Earth’s Interior (pages 124–131)

Exploring Inside Earth (pages 125–126)

Key Concept: Geologists have used two main types of evidence to learn about Earth’s interior: direct evidence from rock samples and indirect evidence from seismic waves.

• Scientists cannot travel inside Earth to explore it. So scientists must learn about Earth’s interior, or inside, in other ways.

• Scientists use drills to get rock samples from inside Earth.

The rock samples help scientists learn what conditions were like inside Earth when the rocks formed.

• Scientists study how seismic waves travel through Earth.

Seismic (SYZ mik) waves are waves made by earthquakes.

Seismic waves show that Earth is made up of layers like an onion.

1. Circle the letter of a way that scientists can learn about Earth’s interior.

a. travel inside Earth and explore it directlyb. study rock samples from inside Earthc. peel away Earth’s layers

like an onion

2. Is the following sentence true or false?

Earth is made up of layers.

TRUE

A Journey to the Center of Earth (page 127)

Key Concept: The three main layers of Earth are the crust, the mantle, and the core.

These layers vary greatly in size, composition, temperature, and pressure.

Layers of the Earth Video

• Earth has three main layers.

1. The crust is the outside layer. (1% or earth’s mass)

2. The mantle is the middle layer. (68% of earth’s mass)

3. The core is the inside layer.(31% of earth’s mass)

• Temperature increases from the crust to the core.

It is very hot inside Earth.

One reason it is so hot is that some substances inside Earth give off energy.

Earth Guide

• Temperature increases from the crust to the core.

• Pressure also increases from the crust to the core. Pressure is caused by a force pressing on an area.

There is great pressure inside Earth because of all the rock pressing down from above.

CORE

MANTLE