Question

List the three major layers of Earth. Which is/are composed of rock, which is/are metallic? Which is the largest; which is the thinnest?

Short answer

The Earth's layers are the crust (rock), mantle (rock), and core (metallic). The mantle is the largest; the crust is the thinnest.

Step-by-step solution

Identify the Major Layers

The Earth is composed of three major layers: the crust, the mantle, and the core.

Determine Composition of Each Layer

The crust is primarily composed of rock. The mantle is also primarily made up of rock, characterized by silicate minerals. The core is metallic, primarily composed of iron and nickel.

Determine Size and Thickness of Layers

The mantle is the largest layer, accounting for about 84% of Earth's volume. The crust is the thinnest layer, comprising only about 1% of Earth's total volume.

Key concepts

Crust

The Earth's crust is its outermost layer, where we live and build our homes. It's remarkably thin compared to the other layers, accounting for less than 1% of Earth's total volume. Despite its thinness, the crust is solid and composed primarily of rock.

There are two types of crust:

• **Continental Crust:** Thicker but less dense, primarily made up of granite.
• **Oceanic Crust:** Thinner and denser, consisting mostly of basalt.

The varied composition of these crusts contributes to tectonic activity and the constantly-changing landscape on Earth. Interesting fact: when we talk about tectonic plates moving, we're actually referring to pieces of the crust moving slowly over the more molten layers beneath.

Mantle

Beneath the crust lies the mantle, which is the largest of Earth's layers. It makes up about 84% of the planet's volume, effectively acting as the thick blanket surrounding the core. The mantle is primarily composed of silicate rocks rich in oxygen, silicon, and magnesium, giving it a rocky and yet partially molten consistency.

The mantle isn't entirely solid; it behaves like a thick fluid over geological time scales:

• **Upper Mantle:** Partially molten, allowing the lithosphere to float.
• **Lower Mantle:** More rigid due to higher pressure, but still able to flow very slowly.

The movement within the mantle is responsible for the tectonic activity that shapes our continents and oceans. It is the heat from the mantle that creates convection currents, driving the movement of tectonic plates atop the more pliable asthenosphere.

Core

Deeper still, at the center of the Earth, lies the core. This metallic region is mainly composed of iron and nickel, which gives the core its dense and heavy characteristics. The core itself is divided into two distinct parts:

• **Outer Core:** A hot liquid layer responsible for generating Earth's magnetic field. This layer moves more freely than the layers above it, swirling around the inner core.
• **Inner Core:** Although extremely hot, the immense pressure keeps it solid. It's like having an iron-nickel ball at the Earth's center.

The core makes up about 15% of Earth's volume. The differences in the movement of the outer core compared to the solid inner core contribute to the dynamo effect, a fundamental process that generates Earth's magnetosphere. This magnetic field extends far beyond the planet's surface and is crucial for protecting life on Earth from solar winds.