plate motion

plate motion

• cause mountains to rise where plates push together or converge

• cause continents to fracture and oceans to form where the plates pull apart or diverge

continent accretion theory

states that the continents have always been stationary, with the gradual addition of new material around the nucleus

james dwight dana

who proposed the continent accretion theory?

continental assimilation hypothesis

states that the ocean accumulated the denser elements then subsided to form basins

expanding earth hypothesis

states that the present continents split apart with the expansion of earth and that the continents combined could cover half of the current earth’s surface area

continental drift theory

states that the continents once existed as a single landmass

pangaea

the single landmass in the continental drift theory is called

panthalassa

pangaea was covered by one big ocean called

tethys

a sea called _______ divided pangaea into two huge landmasses

• laurentia | laurasia (north)

• gondwanaland (south)

the two landmass that was divided by a sea called tethys

200mya (mesozoic era, triassic period, late triassic epoch)

when did the drift started based on the continental drift theory

• the fit of the continental shorelines

• distribution of glacial sediments

• paleoclimate

• distribution of fossils

• distribution of rocks

evidences of the continental drift theory

alfred wegener

who proposed the continental drift theory

paleoclimate

• one piece of evidence wegener provided was paleoclimatic indicators that linked south america and africa

• noted that glacial, tropical rain forests, and dessert deposits were aligned when the continents were placed together

harry hess (1960)

who studied wegener’s continental drift theory

seafloor spreading

• is a geologic process in which tectonic plates split apart from each other as a result of mantle convection

• it occurs at divergent plate boundaries

• formation of ocean ridges (large mountain ranged) arising from the ocean floor

• the process that continually adds new material to the ocean floor while pushing older rocks away from the ridge

• new ocean floor forms along cracks in the ocean crust as molten material erupts from the mantle spreading out and pushing older rocks to the sides of the crack

conveyor belt

ocean floor moves like a ________ ____ carrying continents with it

sonar

• a device that bounces sound waves off underwater objects and then records the echoes of these sound waves

• the time it takes for the echo to arrive indicates the distance of the object

mid-ocean ridge

the longest chain of mountains in the world (divergent plate boundaries)

subduction

• process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle

• allows part of the ocean floor to sink back into the mantle

• african plate

• antarctic plate

• eurasian plate

• australian plate

• north american plate

• pacific plate

• south american plate

seven major plates

• arabian plate

• caribbean plate

• cocos plate

• juan de fuca plate

• nacza plate

• philippine plate

• scotia plate

seven largest minor plates

plate tectonics

• is the theory that earth’s outer shell is divided into several plates that glide over the mantle

• the plates act like a hard rigid shell compared to mantle

lithosphere

• the strong outer layer of a plate which is 100km (60mi) thick

• includes crust and other part of the mantle

asthenosphere

• is a malleable part of a plate allowing the lithosphere to move around

• located below the lithosphere

divergent boundary

• occurs when two tectonic plates move away from each other

• frequent earthquakes strike along the rift

• beneath the rift, magma rises from the mantle, it hardens into solid rock and forms new crust

• oceanic crust made of basalt is created

continental-continental boundaries

are when two continental plates converge and neither of them is subducted below the other because the continental rocks are relatively light and resist downward motion

oceanic-continental boundaries

are when an oceanic and a continental plate converge and the denser oceanic plate is subducted below the continental plate

oceanic-oceanic boundaries

• are when two oceanic plates converge

• one plate is usually subducted under the other and in the process a deep oceanic trench is formed and can also result in the formation of undersea volcanoes

convergent boundary

this is where two plates converge

transform boundary

• occurs when two plates sliding are past each other

• natural or human made structures that cross a ___________ ____________ are offset-split and carried in opposite directions