Lesson 2: Earth's Composition

Key Idea

Earth's surface features are diverse, ranging from towering mountains to deep oceans. However, beneath all these features—including the sediment on the ocean floor—lies a continuous layer of hard, solid rock.

This layer is known as the crust. It is not interrupted by the water of the oceans. It acts as a global shell, meaning that if you drill deep enough anywhere on the planet, you will eventually hit this solid rock foundation.

Key Idea

Since humans cannot physically travel deep underground, scientists use scientific drilling to gather direct evidence. Powerful machines bore into the Earth on land and underwater to extract core samples.

These cylindrical rock samples provide a snapshot of the materials below. By analyzing cores from around the world, geologists have confirmed that the outer layer is consistently made of solid rock, validating their models of Earth's composition.