Question

The zone from \(\sim 2,900-5,100 \mathrm{~km}\) represents the Earth's: a. crust b. mantle c. inner core d. outer core

Short answer

The Earth's outer core.

Step-by-step solution

Understanding Earth’s Layers

The Earth is composed of four primary layers: the crust, mantle, outer core, and inner core. These layers differ in composition, physical properties, and depth. The crust is the outermost layer. Below it is the much thicker mantle, which stretches until about 2,900 km. The outer core then extends from approximately 2,900 km to 5,100 km, followed by the inner core that stretches beyond 5,100 km.

Identifying the Depth Range

The question specifies a depth range of \( \sim 2,900-5,100 \, \text{km} \). This range aligns with the region known as the outer core of the Earth. The outer core is a liquid layer, primarily made up of iron and nickel, positioned between the solid mantle and the solid inner core.

Matching the Depth to Earth's Layers

Now, we match the provided depth range to the corresponding Earth layer. Since the outer core extends from about 2,900 km to 5,100 km, the given depth range fits perfectly within the outer core's boundaries.

Key concepts

Earth's Crust

The Earth's crust is the outermost layer of our planet, much like the shell of an egg. It's the layer where we live, build our homes, and grow our food. The crust is composed mainly of solid rocks and minerals, and it's divided into two types based on its composition and thickness:

• **Continental Crust:** This is the part of the crust that forms the landmasses. It's thicker, averaging about 35 to 70 kilometers, and contains a variety of rock types such as granite.
• **Oceanic Crust:** Found under the oceans, this crust is thinner, about 5 to 10 kilometers thick, and mainly consists of basalt.

The crust is split into large pieces called tectonic plates, which move slowly over the surface of the Earth. This movement is responsible for major geological events such as earthquakes and volcanic eruptions.
The temperature of the crust varies, but it increases as you go deeper, transitioning smoothly into the layer beneath—the mantle.

Earth's Mantle

Beneath the crust lies the mantle, which makes up about 84% of Earth's volume. The mantle extends from the base of the crust to a depth of about 2,900 kilometers. This layer is composed mostly of silicate minerals rich in iron and magnesium. The mantle is solid yet behaves like a very slow-moving liquid over millions of years, allowing for the convection currents that drive plate tectonics. This convection is a result of the mantle's heat, which originates from the core and the decay of radioactive elements.
The upper part of the mantle, which interacts directly with the crust, is called the lithosphere and is more rigid. Beneath this is the asthenosphere, a softer, more ductile region where the rocks are closer to melting.
The mantle plays a crucial role in the Earth's internal processes, affecting everything from the formation of mountains to the recycling of crustal materials.

Earth's Outer Core

The outer core is a fascinating part of Earth's structure, located between 2,900 km and 5,100 km beneath the surface. Unlike the solid crust and mantle, the outer core is in a liquid state. This layer is primarily made up of molten iron and nickel.
As a liquid layer, the outer core is crucial for generating Earth's magnetic field. The movement of the molten metal creates electric currents, which in turn produce magnetic fields. These fields combine to form the Earth's geomagnetic field, which shields us from solar radiation and helps guide navigation systems.
The outer core's dynamic nature also impacts geological phenomena such as plate tectonics and volcanic activity. It's an active and vital part of Earth's geodynamics, playing a central role in the planet's magnetic and thermal balance.