Geol Test Flashcards

Terms Definitions
overturned fold
Cirrus clouds:
wispy clouds
sediment 1/16mm - 1/256mm
Köppen group A:
tropical, humid
trees with fan shaped leaves
love waves
side to side motion
• Earthquakes are shallow, more frequent• Generally low magnitudes
K/T Extinction
Cretaceous/Tertiary extinction. Second great extinction. 
25% of all families lost. Including some ocean vertebrates, all marine invertebrates. Terrestrial extinctions include reptile clans like dinosaurs. Terrestrial survivors were turtles, snakes and crocodiles. 
Possible causes include asteroid impact, evidence in Alvarez' theory which has found iridium enrichment 30 times the normal amount in the Cretaceous period clay. Indicating asteroid impact. 
another word for lower mantle
What lifestyle did the earliest vertebrate have?
"O" horizon
the "duff layer"
-surface accumulation of organic matter
-more that 50% is organic matter
A factor that controls the characteristics of metamorphic rocks is composition of the parent rock (true or false)
mass wasting occurs more with...
younger mountains
• Composed of light silicates rich in aluminum. • Comparatively thin outer skin that ranges from 3 km at the oceanic ridges to 70 km in some mountain belts. • Separated into thin oceanic (3.0 gm/cc) and thicker continental crust (2.7 gm/cc)
Glacial drift
The sediments deposited by glaciers.
ability of object to repel electromagnetic waves without altering object or waves (like a mirror)
local lowering of the water table
breakdown of rock at Earth's surface
lava flows
non-explosive, low-water content, low viscosity magma
a sharp peak that remains after cirques have cut back into a mountain on several sides
Ions precipitate out of solution in pore spaces and form the cementing agent that binds sediment in sedimentary rock
______ stress results in a stretching or extension of material.
pluvial lakes
lakes that developed on nearby, non-glaciated areas
saturated zone
the area below the water table
Mud cracks
• sediment is exposed to dry climate, it shrinks and mud cracks form • common in tidal flats, shallow lakes, and desert basins
Losing streams
• Streams that lose water to groundwater
eruption forecasting
volcanic eruptions cannot be predicted years in advance. but bases on geological data, geologists can say how often and how explosively a volcano erupts
enhanced recovery
exploiting the deposit beyond primary and secondary recovery. can extract 40% of original oil by imcreasing permeability.
natural levees
low ridges of flood deposited sediment that form on either side of a stream channel and thin away from the channel
Clay minerals
form at the Earth's surfacesheet silicates, like mica
Winter waves are...
energetic- tall, spread apart waves Waves erode beach sand and carry it offshore
Is it easy for plants to migrate?
not often.
Love wave
wave that exists at Earth's surface; has a side-to-side motion
A group of small fishesof early and middle Paleozoic time with paired eyes, bony armor, and small mouths, but no jaws
Low viscosity:
lave spreads out. Lower viscous lava is higher temperature and has fewer silica chains.
rock avalanche
the very rapid downslope movement of rock and debris
Example of batholith
Sierra Nevada and Southern California Batholith
Arthur Holmes
-One of key developers of radiometric dating-Proposed sea floor spreading as the cause of mid oceanic ridges and the formation of the sea floor
Confuciosornis and Protoavis
Confuciosornis was the earliest bird with a toothless beak, several million years older than Archaropteryx. 
Protoavis was the first disputed bird. 75 million years older than Archaeopteryx. 
lateral erosion
the erosion and undercutting of a stream's banks and valley walls as the stream swings from side to side across its valley floor
hanging wall
the overlying surface of an inclined fault
-makes up 1/3 of Earth's mass
-iron is most abundant mineral by mass
-inner core grows over time, as Earth cools
S waves
shear seismic body waves; do not propagate through liquids
The misconception of biofuels
Biofuel champions assure us that because fuel crops are renewable, they are environment-friendly, can reduce global warming and will foster rural development. But the tremendous market power of biofuel corporations, coupled with the poor political will of governments to regulate their activities, make this unlikely.
lateral moraines
stripes of debris that form along the side edges of the glacier's surface
Basins in Appalachian Mountains:
Paleozoic continental margin prior to formation of mountains; other basins formed along flanks of mountains.
