Historical Geology Exam #2 Study Guide

meteors

"shooting stars"- the glow comes from small particles of rock from space being heated as they enter Earth's atmosphere

ocean-to-continent subduction

An oceanic plate is subducted beneath a continental plate, forming a trench adjacent to a continent, and volcanic mountains along the edge of the continent; Example: Peru-Chile Trench adjacent to the western coast of South America and the Andes Mountains

ocean-to-ocean subduction

An oceanic plate is subducted beneath another oceanic plate, forming a deep-sea trench, with an associated basaltic volcanic island arc; Examples: Marianas Trench adjacent to Mariana Islands, Aleutian Trench adjacent to Aleutian Islands, Java Trench adjacent to Java, Sumatra, and Sunda Islands in the Indonesian region.

magma ocean

If Earth experienced heating and partial melting, it may have been covered by an extensive ____ ____ in the Archean.

Dopler effect

If object is moving toward you, the wavelengths are compressed resulting in high pitched sound or shorter wavelengths; If object is moving away, the wavelengths are elongated resulting in low pitch or shorter wavelengths

red shift

In 1914, W.M. Slipher first noted that galaxies displayed this; their light is shifted toward the red (or long wavelength) end of the spectrum which indicates that the universe is expanding

iron meteorites

Iron-nickel alloy; Coarse-grained intergrown crystal structure (Widmanstatten pattern); About 5% of all meteorites

jovian planets

Jupiter, Saturn, Uranus, Neptune; Large; Low density (0.7 - 1.5 g/cm3); Gaseous

oxidized iron

Lack of _____ ___ in the oldest sedimentary rocks. (Instead, iron combined with sulfur to form sulfide minerals like pyrite- happens only in anoxic environments.)

subduction zones

Felsic crust formed in _____ ____ where descending slabs of crust partially melted- the early-melting, less dense components of the melt rose to the surface where they cooled to form continental crust.

differentiation

Heat from impacts led to melting and _______(or segregation of materials of different density; low density materials rose and high density materials sank).

komatites

Magma cooled to form these ultramafic rocks composed mainly of olivine and pyroxene which formed Earth's Archean crust

basement rocks

Precambrian rocks are often called _______ ___because they lie beneath a covering of fossil-bearing sedimentary strata.

P-waves

Primary, pressure, push-pull; Travel fastest of the seismic waves (6 km/sec in crust; 8 km/sec in uppermost mantle); Travel through solids and liquids

outer core

S-waves cannot pass through, therefore we know it is liquid (molten); Composition: Molten Fe (85%) with some Ni- may also contain lighter elements such as Si, S, C, or O; Convection in liquid outer core plus spin of solid inner core generates Earth's magnetic field- also evidence for a dominantly iron core

comets

made of frozen gases, ice, and dust

moon

may have formed as a result of an impact of a large body with Earth about 4.4 billion years ago

shields

most extensive exposures of Precambrian rocks are in geologically stable regions of continents

strike-slip fault

movement is horizontal

metazoans

multicellular animals with various types of cells organized into tissues and organs; first arrives in the late Proterozoic eon (about 630 million years ago)

eukaryotes

new form of life to appear during the mid proterozioc eon

prokaryotes

oldest evidence of life in Archean eon; Microscopic cells associated with stromatolites; Similar to cyanobacteria living today, which produce oxygen; Fossiliferous chert bed associated with the Apex Basalt; Found in Warrawoona Group, Pilbara Supergroup, western Australia 3.460-3.465 billion years

sedimentation

on and around the craton consisted of shallow water clastic and carbonate sediments deposited on broad continental shelves and in epicontinental seas; brought about by Wilson cycles

outgassing

the release of water vapor and other gases from the Earth through volcanism

anticline

upfolds when the upper part of the fold is eroded away, the oldest rocks are in the center of the fold, and the youngest rocks are on each side; the rocks dip (or slope) away from the central axis of the fold

plates

The Earth's surface or lithosphere is divided into _____ (7 large and 20 smaller).

ediacara

There was the first evolutionary radiation of metazoans, called _____, at the end of the Proterozioc eon which included jellyfish, sea pens, segmented worms, and a few shells.

banded iron formations

Widespread outcrops of ____ __ ____ were deposited 2.5 - 2 billion years ago; laid down before oxygen was present in the atmosphere, algae binds torn to oxygen waste products; iron oxides sank to bottom of oceans; banded due to expanding/ reducing/ seasonality in the algae's environment; 90% of world's iron ore

global climate

____ _____ became more modern in the Proterozioc eon, so they include glaciations.

Continental

______ crust developed after the initial mafic to ultramafic crust and is sialic or felsic (such as granite) and dominated by light-colored minerals such as quartz and feldspar- began forming around 4.4 billion years ago.

