What does the theory of Plate Tectonics help explain about Earth?

• How plants grow and make food.

• The structure and behavior of our planet.

• Why the sky is blue.

• How stars are formed.

What happens to Earth's outer shell, the crust, over time?

• It stays exactly the same.

• It slowly melts away into space.

• It rises from the mantle and falls back in, recycling material.

• It gets covered by new layers of ice.

What is the theory of Plate Tectonics considered in Earth science?

• A small, unimportant idea.

• A theory about how animals change over time.

• The grand unifying theory.

• A theory about how planets are born.

What are the large, rocky pieces that make up Earth's outer layer called?

• Oceanic plates.

• Lithospheric plates.

• Continental plates.

• Mantle plates.

Who first suggested that all the continents were once joined together in a single supercontinent?

• Marie Tharp.

• Harry Hess.

• Alfred Wegener.

• Robert Dietz.

Why was Alfred Wegener's idea of moving continents not fully accepted by other scientists at first?

• He did not have enough evidence to support his idea.

• He was not a geologist and couldn't explain how continents moved.

• His maps were incorrect.

• Scientists believed the Earth was flat.

What important feature did Bruce Heezen and Marie Tharp discover on the Atlantic Ocean floor?

• A giant volcano.

• The deepest trench in the world.

• A vast mid-oceanic mountain range.

• A large, flat plain.

According to Harry Hess's idea of seafloor spreading, what happens at mid-oceanic ridges?

• Old seafloor is pulled down into the Earth.

• Magma spills out, creating new seafloor and pushing old seafloor away.

• Continents crash into each other.

• Mountains are formed on land.

What is subduction?

• When two plates slide past each other.

• When one plate is pushed under another plate.

• When two plates pull apart from each other.

• When a plate breaks into smaller pieces.

Why does the oceanic plate dive beneath the continental plate during subduction?

• The oceanic crust is denser than the continental crust.

• The continental crust is denser than the oceanic crust.

• Both oceanic and continental crusts have the same density.

• Density does not affect how plates move.