Types of "failure surfaces"
-saturated sand or clay layers
-joints parallel to the land surfaces
-weak sedimentary bedding
-metamorphic foliation
San Franciso Earthquake
- 8.3 magnitude- rippled the ground waves 1 meter high- 20 meters from crest to crest- Destroying buildings at least 20 miles from the fault
Subsolar point
Point at which sun's rays hit at 90º
hot spring
springs in which the water is warmer than human body temperature
1-1 Earth Characteristics
internal heat - interior and surface changesradioactivity - causes internal heat, breakdown of potassium, uranium, and thorium is principal sourceaccretionary heat - inherited from formation of planets, may have melted earlier planets
What is a joint?
fractures in rocks with NO displacement along the fractures
direct effects of recent glaciation
northern and eastern Canada were abraded during growth of the North American ice sheets; soil and sedimentary rock scraped off, underlying crystalline bedrock was scoured; thousands of future lake basins (created great lakes) were gouged out of the bedrock; the midwest was flattened
What are soil profiles?
-The sequence of soil horizons from the surface down to the underlying bedrock
-Vary considerably, and are influenced by such factors as climate, topography, and rock tyoe
Four main branches of geophysics
1. Seismic wave2. Gravity3. Heat flow4. Magnetic field
Substances analyzed in ice cores:
isotopes of hydrogen (deuterium) and oxygen (O-16 and O-18), dust (desert aerosols), and marine aerosols (salts)
What causes subsidence?
The ground sinks when water is pumped from wells faster than natural rechage processes can replace it.
Strong, turbulent rivers and ocean waves can move:
larges clasts; less turbulent currents can only move fine-grained sediment.
Prescribed fires are designed to control
build-up of underbrush that frequently fuels wildfires
Measurement of 18O/16O ratio in CaCO3 fossils is indicator of climate when organism lived....
High 18O/16O-> colder climate Low 18O/16O-> warmer climate
What kind of eggs do amniotes have?
terrestrially adapted (can be either laid as eggs or carried by mother)
Creation of an oil reserve is dependent on (4) features
-a source rock
-a migration pathway
-a reservoir rock
-a trap
Oceanic crust to continental crust convergence causes:
Volcanic ranges ex.) Andes
How do plants adapt to the problem of living in the air (no nutrients in the air)
internal transport system moved nutrients and water around the whole plant.
What forms an extension of Africa's rift system?
the Levant fault or DEAD SEA TRANSFORM
How did early plants begin to deal with desiccation?
they evolved a waxy coating (the cuticle) over the exposed upper surfaces.
What is the historical 1-hour standard for meeting attainment for ground level ozone?
Must exist at less than 125 molecules / 1 billion molecules- must also have no more than 3 exceedances over a consecutive 3 year period at a single monitor
MC: What is the major cause for the movement of tectonic plates?

A)Rapid convection in liquid outer core
B) slow convection in solid mantle over geologic time
C) Earthquakes
D) Volcanoes
B) slow convection in solid mantle over geologic time
barchan dune
compacted clay minerals.
surface of Earth
clay and silt together
mimic artesian aquifers
elevation creates artificial potentiometric surface
pressure drives water through the distribution system
(A metamorphic rock)
-minerals have segregated into bands of one kind of mineral
what facilitates migration
-rock fractures
-ground water
Felsic composition
Rich in silica-Continental crust
pH = ____
-log [H+ concentration]
C-bearing material
bones, shells, wood, etc
a fine-grained deposit of wind-blown dust (silt & clay)
Female Choice
females actively selected their desired mates
Late Paleozoic:
amphibians and early reptiles evolve
consists primarily of highly permeable sand and gravel that allow groundwater to flow easily
• Black in color• Common member of the mica family• Excellent cleavage in one direction• Produces the “glimmering” often seen in beach sand
Continental crust
-Rich in Aluminum(Al) and Silicon(Si)-Lighter
formation of iceburgs; the glacier touches warm water and gets broken
Benioff zones
zone of inlcined seismic activity
who established the principle of original horizontallity
What do roots do?
