologists obtain an isotopic date? What does the age of an igneous rock mean? What does the age of a metamorphic rock mean?

Radioactive elements decay at a constant rate over time, and they can be measured by comparing the parent isotope with the daughter isotope

How do apparent polar-wander paths show that the continents have moved?

Scientists found rocks of different ages on different continents, where the pole was said to have been, that when studied properly, can tell about the magnetic field at the time of its formation.

Describe the hypothesis of seafloor spreading.

Sea floor spreading is when there is a break in the oceanic crust, called a ridge, caused by the plates moving apart. the break fills in with magma because the oceanic crust is not very thick and it is right above the magma filled mantle. The magma turns into new crust and when the floor breaks apart again, the hardening magma/rock pushes the floor right around it outward, thus causing the widening of the ocean floor.

stratigraphic group

Several adjacent stratigraphic formations in a succession.

rifting

The process by which continental lithosphere stretches horizontally and thins vertically.

subduction

The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate.

correlation

The process of defining the age relations between the strata at one locality and the strata at another.

Describe the plate-tectonic conditions that led to the formation of the Sierran arc and the Sevier fold-thrust belt. What mountain belt in the United States formed during the Laramide Orogeny?

The Sierran arc was a volcanic arc formed by subduction. The Sevier fold-thrust belt was a side effect of the Sierran arc. The Rocky Mountains formed furing the Laramide Orogeny.

relative age

The age of one geologic feature with respect to another.

magnetic inclination

The angle between a magnetic needle free to pivot on a horizontal axis and a horizontal plane parallel to the Earth's surface.

magnetic declination

The angle between the direction a compass needle points at a given location and the direction of true north.

How did the atmosphere change during the first 2 billion years of Earth history? When did most continental crust form?

The atmosphere slowly became more oxygen-rich as solar radiation split water molecules and cyanobacteria began the process of photosynthesis. Eventually the atmosphere became like it is today and rich in oxygen. The first complex organisms on Earth first developed about 2 billion years ago.

Describe the formation of the crust, atmosphere, and oceans during the Hadean Eon.

The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form.

plate boundary

The border between two adjacent lithosphere plates.

black smoker

The cloud of suspended minerals formed where hot water spews out of a vent along a mid-ocean ridge; the dissolved sulfide components of the hot water instantly precipitate when the water mixes with seawater and cools.

suture

The contact defining the boundary of what were two separate crustal blocks, prior to collision.

daughter atom

The decay product of radioactive decay. disconformity

magnetic anomaly

The difference between the expected strength of the Earth's magnetic field at a certain location and the actual measured strength of the field at that location.

How did drilling into the seafloor contribute further proof of seafloor spreading? How did the seafloor-spreading hypothesis explain variations in ocean floor heat flow?

The drilling study was able to date the oceanic material and found that not only were parts of the floor not all the same age but that the new material came from a center source and all the surrounding floor was successively getting older.The breaks would release hot magma that would eventually cool but would remain a warm temperature because the lithosphere is very thin there so the hot magma underneath is radiating heat.

slab-pull force

The force that downgoing plates (or slabs) apply to oceanic lithosphere at a convergent margin.

Describe the principles that allow us to determine the relative ages of geologic events

The geologic history of a region can be determined by using principles such as uniformitarianism, superposition, original horizontality, original continuity, cross-cutting relations, inclusions, and baked contacts.

seafloor spreading

The gradual widening of an ocean basin as new oceanic crust forms at a mid-ocean ridge axis and then moves away from the axis.

magnetic-reversal chronology

The history of magnetic reversals through geologic time.

continental drift

The hypothesis that continents have moved and are still moving slowly across the Earth's surface.

Pleistocene Ice Age

The ice age that began about 2.6 Ma, and involves many advances and retreats of continental glaciers.

Precambrian

The interval of geologic time between the Earth's formation about 4.57 Ga and the beginning of the Phanerozoic Eon 542 Ma.

Alpine-Himalayan chain

The largest orogenic belt on the Earth today, formed by collisions of the former Gondwana continents with the southern margins of Europe and Asia.

eon

The largest subdivision of geologic time.

asthenosphere

The layer of the mantle that lies between 100-150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force.

What are the characteristics of a lithosphere plate? Can a single plate include both continental and oceanic lithosphere?

The lithospheric plate is easily cracked and broken. crust plus the top(cooler) part of the upper mantle, does not flow -yes. It can have oceanic and continental on the same plate.

