Question

The zone from \(\sim 20-2,900 \mathrm{~km}\) represents the Earth's: a. crust b. mantle c. inner core d. outer core

Short answer

The zone from 20-2,900 km represents the Earth's mantle.

Step-by-step solution

Understanding the Earth’s Layers

The Earth is composed of different layers: the crust, mantle, outer core, and inner core. Each layer varies in depth and has distinct characteristics.

Identifying the Depths of Earth’s Layers

The Earth’s crust extends from the surface to about 35 kilometers deep on average, though it varies in thickness. The mantle lies beneath the crust and extends from 35 to about 2,900 kilometers deep. The outer core lies below the mantle and extends from 2,900 to about 5,150 kilometers deep. Finally, the inner core extends from 5,150 kilometers to the center of the Earth, approximately 6,371 kilometers from the surface.

Analyzing the Depth Range in the Question

The question specifies the depth range from 20 kilometers to 2,900 kilometers. This range begins within the crust (starting at around 20 kilometers) and runs through to the end of the mantle, which reaches 2,900 kilometers deep.

Conclusion

Given the depth range specified (20-2,900 kilometers), we determine that this range fully encompasses the Earth's mantle. Therefore, the zone described in the question represents the mantle.

Key concepts

Earth's Crust

The Earth's crust is the outermost layer of our planet. It is the surface that we walk on and is where we find landforms like mountains, valleys, and oceans. Although it is the thinnest of Earth's layers, it plays a crucial role in supporting life. Beneath it lies a wealth of resources, including minerals that are essential for various industries.

The crust is composed of two types: the oceanic crust and the continental crust.

• Oceanic Crust: This part of the crust is thinner, averaging about 5-10 kilometers in thickness. It is primarily composed of dense basaltic rocks.
• Continental Crust: Thicker than oceanic crust, it varies in thickness from around 30 to 70 kilometers. It is made up mostly of less dense granite rocks.

Understanding the structure and composition of the Earth's crust helps in studying geological processes. For example, the movement of tectonic plates, which float on the underlying mantle, leads to earthquakes and the formation of mountains.

Earth's Mantle

Lying just beneath the Earth's crust is the immense mantle, which is the largest layer of the Earth, extending from about 35 kilometers to 2,900 kilometers below the surface. The mantle is primarily composed of silicate rocks rich in iron and magnesium.

The mantle is divided into several parts based on geological features and mechanisms:

• Upper Mantle: This portion extends to about 660 kilometers deep. It includes the lithosphere and the highly viscous asthenosphere, where rock is semi-molten and capable of flowing slowly. This flow is critical for plate tectonics.
• Transition Zone: Found between 410 and 660 kilometers, this zone separates the upper and lower mantle. It contains minerals that change structure at varying depths.
• Lower Mantle: Below the transition zone, extending down to the outer core, this portion has more rigid materials due to high pressures.

The mantle influences tectonic activity and is pivotal in driving the motion of tectonic plates due to convection currents created by the heat from the Earth's core. This results in phenomena like continental drift and volcanic eruptions.

Earth's Core

At the heart of our planet lies the Earth's core, split into two distinct parts: the outer core and the inner core. Both play vital roles in generating the Earth's magnetic field.

The core is composed primarily of iron and nickel, with the core's temperatures soaring to thousands of degrees Celsius.

• Outer Core: This liquid layer extends from about 2,900 kilometers to 5,150 kilometers beneath the surface. The fluid movement in the outer core creates the Earth's magnetic field.
• Inner Core: In contrast, this innermost layer, ranging from 5,150 kilometers to the Earth's center at 6,371 kilometers, is solid due to immense pressure, despite its hot temperatures.

The study of the Earth's core is crucial, as it provides insight into the dynamics of magnetic fields and the history of our planet. The energy and heat from the core impact not only the planet's geology but also its magnetic properties, which protect the Earth from solar and cosmic radiation.