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148 Cards in this Set
- Front
- Back
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What three influences change the local seafloor topography?
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erosion, sedimentation, and coral reef formation
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How is the inside of the Earth heated?
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by radioactive decay
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What properties does the core have?
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It is mainly iron and nickel, with a solid inner core and a liquid outer core.
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What are the layers of the earth, from the center to the surface?
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core, mantle, lithosphere
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What properties does the mantle have?
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It is half as dense as the core, and its outer layer is the plastic (glass-like) asthenosphere.
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What properties does the lithosphere have?
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It is 100 km thick, rigid, less dense than the asthenosphere, has oceans and continents on top of it, forming lithospheric plates.
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What are the two types of crust?
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oceanic and continental
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What are the differences between continental and oceanic crust?
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continental crust is lighter and thicker, made of granite, while oceanic crust heavier and thinner, made of gabbro
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What occurs at the boundary of continent and ocean?
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continental shelf (extension of continent underwater), steep continental slope, and then trench or continental rise
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What are the two types of deep ocean floor?
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abyssal plains and abyssal hills
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What is the boundary between the continental crust and the upper mantle called?
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moho
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What properties does the hydrosphere have?
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Made of oceans and freshwater lakes, it covers 70% of the earth's surface.
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How deep can scientists drill?
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a few kilometers
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How is Earth's interior studied?
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by looking at volcanic rocks, meteorites, and earthquake energy transmission
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What is computer tomography?
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using computers to calculate the densities and states of layers within Earth, including localized "mountains" and "valleys" between core and mantle
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What causes lithospheric plate movements?
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convection in the mantle
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What is thought to cause the upwelling and downwelling of mantle material?
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Heating of lower mantle material causes it to rise, and cooling of upper mantle material causes it to fall.
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What heats the interior of the Earth?
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radioactive decay
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What are the two types of mantle circulation hypothesized?
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shallow circulation to 650 km deep and deep circulation to 3000 km to the surface of the core
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What evidence supports mantle circulation models?
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computer tomography of hot spots and sinking lithospheric plates
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Are lithospheric plates primarily pulled or pushed?
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pulled
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Where do hot spots originate?
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deep and hot near the bottom of the mantle
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How many major lithospheric plates are there?
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seven
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What are the major lithospheric plates?
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Pacific, Eurasian, African, North American, South American, Indo-Australian, and Antarctic
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What characterizes plate movement at plate edges?
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short, rapid movements, felt as earthquakes
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What is comparable to the rate of plate movement?
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the rate of human fingernail growth
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How fast to plates move on the whole?
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a few centimeters per year
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When was Pangaea?
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about 225 million years ago
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What studies indicate the relative motions of fragments of Pangaea?
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rocks (directions), fossils (where), and sediments (how fast)
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What first happened to Pangaea?
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It split into Laurasia (North America and Eurasia) in the north and Gondwanaland (everything else) in the south.
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Which was biggest, Laurasia or Gondwanaland?
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Gondwanaland
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What happened before Pangaea?
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probably the formation and breaking up of supercontinents to make around 10 cycles
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How long do hotspots last in the same spot?
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tens or hundreds of million years
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What are two large examples of hotspots?
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Hawaii and Iceland
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What effect did the Hawaiian islands have on the Pacific ocean floor?
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It made the vicinity sink to create a moat-like region, and the area around that to rise.
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What happens to volcanic hotspot islands formed over time?
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They spend some time over the hotspot, then migrate away, erode, and eventually become seamounts.
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Why is Iceland so big, if it is formed by a hotspot?
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It spreads out due to the mid-Atlantic ridge.
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What are the three ways two plates can interact?
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They can converge, diverge, or slide past each other.
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What happens in the mantle to cause convergent plate boundaries?
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downwelling
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What happens at convergent boundaries to the submerged plate?
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It sinks into the asthenosphere.
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What are the types of convergent plate boundaries?
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continental (continent-ocean), oceanic (ocean-ocean), and continental collision (continent-continent)
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What happens in the mantle to cause divergent plate boundaries?
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upwelling
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What happens at continental divergent boundaries?
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new oceanic crust is formed in the middle
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What happens at oceanic divergent boundaries?
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a mid-ocean ridge is formed
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What are the types of divergent plate boundaries?
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oceanic (ocean-ocean) and continental (continent-continent)
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What is a boundary between three plates called?
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a triple junction
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What are the types of triple junctions?
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stable and unstable
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What happens at stable triple junctions?
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Three divergent plate margins intersect and the location remains constant.
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What happens at unstable triple junctions?
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Three convergent plate margins intersect, and the location moves while plates are submerged.
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As oceanic crust submerges, what happens to the sediments and sedimentary rock?
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It is scraped off due to the low density, and forms an accretion wedge landward of the trench.
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How do volcanoes form?
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As oceanic crust submerges, it is heated, and since it contains lots of water and has a lower melting point, it melts and rises to the surface to be spewed out.
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What are oceanic plateaus?
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small seafloor areas about a kilometer above the surrounding ocean floor
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What are oceanic plateaus made of?
