04 Plate Tectonics Free Online FlashCards

What makes up the lithosphere?

The lithosphere is Earth's rigid outer layer, made of the crust and the rigid uppermost mantle.

What is the asthenosphere?

The asthenosphere is the warmer, ductile mantle beneath the lithosphere. It is mostly solid rock that can deform and flow slowly, not a global ocean of magma.

What did Wegener propose about the continents?

Alfred Wegener proposed that continents had once been joined in the supercontinent Pangaea. Continental fit, matching fossils and rocks, and ancient climate clues supported the idea.

Why was Wegener's proposal not initially accepted?

Wegener could not explain a convincing physical mechanism for moving continents, so his proposal was not initially accepted.

How does seafloor spreading create new oceanic crust?

At mid-ocean ridges, magma rises and cools to form new oceanic crust. The new crust moves older seafloor away from the ridge.

What happens during subduction?

Subduction occurs where one plate bends and sinks beneath another. Oceanic crust is recycled into the mantle at many trenches.

How do continents move with respect to the ocean floor?

Continents move because they are embedded in moving plates; they do not plow through the ocean floor.

How do magnetic stripes support seafloor spreading?

Iron-bearing minerals in cooling lava record Earth's magnetic-field direction. Reversals leave alternating bands that match on opposite sides of ridges as seafloor moves outward.

How does oceanic crust age vary with distance from a ridge?

Oceanic crust is youngest near spreading ridges and generally gets older farther away, consistent with new crust forming at ridges and being recycled at subduction zones.

What do global patterns of earthquakes and volcanoes reveal?

Earthquakes and volcanoes outline many plate boundaries. Earthquakes can extend deep beneath subduction zones, while spreading ridges and transform faults have shallow earthquakes.

How can scientists measure plate motion directly today?

Satellite-based GPS measurements track plate motion directly today, confirming that plates move slowly, often at rates comparable to fingernail growth.

What is slab pull?

Slab pull occurs when old, cold, dense oceanic lithosphere sinks at a subduction zone and pulls the rest of its plate behind it. It is often considered a major driver of plate motion.