Compositional and mechanical layers of the earth | Cosmology & Astronomy | Khan Academy

Summary

In this video, the structure of Earth is explored by examining both its compositional and mechanical properties. The presenter breaks down the Earth into layers: the crust (oceanic and continental), the mantle, and the core. The discussion covers the varying thicknesses and densities of these layers, as well as their mechanical characteristics, such as whether they are rigid, solid, or fluid. The video further explains the lithosphere, asthenosphere, mesosphere, and core, highlighting how temperature, pressure, and composition influence Earth's structure, and how tectonic plates move over the semi-fluid asthenosphere.

Takeaways

• 😀 The Earth's structure can be analyzed in two ways: compositional (chemical layers) and mechanical properties (solid, liquid, or semi-rigid layers).
• 😀 The Earth's crust is the outermost layer, consisting of oceanic and continental crust, with the continental crust being thicker and less dense than the oceanic crust.
• 😀 Oceanic crust is about 5-10 kilometers thick, while continental crust ranges from 10 to 70 kilometers thick.
• 😀 The mantle is the thickest layer of the Earth, extending about 2,900 kilometers below the crust and composed of different types of rock.
• 😀 The core is the densest part of the Earth, composed primarily of metals like iron and nickel.
• 😀 As you go deeper into the Earth, the density, heat, and pressure increase, with denser elements sinking to the core and lighter elements rising to the surface.
• 😀 The lithosphere includes the rigid outer layer of the Earth, made up of the crust and the uppermost part of the mantle.
• 😀 The lithosphere is divided into tectonic plates, which move on top of the asthenosphere, a semi-fluid layer of the mantle.
• 😀 The asthenosphere is a putty-like, semi-fluid layer that allows the lithospheric plates to move. It extends from the base of the lithosphere to about 660 kilometers deep.
• 😀 Deeper than the asthenosphere, the mesosphere is a solid, rigid layer due to extremely high pressure, despite the high temperatures.
• 😀 The Earth's core is split into the outer liquid core, which is composed of molten metals, and the solid inner core, which is also metallic but solid due to extreme pressure.

Q & A

What are the two perspectives from which the Earth's structure is analyzed in this video?

The Earth's structure is analyzed from two perspectives: the chemical or compositional layers on the left and the mechanical properties of the layers on the right.

What is the composition of the Earth's crust, and how is it divided?

The Earth's crust is divided into oceanic and continental crust. Oceanic crust is thinner (about 5-10 km thick) and denser, while continental crust is thicker (10-70 km) and less dense.

How thick is the Earth's mantle compared to the crust?

The Earth's mantle is much thicker than the crust, extending about 2,900 kilometers deep, whereas the crust is only 5 to 70 kilometers thick.

What is the core made of, and how does its composition differ from the mantle and crust?

The core is primarily made of metals, particularly iron and nickel. Its composition is fundamentally different from the mantle and crust, which are made up of rocky materials.

What are the two types of crust, and how do they differ?

The two types of crust are oceanic and continental. Oceanic crust is thinner, around 5 to 10 kilometers, and denser than continental crust, which is thicker (10 to 70 km) and less dense.

What is the lithosphere, and what does it consist of?

The lithosphere is the outermost, rigid layer of the Earth, made up of both the crust (continental and oceanic) and the uppermost part of the mantle.

What is the asthenosphere, and how does it differ from the lithosphere?

The asthenosphere is a layer below the lithosphere, characterized by rock that is not fully solid, but instead behaves like putty due to high temperatures and pressures. Unlike the rigid lithosphere, the asthenosphere allows for flow and convection.

At what depth does the asthenosphere begin, and how far does it extend?

The asthenosphere begins just below the lithosphere and extends down to about 660 kilometers deep.

What is the difference between the mesosphere and the asthenosphere in terms of their mechanical properties?

The mesosphere is a solid layer of the mantle, where the pressure is so high that even though temperatures are high, the rock is rigid. The asthenosphere, in contrast, is more fluid-like and behaves like putty due to lower pressures and slightly higher temperatures.

What is the composition of the Earth's core, and how does the outer core differ from the inner core?

The Earth's core is made primarily of metals, specifically iron and nickel. The outer core is liquid because the temperatures are high enough to melt the metals but the pressure is not sufficient to keep them solid. The inner core, however, is solid because the pressure is so great that even the metals remain solid despite high temperatures.