Earth’s Changing Surface
What Earth process can cause sudden cracks in the ground during an earthquake?
Faulting
What does the Law of Superposition say about rock layers?
Oldest on bottom, youngest on top, unless disturbed
Which boundary type causes mountains to form when plates collide?
Convergent (continental-continental)
Where is the youngest rock on the ocean floor found?
Closest to the mid-ocean ridge
Who first proposed the idea of continental drift?
Alfred Wegener
Which two forces shape mountains over time?
Uplift and erosion
A fault cuts across three rock layers. Which is older, the fault or the layers?
The layers (cross-cutting rule)
At which boundary type does new crust form?
Divergent, at mid-ocean ridges
What evidence shows that ocean rocks near ridges are younger than those farther away?
Rock samples show that the age increases with distance from the ridge.
What was the name of the supercontinent that existed 335–175 million years ago?
Pangaea
Give an example of a fast vs. slow Earth surface change.
Fast = earthquake/landslide; Slow = mountain building/erosion
How do fossils help scientists determine the relative ages of rocks?
Fossils indicate time periods and correlate layers across locations
What type of boundary is the San Andreas Fault?
Transform
What do symmetrical magnetic stripes on either side of ridges prove?
New crust is added equally on both sides → sea-floor spreading
What fossil evidence supports continental drift?
Identical fossils on continents now far apart
What evidence at Ridgecrest, California showed plates were moving?
Surface cracks and displacement of land features
Why might rock layers be tilted or folded?
Plate movement/tectonic forces
What happens when oceanic crust collides with continental crust?
Oceanic crust subducts, forms volcanoes and trenches
Why are rocks older farther from the ridge?
They formed earlier and were pushed outward as new crust formed
Why didn’t scientists accept Wegener’s theory at first?
He couldn’t explain the mechanism for movement
Why is it important to study patterns of earthquakes and volcanoes worldwide?
They reveal plate boundary locations and movements
A younger layer lies directly on much older rock. What event likely happened?
Erosion before the younger layer was deposited
Explain how rift valleys form.
Continental crust pulls apart at divergent boundaries, creating valleys
What role do trenches play in the rock cycle of ocean crust?
Old crust is subducted back into the mantle
How did sea-floor spreading provide the missing mechanism for Wegener’s theory?
It showed how continents are carried by moving plates as new crust forms and old crust subducts