Earth's Layers — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. When two plates collide, one plate may slide beneath the other in a process called subduction.
Subduction happens when a denser oceanic plate dives beneath a lighter plate, sinking into the hot mantle where it eventually melts.
2. A transform boundary forms where two plates slide past each other in opposite directions.
Transform boundaries involve plates grinding sideways past each other rather than colliding or separating, which builds up stress that releases as earthquakes.
3. New ocean floor is created at divergent boundaries where plates pull apart and magma rises.
Divergent means "moving apart," and as plates separate at these boundaries, magma wells up from the mantle to form fresh oceanic crust.
4. The Himalaya Mountains formed when two continental plates pushed into each other over millions of years.
The Himalayas formed when the Indian and Eurasian continental plates collided, and because neither plate could subduct, the crust buckled upward into the tallest mountains on Earth.
5. Deep ocean trenches form where an oceanic plate dives beneath another plate.
Ocean trenches are the deepest spots on Earth's surface, carved out where a sinking oceanic plate bends downward into the mantle during subduction.
6. The San Andreas Fault in California is an example of a transform plate boundary.
The San Andreas Fault is a transform boundary where the Pacific and North American plates slide past each other, causing frequent earthquakes in California.
7. The Mid-Atlantic Ridge is an underwater mountain chain formed by plates pulling apart.
The Mid-Atlantic Ridge is an enormous underwater mountain chain running down the Atlantic Ocean floor, built by magma rising where the plates on either side slowly pull apart.
8. A convergent boundary is a place where two tectonic plates move toward each other.
"Convergent" means coming together, so at a convergent boundary two plates push toward each other, which can create mountains, trenches, or volcanoes.
9. Island arcs form when volcanoes erupt along a subduction zone in the ocean.
Island arcs are curved chains of volcanic islands, like Japan, that form when magma from a subducting plate rises through the ocean floor and builds up over time.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Convergent boundary
→ Plates push together and may build mountains or trenches
Plates slide sideways past each other, causing earthquakes
Divergent boundary
→ Plates pull apart and new crust forms from rising magma
One plate sinks beneath another into the hot mantle
Transform boundary
→ Plates slide sideways past each other, causing earthquakes
Plates pull apart and new crust forms from rising magma
Subduction zone
→ One plate sinks beneath another into the hot mantle
Plates push together and may build mountains or trenches
Correct matches: Convergent boundary → Plates push together and may build mountains or trenches; Divergent boundary → Plates pull apart and new crust forms from rising magma; Transform boundary → Plates slide sideways past each other, causing earthquakes; Subduction zone → One plate sinks beneath another into the hot mantle.