Plate Tectonics: Evidence, Boundaries, Earthquakes, and Seafloor Spreading

What evidence supports continental drift?

Seafloor spreading, fossil evidence, matching coastlines, and paleomagnetism.

Why was continental drift not accepted at first?

It lacked a mechanism explaining how continents moved.

How did mapping the seafloor support plate tectonics?

It revealed mid-ocean ridges and seafloor spreading.

How do earthquakes and volcanoes support plate tectonics?

They occur along plate boundaries, showing plates are moving.

How does seafloor spreading support plate tectonics?

New crust forms at ridges and moves outward.

How does paleomagnetism support plate tectonics?

It shows symmetrical magnetic stripes proving seafloor spreading.

How does the age of ocean floor support plate tectonics?

Youngest rock is near ridges, older rock is farther away.

What are three differences between oceanic and continental crust?

Oceanic crust is thinner, denser, and made of basalt; continental is thicker, less dense, and granitic.

What is the lithosphere?

A strong, rigid outer layer made of crust and upper mantle.

What is the asthenosphere?

A soft, plastic layer of the mantle that flows slowly.

What is the outer core made of?

Liquid iron and nickel.

What is the inner core made of?

Solid iron and nickel.

What is the relative thickness of Earth's layers?

The mantle is thickest, crust is thinnest, cores are in between.

How did knowledge of Earth's interior help plate tectonics?

It explained how plates move over the asthenosphere.

How do convection currents move plates?

Heat causes mantle material to rise and sink, moving plates.

What is slab pull?

A sinking dense plate pulls the rest of the plate into the mantle.

What is ridge push?

Gravity pushes plates away from mid-ocean ridges.

What happens at divergent boundaries?

Plates move apart and new crust forms.

What features form at divergent boundaries?

Mid-ocean ridges, rift valleys, volcanoes.

What happens at convergent boundaries?

Plates collide and one may subduct or crumple.

What features form at convergent boundaries?

Trenches, volcanoes, and mountain ranges.

Why is density important at ocean-continent boundaries?

The denser oceanic plate subducts beneath the continental plate.

What happens at continent-continent convergence?

Neither plate subducts; they form large mountains.

What happens at transform boundaries?

Plates slide past each other.

Where do transform boundaries occur?

Along faults like the San Andreas Fault.

What clues identify plate boundaries on a map?

Plate motion arrows, surface features, and crust type.

How are plate tectonics and earthquakes related?

Plate movement builds stress that causes earthquakes.

What is elastic rebound?

Rocks build stress then snap back, releasing energy.

What is the focus of an earthquake?

The point underground where the earthquake begins.

What is the epicenter of an earthquake?

The point on Earth's surface above the focus.

What are P-waves?

Fastest waves that travel through solids, liquids, and gases.

What are S-waves?

Slower waves that travel through solids only.

What are surface waves?

Slowest waves that travel along Earth's surface and cause most damage.

Can surface waves travel through materials?

No, they only travel along the surface.

What are shadow zones?

Areas where seismic waves are not detected.

How do shadow zones relate to Earth's layers?

S-waves are blocked by the liquid outer core and P-waves bend.

How do you calculate S-P lag time?

Subtract P-wave arrival time from S-wave arrival time.

How do you find distance to an epicenter?

Use S-P lag time with a travel-time graph.

What is triangulation?

Using distances from three locations to find an epicenter.

Why are seismic waves better than damage for finding epicenters?

They are more accurate and scientific.

Why is damage less reliable for locating epicenters?

It depends on buildings and population, not just distance.

How does a tsunami form?

An underwater earthquake displaces water, creating waves.

What happened in the 2011 Japan tsunami?

Subduction caused the seafloor to rise, displacing water and forming a tsunami.