Archean Eon

The middle Precambrian eon (4.0-2.5 Ga). Birth of the continents.

Why can't we date sedimentary rocks directly? How do we assign numerical ages to intervals on the geologic column to produce a geologic time scale?

The mineral component of sedimentary rocks are generally older than the rock itself

Proerozoic Eon

The most recent of the Precambrian eons (2,500-541 Ma).

absolute plate velocity

The movement of a plate relative to a fixed point in the mantle.

relative plate velocity

The movement of one lithosphere plate with respect to another.

Hadean Eon

The oldest of the Precambrian eons; the time between the Earth's origin and the formation of the first rocks that have been preserved.

Holocene epoch

The period of geologic time since the last glaciation.

How do we identify a plate boundary

The plate boundaries are the breaks of the plates.

How does the principle of fossil succession help determine relative ages?

The principle of fossil succession relies on two assumptions: no two species are exactly alike, and once a fossil species becomes extinct, it never reappears.Fossil Succession- fossils preserved in lower layers of sedimentary rock are older than those in overlying layers. Specific fossils occurred at specific times in earth history, which allowed for the establishment of a geologic time scale.

radioactive decay

The process by which a radioactive atom undergoes fission or releases particles, thereby being transformed into a new element.

paleomagnetism

The record of ancient magnetism preserved in rock.

seismic belts

The relatively narrow strips of crust on the Earth under which most earthquakes occur.

lithosphere

The relatively rigid, nonflowable, outer 100- to 150-km-thick layer of the Earth, constituting the crust and the top part of the mantle.

Cambrian explosion

The remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period.

geochronology

The science of dating geologic events in years.

Describe the pattern of marine magnetic anomalies across a mid-ocean ridge. How is this pattern explained?

The sea floor magnetic field is layered in stripes of alternating north and south polarities. That tells us the polarity of the Earth while that particular stripe was being formed. This is evidence of a polar reversal because the stripes alternate and do not share the same polarity.

geologic time

The span of time since the formation of the Earth.

paleopole

The supposed position of the Earth's magnetic pole in the past, with respect to a particular continent.

geologic contact

The surface between two distinct geologic units.

Why are transform plate boundaries required on an Earth with spreading and subducting plate boundaries?

Transform boundary- where earthquakes originate

What is a triple junction?

Triple junction is where 3 points of a plate meet.

How does an unconformity develop? Distinguish among the three kinds of unconformities. Which type is pictured here?

Unconformity is the boundary between two different rock sequences representing an interval of time during which new strata were not deposited and were eroded.

What was Wegener's continental drift hypothesis? What was his evidence? Why didn't other geologists accept Wegener's proposal of continental drift, at first?

Wegner's hypothesis was that all the continents drifted apart from each other. He claimed that they were one large supercontinent called Pangaea.His evidence for his claim was that the general shapes of the separate continents and how they can fit together if you arrange them. He noticed patterns in the mountain ranges; when all the continents are together the ranges line up with one another.Other geologists did not agree with Wegener because he had no theory on HOW the continents separated, without that crucial bit of information, the evidence he already had was weak.

Did supercontinents exist in the Proterozoic

Yes, Rodinia and Pannotia

Why are the marine magnetic anomalies bordering the East Pacific Rise in the Pacific Ocean wider than those bordering the Mid-Atlantic Ridge?

because they're older

What may have caused the flooding of the continents during the Cretaceous Period?

climate very warm, super plumes producing large volcanic events

How did the Cambrian explosion of life change the nature of the living world?

complex food chain

What was the Earth's land surface like during the early Paleozoic?

comprised primarily of Laurentia and Gondwana. Lots of epicontinental seas.

How does crust form along a mid-ocean ridge?

magma pushes up and out, spreading the sea crust

What could have caused the K-Pg mass extinction?

meteorite

Phanerzoic Eon

most recent eon, 542Ma to present.

What happens during radioactive decay, and what does a half- life indicate?

radioactive decay: Parent isotopes are changing into daughter isotopes.The half-life of a radioactive substance is the amount of time, on average, it takes for half of the atoms to decay.

Explain the difference between relative plate velocity and absolute plate velocity.

relative- movement of plate A with respect to plate Babsolute- movement of both plates relative to a fixed location in the mantle below the plates

What evidence do we have that the Earth's surface froze during the Proterozoic Eon? What term do geologists use for the globe shown here?

snowball earth

What life forms appeared during the Mesozoic?

turtles, flying reptiles, dinosaurs, earliest ancestors of mammals