Proterozoic

______ eon brings more modern plate tectonics that include mountain building

sun

a star; Composition: about 70% hydrogen and 27% helium, and 3% heavier elements. Size: About 1.5 million km in diameter; Contains about 98.8% of the matter in the Solar System; Temperature: may exceed 20 million oC in the interior

striations

grooves on the bedrock

Huronian glaciation

in Canada; recorded Ice age in Paleoproterozoic, about 2.4-2.3 million years ago

Canadian Shield

in North America; mostly igneous and metamorphic rocks; few sedimentary rocks- overlying sedimentary rocks were scraped off by glaciers during last Ice Age

cratons

large portions of continents which have not been deformed since Precambrian or Early Paleozoic time

rodinia

late in the Proterozoic, the continents became assembled into this supercontinent; broke up during the neoproterozioc eon; lasted 350 million years- it's breaking up formed the Pacific ocean

tillites

layers of glacial deposits

terrestrial planets

(Earth-like): Mercury, Venus, Earth, Mars; small; Dense (4 - 5.5 g/cm3); Rocky + Metals

carbonate rocks

(limestones and dolostones) appear in the stratigraphic record at about the same time that red beds appear- indicates that carbon dioxide was less abundant in the atmosphere and oceans so that the water was no longer acidic

oceanic continental

2 types of crust today: Dense, mafic (magnesium- and iron-rich) _____ crust dominated by basalt Less dense, sialic (silicon- and aluminum-rich) _____ crust dominated by granite

Australia

A 3.46 by old fossil soil zone (or paleosol) associated with an unconformity in the Pilbara region of _____ indicates that Archean continents stood above sea level- represents the oldest land surface known, and provides evidence that subaerial weathering, erosion, and soil formation processes were at work in the Archean.

Stromatolites

An organo-sedimentary structure built by photosynthetic cyanobacteria or blue-green algae- they are not true fossils; form through the activity of cyanobacteria in the tidal zone -the sticky, mucilage-like algal filaments of the cyanobacteria trap carbonate sediment during high tides; found in carbonate sedimentary rocks and in cherts which replace carbonates- more abundant in Proterozoic rocks than in Archean rocks; 3.5 billion years ago

carbonate rocks

Archean sedimentary sequences lack _____ ___ but contain abundant chert, presumably due to the presence of an acidic, carbon dioxide-rich atmosphere.

stony-iron meteorites

Composed partly of Fe, Ni and partly of silicate minerals, including olivine (like Earth's mantle); About 1% of all meteorites- least abundant type

oxygen

Earth's first, primitive atmosphere lacked free _____.

Canada

One of the oldest dated felsic Earth rocks is the 4.04 billion year old Acasta Gneiss from northwestern _____.

density elasticity

Seismic wave velocity depends on the _____ and _____ of rock.

platforms

Stable regions of the craton where shields are covered by sedimentary rocks

fusion

Sun's energy comes from _____, a thermonuclear reaction in which hydrogen atoms are fused together to form helium, releasing energy.

photosynthesis

The atmosphere transitioned to oxygen-rich during the Proterozoic eon because of ______.

photochemical dissociation

The breaking up of water molecules into hydrogen and oxygen in the upper atmosphere caused by ultraviolet radiation from the Sun (a minor process today)

Archean sedimentary

The earliest evidence of life occurs in ____ _______ rocks.

stromatolites prokaryotes

The early Proterozioc eon was similar to the late Archean eon- _____ and _____ life forms present

mafic

The first ____, oceanic crust formed about 4.5 billion years ago by partial melting of rocks in the upper mantle.

Australia

The oldest zircon grains are 4.4 billion years old found in quartzite (metamorphosed sandstone) in western _____; Sedimentary structures in the quartzite resemble those in modern stream deposits, these rocks are interpreted as fluvial (river) deposits and were derived from the weathering of granitic rocks (some of the earliest continental crust), and deposited above sea level, indicating the presence of both liquid water and continental crust by 4.4 billion years ago.

photosynthesis

The process by which photosynthetic bacteria and plants produce oxygen (major process)

anaerobic metabolism

The simplest living organisms have an ______ ______- They are killed by oxygen- Includes some bacteria (such as botulism), and some or all Archaea, which inhabit unusual conditions.

orogenies

associated with mountain building; first show evidence of Wilson cycles- opening and closing of ocean basins

Varangian glaciation

at the end of the Proterozoic eon; marked by widespread glacial deposits; Neoproterozoic, 850-600 million years ago, "snowball Earth"

precambrian

covers approximately 4 billion years (and 87%) of Earth history; divided into the Archean and Proterozoic eons

Lorentia

crust accretes around Archean core forming North America and Greenland

hydraulic cycle

evaporation and precipitation, powered by the sun and by gravity

red beds

sedimentary rocks with iron oxide cements, including shales, siltstones, and sandstones, appear in rocks younger than 1.8 billion years old in the Proterozoic Eon, after the disappearance of the BIF.