solve the nutrients problem
Isthmus of Panama
connects North and South America
Lithified till / plowed up material pushed up from a glacier
_____ volcanoes have broad bases and gently inclined slopes.
angular unconformity
contact separates older tilted or folded layered rocks from younger overlying strata
-only found in rocks younger than 420Ma
-black brittle, sedimentary rock
-remains of organic vegetation
Gabbro (Intrusive)
• Phaneritic • Not very common on surface b/c the magma is very fluid and hot (easy to come to surface) • Intrusive equivalent of basalt
Continental rises
gently seaward sloping (0.5 degree) wedges of sediment extending from base of slope to deep sea floor. Ending in abyssal plains at 5km. Lie upon oceanic crust. Sediment deposited by turbitdity & contour currents
Mauna Kea
inactive volcano, highest point in Hawaii (4206 m) had an ice cap during last ice age, erosion by ice not covered by new lava
Longitudinal Profile of a River
Towards the mouth (end)
Gradient flattens
Discharge increases
Grain sizes smaller
Channels describe broad meander belts
a fingerlike ridge of sediment that extends out into open water
active continental margins
-mostly around Pacific Ocean
-leading edge of continent overruns oceanic lithosphere
-accretionary wedges
-narrow continental shelf
-deep-ocean trench
the slow, gradual slipping along a fault zone without major, damaging earth quakes
Three most common fossil fuels
coal, gas and oil
The solid Earth; one of the Earth's basic spheres
water-flux melting
melting that occurs when the addition of water decreases the melting temperature of hot rock (changes composition, leading to change in melting temperature)
Sounds waves:
transmitting sound waves from a ship and timing how long it takes for waves to return; longer return time the deeper the ocean floor.
What is ablation?
The accumulation exceeds loss, the glacial front advances
If ablation increases and or accumulation decreases, the ice front will retreat
Ductile/Plastic deformation
• Changes in shape of rock are permanent and not reversible (like folding)Ex: Silly putty pulled slowly or warm taffy
magma thrown through air, can be mixed with volcanic gases, may be fragments of lava or glass.tuff: a deposit of tephraspatter: basaltic lava droplets, still liquid when it landsPele's tears: drops of lava, quench to glass in mid-air
What are sedimentary deposits?
banded iron formations. chemically precipitated. appears layered. contains iron.
drainage pattern
reveals the nature and structure of the rocks underneath a river
can be used to measure the strength of an earthquake
Charles Lyell
Wrote the first geology text book, stressed importance of slow processes over long periods of time
Galeras Volcano
1993, killed 6 volcanologists & 3 tourists
How is principle of fossil succession used to date rocks?
by telling time
The upper part of a glacier, where the snow and ice are present year-round, is called the zone of ablation (true or false)
What are volcaniclastic sediments?
-Another kind of clastic sediment; distinct because all of the clasts are volcanic in origin
-Because fragments are hot when formed, they are also called pyroclasts
What drives plate motions?
Convective flow in the mantle • Slab-pull• Ridge-push• Convective friction
A state in the U.S. with the fewest lightning deaths in a typical year is:
What kind of bond keeps hydrogen and oxygen atoms together in a water molecule?
Covalent bonds
equilibrium line
marks the highest point at which the glacier's winter snow cover is lost during a melt season
turbidity currents
found at the base of the continental slope; deposit sediments that form deep-sea fans
How deep was this sea at it's deepest?
<200m (~600 ft)
glacial outwash
till deposited by a glacier at its toe may be picked up and transported by meltwater streams that sort the sediment
What is glacial budgeting?
The balance, or lack of balance, between accumulation at the upper end of the glacier, and loss at the lower end
What comprised the Early atmosphere?
Early atmosphere was comprised of Hydrogen and Helium - light elements or not heavy
thrust fault
a reverse fault in which the dip of the fault plane is at a low angle to horizontal
What does the different behavior emitted by oxygen and carbon dioxide in water and air mean for organisms?
the respiration and gas exchange mechanisms need to be different.
What layer is occasionally present beneath the A horizon?
-The E horizon
-Typically grayish in color because it contains little humus and the mineral grains do not have dark coating of iron and manganese hydroxides
-Most common in acidic soils of evergreen forests
What effect did Volcanic eruptions have on earth's early atmosphere?
Volcanic eruptions contributed to CO2, H2O vapor, and N2 and other sulfur bearing gases in earth's atmosphere
What can pumping of wells cause?
drawdown (lowering) of the water table, and a cone of depression in the water table
Pahoehoe lava usually is fed by:
a lava tube. Surface forms small folds.
