What is a transform boundary?
A boundary where plates slip past each other
Why does subduction occur?
More dense oceanic crust slips underneath less dense continental crust
What is a fossil?
Any trace of an ancient organism that has been preserved in rock
What is a convergent boundary?
A boundary where plates come together
What is a divergent boundary?
A boundary where plates move apart
How can fossils be used as evidence of continental drift?
Fossils of the same species have been found on different continents
What are mid-ocean ridges?
Long chains of mountains that rise up from the ocean floor
What is a rift valley?
A land formation that occurs when two plates diverge on land
What does the theory of plate tectonics state?
Earth's plates are in slow, constant motion driven by convection currents in the mantle
Why are the oldest parts of the ocean floor only about 200 million years old?
Very old parts of the ocean floor undergo subduction at deep-ocean trenches
Where does subduction occur?
Deep-ocean trenches
What is a deep-ocean trench?
A deep underwater canyon where subduction occurs
What did Wegener's hypothesis state?
All continents were once joined together in a single landmass that has since drifted apart
What is a fault?
A break in Earth's crust where rocks have slipped past each other
How is pillow lava evidence of sea-floor spreading?
It shows that new material is being added at mid-ocean ridges
What happens during sea-floor spreading?
New crust is added to the ocean floor, and older strips of rock move outward from either side of the ridge.
What is subduction?
The process by which part of the ocean floor sinks back into the mantle at a deep-ocean trench
What is continental drift?
The idea that the continents slowly move over Earth's surface
What is pillow lava?
Pillow-shaped rock found at mid-ocean ridges formed when molten material hardens quickly after erupting underwater
What is Pangaea?
The supercontinent
What is a plate?
A piece of Earth's crust