Earth Space Science Chapter 9
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sunday 10.28.26
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What is continental drift?
The idea that continents were once joined and slowly moved apart.
Who proposed continental drift?
Alfred Wegener.
What was Wegener's supercontinent called?
Pangaea.
What does Pangaea mean?
All land.
What evidence supported continental drift?
Matching coastlines, fossils, rocks, mountains, and ancient climates.
How did continents' shapes support continental drift?
South America and Africa fit together like puzzle pieces.
How did fossils support continental drift?
The same fossils were found on continents now separated by oceans.
Why was Mesosaurus important?
Its fossils were found in South America and Africa, but it couldn't swim across the ocean.
How did ancient climates support continental drift?
Glacial evidence was found in places that are warm today.
What did matching rocks and mountains prove?
Continents were once connected.
Why was Wegener's hypothesis rejected?
He couldn't explain what force moved the continents.
What is sea-floor spreading?
New ocean floor forms at ridges and moves outward.
Where is new ocean floor created?
At mid-ocean ridges.
What is a mid-ocean ridge?
A long underwater mountain chain where new crust forms.
What is a rift valley?
A deep valley where plates pull apart.
What is a deep-ocean trench?
A long, deep valley where one plate sinks beneath another.
What is a subduction zone?
A place where one plate sinks beneath another into the mantle.
What happens to old oceanic lithosphere?
It sinks into the mantle at subduction zones.
What is paleomagnetism?
The record of Earth's past magnetic field stored in rocks.
How does paleomagnetism support sea-floor spreading?
Matching magnetic stripes on both sides of ridges show the floor spreads apart.
What is normal polarity?
Rock magnetism matches Earth's current magnetic field.
What is reverse polarity?
Rock magnetism is opposite Earth's current magnetic field.
Where is the youngest ocean floor?
At mid-ocean ridges.
Where is the oldest ocean floor?
Farthest from the ridge, usually near continental margins.
What happens to ocean-floor age farther from a ridge?
It gets older.
What is plate tectonics?
Earth's lithosphere is broken into moving plates.
What layer contains Earth's tectonic plates?
The lithosphere.
What is the lithosphere?
The crust and rigid uppermost mantle.
What is the asthenosphere?
A softer layer of the upper mantle beneath the lithosphere.
How fast do tectonic plates move?
About 5 centimeters per year on average.
What are the three plate boundaries?
Divergent, convergent, and transform.
What happens at a divergent boundary?
Plates move apart and new crust can form.
What happens at a convergent boundary?
Plates move toward each other.
What happens at a transform boundary?
Plates slide past each other.
Where is lithosphere created?
At divergent boundaries.
Where is lithosphere destroyed?
At subduction zones along convergent boundaries.
What happens at oceanic-continental convergence?
The oceanic plate sinks beneath the continental plate.
What happens at oceanic-oceanic convergence?
One oceanic plate sinks beneath the other, forming a trench and volcanic island arc.
What happens at continental-continental convergence?
Continents collide and form mountains.
How do volcanic island arcs form?
One oceanic plate sinks beneath another, causing magma to rise and form islands.
How do continental volcanoes form?
An oceanic plate sinks beneath a continent, causing magma to rise.
What happens at transform faults?
Plates slide past each other.
Where are most transform faults found?
On the ocean floor, connecting sections of mid-ocean ridges.
What drives plate motion?
Heat from Earth's interior and forces linked to mantle convection.
What is mantle convection?
Hot, less dense material rises while cooler, denser material sinks.
What is ridge-push?
Gravity causes oceanic lithosphere to slide away from an elevated ridge.
What is slab-pull?
A sinking oceanic plate pulls the rest of the plate behind it.
What is the difference between ridge-push and slab-pull?
Ridge-push moves plates away from ridges; slab-pull pulls plates into the mantle.
What are examples of oceanic-continental convergence? (continental volcanoes)
Andes and Cascade Mountains.
What are examples of volcanic island arcs?
Java and Sumatra