Unit 4.2: Earth's shifting crust Flashcards
what is the continental drift theory?
First proposed by Alfred Wegner in 1915. Says continents move slowly over earth’s surface. The theory that the crust is composed of plates that move.
In terms of the continental drift theory, what is Pangaea, Laurasia, and gondawa?
Pangaea: the landmass that was at one time composed of all of the continents.
Laurasia: North America, Greenland, Eurasia
Gondawa: South America, Africa, Australia, India, Antartica.
What is some evidence for the continental drift theory?
- continents seem to be able to fit together like a puzzle.
- Rock types and fossils that are similar are found on different continents. This implies that they were once close together in proximity.
- the location and features like mid-oceanic ridges and trenches prove that there are plates and they move.
what are the two different types of tectonic plates?
- primary plates: larger plates
- secondary plates: smaller plates
how much do tectonics plates move per year?
2-10cm
what 3 ways do tectonic plates move relatively to each other?
1: ridge push: magma rises along a mid-ocean ridge, lifting the oceanic lithosphere and forcing it apart.
2: mantle drag: the lateral flow beneath plates between the asthenosphere and the lithosphere.
3: slab pull: weight of the subducting portion of the plate accelerates plate movement by pulling the plate deeper into the mantle.
what is a divergent plate boundary?
when plates move apart (away) from each other.
what are some features of a divergent plate boundary?
- mid-oceanic ridge: when the boundary is underwater and magma pushes up and creates a mid oceanic ridge.
- rift and Rift Valley: when it happens on the continent, volcanic activity develops at the bottom of the rift/valley and forms new crustal material.
what is a convergent plate boundary?
when two plates are pushed together.
what three situations happen can happen on convergent boundaries?
- continental and oceanic plates: the oceanic plate will go under the continental plate cause it is more dense. this will form volcanic arcs/mountain ranges and deep sea trenches.
- two oceanic plates: one will go under the other, form volcanic island arcs and deep sea trenches.
- two continental plates: one will not go completely under the other and no magma goes to the surface. one plate will be forced upwards and form a mountain range.
what is accreted terrane?
form overtime where there is a convergent boundary. It is a mass of crust that is moved due to one plate pushing it into the other and fusing it there.
what is a transform boundary?
2 plates slide laterally past one another. they can “catch” on each other and can cause an earthquake.