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seafloor volcanoes, old volcanic ridges, or continental crust fragments
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What happens when oceanic plateau areas enter a subduction zone?
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They do not sink, and rather build up on the continental crust, forming exotic terranes.
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What are exotic terranes?
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lower terrain at a continental convergent boundary that "welds" to the continent
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In oceanic convergent boundaries, which plate is submerged?
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the denser one, so the colder one, so the older one
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What happens to the sediments on a submerging plate in an oceanic convergent boundary?
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They accumulate on the nonsubmerging plate, just like a continental convergent boundary.
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What are sedimentary arc islands?
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buildup to the surface of sediments at an oceanic convergent boundary
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What are magmatic arc islands?
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volcanic islands formed from the rising of subducted oceanic crust at oceanic convergent boundaries
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What determines the distance from the plate boundary to the line of volcanoes in a convergent boundary?
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the angle of descent of the submerged plate
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What is a back-island basin?
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a lagoon between the subduction volcanoes and the mainland continental plate
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How do back-island basins form?
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The subduction happens faster than the plates converge, making the nonsubmerging plate stretch and thin, sometimes even creating new oceanic crust.
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What are examples of oceanic convergent margins?
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Indonesia, the Mariana Islands, the Aleutian Islands, and Japan
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Where are most oceanic convergent margins?
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the Pacific
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Where are most continental convergent margins?
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the Pacific
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Which oceans are growing or shrinking?
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The Pacific is shrinking, and the Atlantic and Indian oceans are growing.
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How old is the oldest seafloor sediment?
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170M years
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Why do continental collision margins form mountains?
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Neither plate is dense enough to sink into the asthenosphere, so they rise.
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When were most continental collision margins?
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around the formation of Pangaea
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What are examples of continental collision margins?
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the Himalayas, between Africa and Eurasia, the Urals, and the Appalachians
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When did India and Asia first collide?
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20 million years ago
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Why was the India-Asia collision so violent?
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India was moving very quickly before the collision.
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When did Africa and Eurasia first collide?
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200 million years ago
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What are the result of the collision between Africa and Eurasia?
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the Alps, and Balkan and Turkish earthquakes
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What fills the gap between divergent plates?
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upwelled magma
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What is seafloor spreading?
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the rising of magma from volcanes in the mid-ocean ridge, building the ridge
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What shape do the mid-ocean ridges take on and where are they?
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similar to the surrounding coastlines in the center of the ocean
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What are two other names for the mid-ocean ridge?
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oceanic ridge or rise
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Which crust is hotter, newer or older?
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newer
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Why is the mid-ocean ridge higher up than the abyssal plains?
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The crust in and around the ridge is less dense than the crust on each side.
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What is a central rift valley?
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a steep basin in the middle of the mid-ocean ridge, the gap between the two plates
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What are the dimensions of a central rift valley?
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25-50 km wide, 1-2 km deep
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Why does the East Pacific Rise lack a central rift valley?
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It spreads very fast, which makes it very broad, removing the valley.
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Why are underwater oceanic ridge volcanoes relatively tame?
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The rising magma has no sediments or water; water carries heat away over a large volume; the high pressures prevent evaporation.
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What characteristics do oceanic ridge volcanoes have in comparison to plate boundary volcanoes?
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They are probably around as frequent and big, but buffered by the water when they are underground.
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Where is the largest lava flow in human history?
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the East Pacific Rise
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What are two locations where unseen volcanic activity takes place?
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the East Pacific Rise and Juan de Fuca Ridge
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What makes convection in the mantle change?
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the varying rates of heat conduction within Earth
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What is the first step in a continental divergent boundary?
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Magma rises from the asthenosphere and heats the continent, causing it to rise.
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What is the second step in a continental divergent boundary?
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The continent splits apart, perhaps unevenly.
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What is the last step in a continental divergent boundary?
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A marginal sea forms in between the continents.
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What is the newest continental divergent margin?
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the East African Rift
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What are two examples of continental divergent margins?
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the East African Rift and the Red Sea
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What are transform faults?
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when two plates slide by each other without converging or diverging
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What happens at a transform fault?
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earthquakes and some hills form
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What is the fundamental reason transform faults and fracture zones must exist?
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The earth is spherical, so the seafloor cannot spread everywhere equally.
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What is the difference between transform faults and fracture zones?
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Transform faults are where the two plates move oppositely; at fracture zones, they merely move at different rates in the same direction.
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Besides divergent margins, where can transform faults occur?
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connecting convergent and divergent margins and around subduction zones
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What happens to crust as it moves away from an oceanic ridge?
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It cools, becomes denser, and sinks in the asthenosphere. It also fills with sediment, which flattens the surface.
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What are the biggest features of oceanic ridges?
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cone-shaped volcanoes
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What do cone-shaped volcanoes of the oceanic ridge become after they move away?
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abyssal hills and seamounts
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What are flattened seamounts called?
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guyots or tablemounts
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How are guyots formed?
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Hot spots make seamounts that rise above the surface; the top of the mountain is eroded quickest and flattens out before it sinks again.
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What is the best example of the growth and decline of seamounts?
