Chapter 4 - Plate Tectonics

Inside the Earth

Restless Continents

The Theory of Plate Tectonics

Deforming the Earth’s Crust

Inside the Earth

Earth’s Layers

• Inner Core

• Outer Core

• Mantle

• Crust

The Earth’s Crust

• Outermost layer of the Earth• 5 – 100km thick• Less than 1% of the mass of the Earth, yet

humans have not ever drilled all the way through it.

• Two types:– Continental Crust – Oceanic Crust

Oceanic Crust - Thinner and more dense

Continental Crust - Thicker and less dense

Mantle

The Earth’s Mantle

• Between the crust and the core

• 2900 km thick• 67% of the Earth’s mass• Three parts

– Lithosphere (half in the crust)

– Asthenosphere– Mesosphere

Layers of the Mantle

Layers of the Mantle

-- Lithosphere is the rigid layer of the Earth that includes the crust and the upper part of the mantle.

Layers of the Mantle

-- Asthenosphere is the soft plastic-like layer of the mantle on which the pieces of the lithosphere float.

Layers of the Mantle

-- Mesosphere is the strong lower part of the mantle.

The Core

• Innermost layer of the Earth

• 3430 km radius• 33% of Earth’s mass• Made mostly of iron• Two layers

– Outer core– Inner core

Layers of the Core

-- Outer Core is liquid

Layers of the Core

-- Inner Core is solid

Tectonic Plates

Pieces of the lithosphere that move around on top of the asthenosphere

These plates are made up of both continental crust and oceanic crust.

Mapping the Earth’s Interior Scientists have figured out what the Earth’s

interior looks like by studying how earthquake (seismic) waves travel through the Earth.

Seismic waves travel at different speeds when they travel through materials with different densities.

Scientists measure how long it takes the waves to travel through the Earth to different

locations, then make calculations to figure out

what the inside of the Earth is composed of.

Seismologists can then use the distances and travel times to calculate the density and thickness of each layer of the

Earth.

USGS Earthquake Hazards Program: Animation of Seismic Waves: CENTRAL ALASKA

Seismograph Scientists us a device called a seismograph

to measure arrival time and magnitude of seismic waves around the Earth.

Seismograph