Achondrites

stony meteorites without chondrules, resembling basalt

volatiles

substances easily driven off by heating

subduction zones

The descending part of a convection cell is associated with ______ ___.

convergent

The plates move toward one another and collide; Crust is destroyed as one plate is pushed beneath another; boundaries form continental collisions and subduction zones

gabbro

coarse grained equivalent of basalt; cooled slowly (about 6 km thick)

drum recorders

Earthquakes are recorded on ____ _____ connected to seismographs.

seismic waves

Energy moving outward from the focus of an earthquake travels in the form of _____ ____.

convection cells

Large-scale thermal _____ ___ in the mantle may propel the tectonic plates, which are floating on the asthenosphere; they transfer heat in a roughly circular pattern- Hot material rises and cool material sinks; Heat in the mantle is probably the result of radioactive decay

mantle

(2885 km thick); Average density is 4.5 g/cm3, indicating it is made of rock, not metal; composition based on studies of rock brought up by volcanoes, from density calculations, and composition of stony meteorites: Peridotite (Mg Fe silicates, olivine), Kimberlite (contains diamonds), Eclogite; not uniform, has several concentric layers with differing properties

Canada

Earth's oldest rocks are found in _____ (4.04 billion years old)

divergent

The plates diverge or move away from each other; New crust is generated between the diverging plates(tensional stress); Rifting or spreading or pull-apart occurs. Rifting may occur in either oceanic or continental crust; Rift zones tend to have normal faults and intrusions of igneous rock coming up from below, which forms new crust

transform

The plates slide horizontally past each other; Crust is neither produced nor destroyed- cut across and offset the mid-ocean ridges; a natural consequence of horizontal spreading of the seafloor on a curved globe; cut the Mid-Atlantic Ridge and other midoceanic ridges

slab pull

The process when near subduction zones, the oceanic crust is cold and dense, and tends to sink into the mantle, pulling the rest of the oceanic plate behind it

galaxy

an aggregate of stars, planets, dust, and gases

continental crust

averages about 35 km thick; 60 km in mountain ranges); Granitic composition; Less dense (about 2.7 g/cm3).

pillow basalts

basalts that erupted under water (about 2 km thick)

refraction

bending of waves

discontinuities

boundaries between the layers of the Earth

isostasy

buoyancy and floating of the Earth's crust on the mantle

meteorites

chunks of rock from the Solar System that reach the Earth's surface which include fragments of asteroids, moon rock, planets (such as Mars)

thermal plumes

concentrated areas of heat rising from near the core-mantle boundary

exotic terrane

fault-bounded areas with different structure, age, fossils, and rock type, compared with the surrounding rocks

guyots

flat-topped sea mounts (erosion when at or above sea level)

Wilson cycle

plate tectonic model for the opening and closing of an ocean basin over time consisting of the following stages: opening of a new ocean basin at a divergent plate boundary, Sedimentary deposits at this stage include quartz sandstones and shallow-water platform carbonates, grading into deeper water shales with chert horizons; The expansion of the ocean basin as seafloor spreading continues and subduction begins- Graywacke, turbidites, and volcanic rocks are deposited, along with mélange, thrust faults, and ophiolite sequences near the subduction zone; A final stage of continental collision associated with conglomerates, red sandstones, and shales, deposited in alluvial fans, rivers, and deltas as older seafoor sediments are uplifted to form mountains, and eroded

hot spots

present on the Earth's surface above a thermal plume

colors of the spectrum

red, orange, yellow, green, blue, indigo, violet

solar system

the Sun and the planets, moons, asteroids, comets and other objects that orbit it

declination

the angle between where a compass needle points (magnetic north) and the true geographic north pole (axis of the Earth)

inclination

the angle of the magnetic field with respect to the horizontal (or the dip of the magnetic field); At the north magnetic pole, the inclination is 90 degrees (vertical); At the equator, the inclination is zero degrees (horizontal)