Lava, extrusive, or volcanic rocks
• When magma comes to surface it is called lava and forms extrusive, or volcanic rocks and has finer crystalsEx: Volcanic (extrusive): Hawaii (basalt) and Cascades (andesite)
discharge (of a stream)
the volume of water that flows past a given point in a unit of time
false (young igneous rocks that contain carbon)
14C dating is effective on old igneous rocks that contain feldspar (true or false)
Over the last 7000 years there has been a
lowering of global average temperature totaling 2°C.
1. gravel 2. sand 3. silt 4. clay
In order of decreasing grain size (largest first), sedimentary grains include:
What is the cause of Earth's magnetic field?
Rapid convection in the liquid outer core
Are patterns formed by currents of air or water preserved?
-Yes - they can be preserved and later exposed on bedding surfaces
-Example - bodies of sand that are moved by wind, streams, or coastal waves are often rippled
<45% SiO2
ropy lava flow
loose powder avalances
Types of foliated rocks
Marine Deposition
*sublittoral: shelf
*Buthynl: slope
* Abyssal: deep ocean
*Hadal: trenches
(supporting evidence for continental drift) evidence from glaciers is on many continents; extent and flow direction evidence makes more sense when the continents are fit together
Giant Tortoises
-different tortoises inhabited different islands although related to mainland tortoise
marine microscopic zooplankton and algae
rocks with flat, wind-abraded surfaces
plate boundaries
where plates come together
eat algae, single-celled with nucleus, heterotrophic
_____ metamorphism occurs adjacent to a pluton when a body of magma intrudes a relatively cool country rock.
contact on plutonic or metamorphic rock overlain by younger sedimentary or volcanic rock
rock with a concentration of metal-rich minerals
• Minerals that do not exhibit cleavage have a fracture• Most common are irregular, concoidal (like glass), fiberous, and splintering.
remains or tangible evidence of ancient life found within rocks
How do glaciers do at sorting?
1-8b Mesosphere
Stronger, more rigid than asthenosphereregion between asthenosphere and core
Georges Cuvier
found excessive extinctions from catastrophes and then new species were created which faught evolution
Renewable energy
Renewable energy is derived from natural resources that can be replenished naturally within a relatively short time frame and with potential to provide energy well into the future
A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of 100 km and in some regions extends as deep as 700 km. The rock within this zone is easily deformed.
all rounded particles corser than 2mm in diameter (the thickness of a US nickel)
What is the most recent geologic era?
Age of the Earth
4.6 Billion Years Old
takes place in the Earth's interior and changes texture, formation of new minerals or both in new rocks
Cinder cones
Very small• Forms scoria, a dark red-brown vesicular fragment • Product of gas rich, basaltic magma• Small 300-700 meters in height, steep slope angle• Frequently occur in groups, normally one time eruptions
Gravity affects...
-Buoyancy of magma-Emergence of gases from solution-Lava flow thickness-Plinian convection columns
Bar that just out into ocean perpendicular to shore. Traps sediment, building up the beach.
Leeching is often seen in ___ climates.
Precambrian shield
a complex of Precambrian metamorphic and plutonic rocks exposed over a large area
secondary (S) waves
shake motion

travels only through solids

slower velocity, greater amplitude than P waves
the point on the earth's surface directly above the focus of an earthquake
grassland soils
very rich in humus, very fertile, excellent for farming
physical geology
a major division of geology that examines the materials of Earth and seeks to understand the processes and forces acting upon Earth's surface from below.
normal polarity
magnetic lines of force leave the earth near the geographic south pole and reenter at the geographic north pole
stacks of rock that are surrouned by several cirques
The transformation of water from a gas into a liquid, and the processes that lead to condensation
Cross cutting relationships
• Younger features cut across older feature
Relative humidity:
ratio of humidity content to capacity of air to hold water (%)
Common Pollutants: Thermal Pollution
-temp increases
-hot water discharge from industrial operations, power plants, abnormal ocean, currents, urban runoff
a strip of sediment that extends from the low-water line inland to a cliff or a zone of permanent vegetation
1-1 Outer planets
Jupiter, Saturn, Uranus, Neptune - giant balls of gas, majestic rings, dozens of small satellites composed of icePluto - small, similar to icy moons
Regression Sequence
indicated sea level fall, coarse grain sediment over fine grain sediment
What is wave refraction?
the bending of a wave
P-wave (Primary Wave)
wave that exists within the Earth's body; high velocity (arrives first); compressional wave; have a back and forth motion (parallel to the direction of wave propagation)
s-wave shadow zone
the zone ≥103° from the epicenter of an earthquake; suggests the outer core is a liquid, careful observations of p-wave refraction patterns indicate inner core is a solid.