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the Hawaii Islands-Emperor Seamount chain
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What are the stages of coral reef formation?
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fringing reef, barrier reef, atoll
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Who proposed the accepted mechanism for atoll development?
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Charles Darwin
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What are continental divergent margins called?
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passive margins
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What is the first stage in the development of a passive margin?
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The boundary forms at a continental rift valley and as the continent is raised, sections slide down into valley, leaving rock debris.
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Why does the shallow sea formed at a continental rift valley have high primary productivity?
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There aren't rivers to bring sediment, so turbidity is low and light penetrates.
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What are the first things laid down in the seas of continental rift valleys?
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lots of organic matter (which becomes oil and gas) and perhaps evaporite sediments when the sea is isolated
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What happens to smooth out the boundary of a passive margin?
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The continent subsides enough for rivers to come towards it, which introduce lots of sediment.
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What are the characteristic features of passive margins?
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coastal plains, salt marshes, shallow estuaries, and thick sediment on the continental shelf
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What eventually happens to passive margins?
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They become continental convergent margins as the oceanic crust subducts, shrinking the ocean.
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How has temperature varied in the last 1000, 10k and millions of years?
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Within 1000 years, it has varied by ~.5°C. Within the last 10k years, it has varied by 2-3°C. Before this time, an ice age lasted 2-3 million years with temperatures 10°C below present levels.
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What temperatures existed during the ice age?
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Glacial maxima had temperatures 10°C below present levels, and interglacial periods had similar temperatures to today.
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Are we in an ice age right now?
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Maybe; we would be in a relatively long interglacial period if that was the case.
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Since when has temperature appeared to rise due to human causes?
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since 1920, especially in the 1990s
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What two processes link temperature and sea level directly?
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thermal expansion and forming and melting of continental ice sheets
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In the last 100 million years, when was temperature warmest and sea level highest?
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around 75M years ago
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In the last 100 million years, when was temperature coolest and sea level lowest?
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20k years ago, when sea level was 100 meters below today
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How do passive margins show evidence of sea level rise and fall?
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Where the sea level is at, erosion and deposition take place. Buried deposits of freshwater marine organisms and flattened topography are evidence of sea level fall and rise, respectively.
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How do continental shelves show evidence of a lower sea level?
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Shelf valleys exist below the surface, carved out during the last ice age, some of them now submarine canyons.
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What are the two ways sea level on a coast can change?
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eustatically and isostatically
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If isostatic and eustatic processes oppose, why don't they cancel out?
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Two reasons: First, isostasy only applies to continents that get the ice, and second, isostatic changes are slower to respond to changes than eustatic changes.
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What are the two ways ice sheets can influence topography?
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They can change sea level and create fjords.
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By how much is temperature expected to rise by 2050?
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2°C
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Which pairs of oceans are not connected?
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Indian and Arctic, and Pacific and Arctic is only through the shallow Bering Sea
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List the oceans from smallest to largest.
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Arctic, Indian, Atlantic, Pacific
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List the oceans from shallowest to deepest, on average.
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Arctic, Atlantic, Indian, Pacific
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What are the boundaries of the Pacific Ocean?
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subduction zones
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Why is the Pacific deep and the Atlantic shallow?
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The Pacific has older crust, which is cooler and denser in the mantle.
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Why is the oldest Pacific crust not much older than the oldest crust of other oceans?
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The oldest crust has been subducted.
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Why does the Pacific not get a lot of sediment?
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The subduction valleys and mountain chains limit the land area that drains into the Pacific.
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Where is the oldest coast in the Atlantic Ocean?
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the Puerto Rico-Cayman and South Sandwich trenches
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Name the four marginal seas of the Atlantic Ocean.
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the Baltic, Mediterranean, and Caribbean Seas and the Gulf of Mexico
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How does the Atlantic have so much sediment?
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It has lots of rivers running into it, like the Amazon and Congo which go directly into the equatorial Atlantic.
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When did the Indian ocean form?
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when Gondwanaland broke up
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What is the most prominent feature of the Indian Ocean?
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the Ninety East Ridge, dividing the Indian and Australian plates
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Why does the northern Indian Ocean contain a lot of sediment?
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The Himalayas, being recently formed, are easily eroded by the Indus, Ganges, and Brahmaputra.
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What is Indonesia?
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a subduction zone with island arcs and trenches
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What is the Red Sea?
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an expanding rift zone
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Where are the passive margins in the Indian Ocean?
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India and Australia
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Where did Madagascar come from?
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It broke off of India just after Pangaea itself broke up.
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What are the four types of marginal seas?
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submerged continental crust, back-arc basins, former oceans, and new oceans
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What are examples of submerged continental crust marginal seas?
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the Baltic Sea, North Sea, Baffin Bay, and Hudson Bay
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What are examples of back-arc basins and their associated island arcs?
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Java Sea (Indonesian arc), South China Sea (Phillipines), and the Bering Sea (Aleutian islants)
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What is an example of a former ocean marginal sea?
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the Mediterranean Sea
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What is an example of a new ocean marginal sea?
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the Red Sea
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