gravity anomaly

the difference between the calculated theoretical value of gravity and the actual measured gravity at a location

seismograph

an instrument that records earthquakes

polar wandering

when ancient magnetic pole positions are plotted on maps, we can see that they were in different places, relative to a continent, at different times in the past- poles have not moved, but the continents have moved

oceanic crust

(5 - 12 km thick); Basaltic composition; More dense (about 3.0 g/cm3); has a layered structure consisting of a thin layer of unconsolidated sediment covers basaltic igneous rock (about 200 m thick), pillow basalts (about 2 km thick), and then gabbro (about 6 km thick)

ophiolite suite

A distinctive assemblage of rocks consisting of deep-sea sediments containing marine microfossils, submarine basalts (pillow lavas), metamorphosed mantle rocks such as serpentinized peridotite

melange

A complexly folded jumble of deformed and transported rocks

accretionary prism or wedge

A highly contorted and metamorphosed body of rock that is compressed or accreted onto the margin of the continent; Sediments scraped off the descending plate are added to the accretionary prism

chain

As the plate moves across the hot spot, a ____ of volcanoes forms; The youngest volcano is over the hot spot; The volcanoes become older away from the site of volcanic activity; Example: The Hawaiian island chain

4.6

Based on radiometric dates of moon rocks and meteorites, the Solar System is about ___ billion years old.

nebular hypothesis

Cold cloud of gas and dust contracts, rotates, and flattens into a disk-like shape; Roughly 90% of mass becomes concentrated in the center, due to gravitational attraction; Turbulence in cloud caused matter to collect in certain locations, clumps of matter begin to form in the disk, accretion of matter (gas and dust) around clumps by gravitational attraction, clumps develop into protoplanets; Solar nebula cloud condenses, shrinks, and becomes heated by gravitational compression to form Sun; Ultimately hydrogen (H) atoms begin to fuse to form helium (He) atoms, releasing energy (heat and light). The Sun "ignites"; The Sun's solar wind drives lighter elements outward, causing observed distribution of masses and densities in the Solar system; Planets nearest Sun lose large amounts of lighter elements (H, He), leaving them with smaller sizes and masses, but greater densities than the outer planets. Inner planets are dominated by rock and metal; Outer planets retain light elements such as H and He around inner cores of rock and metal. Outer planets have large sizes and masses, but low densities.

Carbonaceous chondrites

Contain about 5% organic compounds, including amino acids (building-blocks of proteins, DNA, and RNA); May have supplied basic building blocks of life to Earth; Contain chondrules

paleomagnetic evidence

Magnetic reversals have occurred relatively frequently through geologic time; Recently magnetized rocks show alignment of magnetic field consistent with Earth's current magnetic field; Magnetization in older rocks has different orientations (as determined by magnetometer towed by ship); Magnetic stripes on the seafloor are symmetrical about the mid-ocean ridges; The magnetic stripes on the seafloor, and their symmetry about the mid-ocean ridge, verified seafloor spreading

blueschists

Metamorphic rocks associated with subduction zones commonly contain blue minerals (glaucophane and lawsonite) which indicate metamorphic conditions of high pressures but relatively low temperatures

ordinary chondrites

Most abundant type of meteorite; About 4.6 billion years old; May contain chondrules

dip-slip faults

Movement is vertical; one side moves up and the other side moves down

meteorites

Much of our knowledge of the Earth's earliest history comes from indirect evidence - _____.

shape of coastlines paleoclimactic evidence fossil evidence distribution of present day organisms geologic similarities rift valleys evidence for subsidence in oceans, paleomagnetism and polar wandering curves

Name the evidence for the theory of plate tectonics: (9 main points)

surface waves

Often referred to as L-waves or long waves Complex motion: Up-and-down and side-to-side Slowest; Causes damage to structures during an earthquake

milky way

Planet Earth orbits the Sun, a dwarf star, that belongs to the ____ ___ galaxy.