Evolution of magma
• One magma may produce rocks of very different compositions• Minerals crystallize in a systematic fashion based on their melting points• During crystallization, the composition of the liquid portion of the magma (melt) continually changes
During an El Nino condition, the trade winds in the Pacific
reverse direction.
steps of strip mining
1. remove topsoil2. remove overburden and pot it in spoil banks3. remove coal (there's a gaping pit)4. reclamation
heat flow
the gradual loss of heat through the Earth's surface
a form of an element thst differs from another form in the number of NEUTRONS in its nucleus
What allows the nutrients and oxygen to get to the roots?
The gas transport system.
baymouth bar
A _____ is a ridge of sediment that cuts a bay off from the ocean.
chemical sediment
can be inorganic - halite - can be organic - coal
SO2 aerosol in stratosphere will..
cause spectacular sunrises & sunsets, produce unsually colored sun and moon, lower average global temp
What are the three Phase of soil
Solids, Liquid, and Gas
By the Ordovician what kind of fish developed?
fish with bony plates
How do artesian wells occur?
Artesian wells are results from an inclined aquifer
Solutions to the soil depletion problem:
wind breaks, terracing, plowing with slop contours
What is runoff?
part of water which is not soaked into the ground, moving downward into bodies of water
What are some uses for evaporite minerals?
-Often mined because they have industrial uses (gypsum; salt)
When the far side of each fault moves to the left/right so that the stike-slip fault is termed?
Left-Lateral or SinistralRight-Lateral or Dextral
Killer Lakes of Cameroon (Lake Nyos)
Africa gas killed all but 4 people
What is sediment like in an alluvial fan?
-Sediments range from coarse, poorly sorted gravel upstream to well-sorted, cross-bedded sand downstream
why does natural air pollution have a low significance in causing human health problems?
Natural air pollution has low significance because- exposure levels are low- sources and human populations are often distant- major source emissions are episodic and transient
What are slow slurry flows called and where do they usually occur?
-The process is known as solifluction, and is common in areas with high rainfall, where soil is thin over bedrock, and in areas where the ground is frozen at depth
What is the zone of soil moisture?
near suface zone within the zone of aeration that has water that is held by molecular attraction to soil particles
What do stomata do when it is too hot or too dry?
They get closed by guard cells that flank the holes
brittle solid
Old Faithful
"hot spring"
Felsic is:
lighter in color.
Type of rock
not layered
partially-decayed animal and plant remains.
flank eruption
eruption from secondary vents
• Sediment turned into sedimentary rock • Compaction from weight of overlying rock• Cementation from precipitation of minerals between sediment grains: calcite, silica, and iron oxide
Double-bars jutting out perpendicular to shore. Build beaches and create harbor entrances.
*increase sea level (deposition: Mudstone on top, sandstone on bottom)
Indonesia, 1883, "The Scream" painting, sky was all red and stuff, side collapsed causing a tsunami
energy levels
spherically shaped negatively charged zones that surround the nucleus of an atom
Which is larger: sand or clay?
dissolved load
dissolved ions in a stream
species defined and based on morphologic features that can be recognized in fossils
Monocline fold
Step-like folds in horizontally sedimentary strata
DMS units
Degrees, minutes, seconds of arc
load structure
graded bedding with flame structure
A) Shale
B) Sandstone
C) limestone
D) Dolostone
E) Granite
F) Basalt
F) Basalt
measure of earthquake size; often reported using the Richter magnitude scale
karst topography
dissolution of bedrock by groundwater leads to a unique irregular type of terrain
patterned ground
landscape created by annual thawing and refreezing splits the ground into pentagonal or hexagonal shapes
a failed rift filled with continental sediment
Accretionary prisms:
most terranes are accreted to continents via subduction, where accretionary prisms develop during the subduction process.
mantle plumes
What is believed to initiate continental rifting?
Who claimed that continents plowed through the oceanic crust?
