Plate Tectonics: Earth's Crust, Movement, and Evidence pt2

What is Plate Tectonics?

The study of the formation and movement of large rigid pieces called plates that cover the Earth's crust.

How many major tectonic plates are there?

There are 12 major plates along with a number of minor plates.

What is the thickness of the lithosphere?

The lithosphere is about 100 km thick.

What types of rocks make up the oceanic and continental crust?

The oceanic crust is made of basalt, while the continental crust is made of granite.

What is the asthenosphere?

The plastic mantle beneath the lithosphere, composed of partially melted rock that flows slowly.

What is slab pull?

The process where older crust dives back into the Earth, helping to pull apart the slab of crust at mid-ocean ridges.

What evidence supports the theory of continental drift?

Similar coastlines of Africa and South America, fossil evidence like the Mesosaurus, and distinctive rock formations.

What climate evidence supports continental drift?

Tropical plant remains found in Antarctica and coal fields in North America matching those in Europe and Asia.

Where are earthquakes and volcanoes predominantly located?

In definite belts around the world, particularly at tectonic plate boundaries.

What is the 'Ring of Fire'?

The largest and most active belt of earthquakes and volcanoes surrounding the Pacific Ocean.

What is paleomagnetism?

The study of the Earth's ancient magnetic field as recorded in rocks, sediments, and archaeological materials.

What happens to the age of rocks as you move away from a mid-ocean ridge?

The rocks get older as you move away from the ridge.

What are rift valleys?

Long, deep valleys along mid-ocean ridges where two lithospheric plates are moving apart.

What is a transform boundary?

A boundary where lithospheric plates slide past each other in a side-by-side motion.

What is an example of a transform boundary?

The San Andreas Fault.

What occurs at spreading centers or mid-ocean ridges?

New rock is formed while older rock is pushed aside as plates move apart.

What is the relationship between temperature and distance from a mid-ocean ridge?

As you move away from the mid-ocean ridge, the temperature of the crust decreases.

What is the composition of the lithosphere?

It is a solid layer composed of the crust (oceanic or continental) and the rigid upper mantle.

What geological feature is formed by movements along fracture zones?

Earthquakes occur due to movements along fracture zones.

What are transform boundaries?

Boundaries where lithospheric plates slide past each other in a side-by-side motion.

Give an example of a transform boundary.

The San Andreas Fault.

What occurs at converging boundaries?

Two lithospheric plates move towards each other.

What happens during a continental-continental collision?

Plates carrying continents collide and weld together to form a larger continent.

What geological feature resulted from the collision of India with SE Asia?

The Himalayan Mountains.

What is formed when two oceanic plates collide?

One plate subducts underneath the other, forming a deep ocean trench and volcanic islands.

What is the overriding plate in oceanic-oceanic collisions?

The younger, less dense plate that remains above the subducting plate.

What is a Benioff zone?

A region where earthquakes originate deeper in the Earth's interior, typically found at subduction boundaries.

What are hotspots?

Areas of volcanic activity resulting from plumes of hot solid material rising from deep within the Earth's mantle.

What is an example of a hotspot?

The Hawaiian Islands.

How are the Hawaiian Islands formed?

They are formed by volcanic eruptions over a hotspot as the Pacific Plate moves over it.

What causes earthquakes?

Stress between tectonic plates that releases energy when overcome.

What is the Elastic Rebound theory?

The theory that explains how plates snap back to their original shapes after being deformed.

What is the focus of an earthquake?

The point at which the movement occurs on a fault line.

What is the epicenter of an earthquake?

The spot on the Earth's surface directly above the focus.

What are primary waves (P-waves)?

Waves that compress and stretch rock material, traveling through solids, liquids, and gases.

How fast do P-waves travel?

4-5 km/sec.

What are secondary waves (S-waves)?

Waves that cause particles to move at right angles to the direction of wave travel and can only travel through solids.

How fast do S-waves travel?

1-3 km/sec.

What happens to P-waves at a depth of 2900 km?

They slow down greatly as they transition to the outer core.

Why can't S-waves travel through the outer core?

Because they cannot travel through liquids.

What is inferred about the Earth's outer and inner core?

Both are believed to be composed of iron and nickel based on meteorite studies.

At what depth do P-waves increase in velocity again?

At 5150 km depth, where the solid inner core begins.