S-waves

Secondary, shaking, shear, side-to-side; Slower seismic waves (3.5 km/sec in crust; 5 km/sec in upper mantle km/sec); Travel through solids only

denser

Seismic waves travel faster in ____ rock.

basins

Similar to syncline, but with circular outcrop pattern; Rock layers are down-folded to resemble a stack of soup bowls; When the upper part of the basin is eroded away, the youngest rocks are in the center, and the oldest rocks are around the edges; the rocks dip toward the center of the basin.

microcontinents

Small pieces of continental crust surrounded by oceanic crust; Examples: Greenland, Madagascar, the Seychelles Bank in the Indian Ocean, Crete, New Zealand, New Guinea

inner core

Solid Fe (85%) with some Ni; solid because the enormous pressure prevents the molecules from moving; slightly larger than the Moon

precambrian

The Archean and Proterozoic Eons comprise the ______, which spans 87% of the geologic time scale.

steady-state cosmology

The Universe will continue to expand forever; new matter is formed in the spaces between galaxies at about the same rate that the older material is receding; Density of matter in the Universe remains relatively constant

ridge push

The process when the crust is heated and expands over a mid-ocean ridge spreading center (where hot material is rising from below) and the crust tends to slide off the thermal bulge, pushing the rest of the oceanic plate ahead of it

triple junction

The process when the lithosphere expands and domes upward, above a thermal plume and the uplifted area splits into three radiating fractures; Rifting occurs, and the three plates move outward away from the hot spot

rifting

The rising part of a convection cell is associated with ____ (mid-ocean ridge or continental rifting).

suture zone

The zone of convergence between the two continental plates; marked by intense folding, faulting, metamorphism and igneous intrusions; Examples: Himalaya Mountains, Ural Mountains, Appalachian Mountains

Australia

There are even older mineral grains- Sand-sized zircon grains in metamorphosed sedimentary rocks from _____ are 4.4 billion years old.

curie

When the lava cools to a certain temperature, known as the ____ point, the crystals become magnetized and aligned with Earth's magnetic field.

p-wave shadow zone

Where no P-waves are received by seismographs; Makes a ring around the globe; Smaller than the S-wave shadow zone.

s-wave shadow zone

Where no S-waves are received by seismographs; Extends across the globe on side opposite from epicenter (from 105o); S-waves cannot travel through the molten (liquid) outer core; Larger than the P-wave shadow zone.

radius

____ of earth: 6370 km

diameter

_____ of earth: 12,740 km

monocline

a bend in otherwise horizontal strata

big bang

a big explosion that created Earth 15-18 billion years ago; marked the instantaneous creation of all matter in the Universe

fault

a crack in the Earth's crust along which movement has occurred

thrust fault

a low-angle reverse fault

syncline

down folds; when the upper part of the fold is eroded away, the youngest rocks are in the center of the fold, and the oldest rocks are on each side; the rocks dip toward the central axis of the fold

continental collisions

form mountain belts with folded sedimentary rocks, and a central area of metamorphic rocks and granitic igneous intrusions; Slabs of continental crust may ride up over one another

normal fault

hanging wall moves down relative to the footwall

reverse fault

hanging wall moves up relative to the footwall

Benioff zones

inclined zones of earthquake foci which dip at approximately a 45o angle, near a deep-sea trench

asthenosphere

low velocity zone at 100 - 250 km depth in Earth (seismic wave velocity decreases); Rocks are at or near melting point; Magmas generated here; Solid that flows (rheid); plastic behavior; Convection in this layer moves tectonic plates

subduction

occurs where an oceanic plate is pushed beneath another plate, forming a deep-sea trench; The rocks and sediments of the downward-moving plate are subducted into the mantle, where they are heated, Partial melting occurs, producing molten rock which rises to form volcanic island arcs, or to become incorporated into the crust and upper mantle as intrusive igneous rocks

lithosphere

outermost 100 km of Earth; Consists of the crust plus the outermost part of the mantle; Divided into tectonic or lithospheric plates that cover surface of Earth

Mohorovicic discontinuity

separates the crust from the mantle

Gutenberg discontinuity

separates the mantle from the core

dome

similar to anticline, but with circular outcrop pattern; Rock layers are up-folded to resemble a stack of baseball caps or inverted soup bowls; When the upper part of the dome is eroded away, the oldest rocks are in the center, and the youngest rocks are around the edges; the rocks dip away from the center of the dome

mid-ocean ridges

sites of seafloor spreading with the following characteristics: high heat flow, seismic wave velocity decreases at the ridges, due to high temperatures, a valley is present along the center of ridge, volcanoes are present along the ridge, earthquakes occur along the ridge

chondrules

spherical bodies that solidified from molten droplets thrown into space during Solar System impacts

archean eon

the oldest unit on the geologic time scale. It began 4.6 billion years ago and ended 2.5 billion years ago; lasted for 2.1 billion years (2,100,000,000 years)

focus

the place within the Earth where the rock breaks, producing an earthquake

epicenter

the point on the ground's surface directly above the focus

seismogram

the record of the earthquake produced by the seismograph

earthquake

vibration of the Earth produced by the rapid release of energy