Alfred Wegener.
amount of material a stream can carry
Causes of Mass extinction
1.      Plate tectonics/ volcanic 2.      Climate change 3.      Ocean currents change 4.      Biological 5.      Impacts; cosmic radiation
short-term, day to day conditions of atmosphere
bridges of rock left above openings eroded in headlands or stacks by waves
minerals grains can be destroyed as their constituent atoms become rearranged in a solid statecaused by heat and pressure
limestone is easily dissolved by water flowing through it, leaves caverns of water, water leaves, caves weakens and roof collapses
Whatdoes deflation cause?
blowouts (shallow depressions) and desert pavement ( a surface of coarse pebbles and cobbles)
mechanical weathering
type of weathering more dominant in deserts because of lack of water (makes limestone resistant); shale usually erodes more quickly
"Bk" horizon
calcium carbonate (CaCO3) , from dust or chemical weathering
When soil is ______ with water, pore pressure increases.
What is the compositions of chemical sedimentary rocks usually called?
-Monomineralic composition
great lakes formation
shallow basins formed behind moraines as glaciers melted back
The elevation change of a stream per unit of horizontal distance is its ____________.
Modified Köppen scheme:
empirical system of climate regions classification based on temperature & precipitation
Acids dissolve ___ in the soil, which is then free to poison aquatic organisms.
shear stress
due to forces parallel to one another, but in opposite directions along a discrete surface such as a fault
Which rock corresponds to the mineral &quot;CLAY&quot;?

A) Shale
B) Sandstone
C) limestone
D) Dolostone
E) Granite
F) Basalt
A) Shale
Sedimentary rock
rocks formed from sediments at low temperature
What are the two lineages of tetrapods?
Amphibians and Amniotes
metallic bond
a chemical bond present in all metals that may be characterized as an extreme type of electron sharing in which the electrons move freely from atom to atom
As material move farther from source area, sediment gets:
smaller and rounder.
is a body of water that carries rock particles and dissolved ions and flows down slope along a clearly defined path, called a channel.
Ropey Lava aka "pahoehoe"
Lava flow like "honey"produce rope like folds
felsic rock
>63% silica, very little FeO and MgO, many light colored mineralsintrusive: graniteextrusive: dacite and rhyolite
If pH = 4, H+ concentration = ___.
10^-4 M
continental rise
a wedge of sediment that extends from the lower part of the continental slope to the deep sea floor
decompression melting
melting caused just by a decrease in pressure
why are fossils rarely preserved?
because most organisms dont have bones/shells tat are durable/dont decay and usually have to be buried quickly to be preserved as fossils
What are common environments for the deposition of sediment of land?
-Stream channels and floodplains
-Lakeshores and lake bottoms
-The margins of glaciers
-Areas where the wind is intermittently strong (beaches and deserts)
what is Iapetus Ocean?
- forerunner to the Atlantic- closed by Africa
what is the raw material for nuclear weapons and dirty bombs?
plutonium (causes radiation)
Carrying capacity
the ability of a system (or the whole earth) to sustain its population in reasonably healthy and comfortable conditions
(3) conditions for glaciers to form:
-local climate must be sufficiently col that winter snow doesnt melt in summer
-sufficient snowfall for large amount to accumulate
-slope of surface must be gentle enough that snow doesnt slide away
Mudpots are formed by?
when a trickle of water reaches the surface, strong acids turn the soil into bubbling mudpots
theory of glacial ages
states that at times in the past, colder climates prevailed during which much more of the land surface of earth was glaciated than at present
After Carboniferous, what happens to the diversity of plants?
it plateaus until the mesozoic to reach today's values.
At a bend in a river, _____ occurs on the outside of the bend and _____ occurs on the inside of the bend.
A. erosion...deposition
B. deposition...erosion
C. erosion...erosion
D. deposition...deposition
What are the different types of Gas Volume Meters?
- Spirometer- displacement Bottle- soap-bubble meter- mercury-sealed piston- roots meter- wet test meter- dry gas meter
Where is a beautiful place to find this chemistry?
The White Cliffs of Dover, England
Which of these is not a fossil fuel?
A. Uranium <---
B. Oil
C. Natural gas
D. Coal
What are some common features of karst topography?
irregular terrain, sinkholes, and the striking lack of surface drainage,
when the dinosaurs lived the coast of N.A. laid where?
- along the present Continental Divide - as a broad continental shelf like that of today's eastern seaboard
what are Island Acrs and what do they do?
- curved lines of volcanic islands- they rise where two oceanic plates collide
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