(PT) Layers of Earth Lesson

Layers of Earth

The Earth is composed of four different layers. Many geologists believe that as the Earth cooled the heavier, denser materials sank to the center and the lighter materials rose to the top. Because of this, the crust is made of the lightest materials (rock- basalts and granites) and the core consists of heavy metals (nickel and iron).

The crust is the layer that you live on, and it is the most widely studied and understood. The mantle is much hotter and has the ability to flow. The Outer and Inner Cores are hotter still with pressures so great that you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth!

What's inside the Earth?

In the early part of the 20th century, geologists studied the vibrations (seismic waves) generated by earthquakes to learn more about the structure of the earth's interior. They discovered that it is made up of these distinct layers: the crust, the mantle, and the core. These layers change in composition. The depth of the Earth's layer will make a difference in its composition, temperature and density. Temperature and density increases as depth increases.

Watch this video about the layers of the Earth.

Here is a diagram to help you understand the depths of each layer when comparing them to each other.

Depth Measurement

The crust - (0-100 km)

Mantle - (100 - 2900 km)

Outer core - (2900 - 5100 km)

Inner core - (5100 - 6378 km)

The Crust

The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. It makes up only one percent of the earth's mass. The crust is the upper part of the rigid lithosphere and is of different composition under land as opposed to the ocean floor. This consists of the continents and ocean basins. The crust has varying thickness, ranging between 35-70 km thick in the continents and 5-10 km thick in the ocean basins. The temperatures of the crust vary from air temperature on top to about 1600 degrees Fahrenheit (870 degrees Celcius) in the deepest parts of the crust. To get a feeling for this temperature understand you can bake a loaf of bread in your oven at 350 degrees Fahrenheit, at 1600 degrees Fahrenheit rocks begin to melt. The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, plastic mantle which is located below the crust. These plates usually move along smoothly but sometimes they stick and build up pressure. The pressure builds and the rock bends until it snaps. When this occurs an Earthquake is the result!

Look at the image and notice how thin the crust of the Earth is in comparison to the other layers. The seven continents and ocean plates basically float across the mantle which is composed of much hotter and denser material.

Mantle

MANTLE -- The mantle is a dense, hot layer of semi-solid rock approximately 2,900 km thick and is composed mainly of ferro-magnesium silicates. This is where most of the internal heat of the Earth is located. Large convective cells in the mantle circulate heat and may drive plate tectonic processes.

The mantle is one of the three main layers of the Earth. It lies between the innermost layer, the core, and the thin outermost layer, the crust. The mantle consists of hot, dense, semisolid rock, which slowly moves or flows, and is about 2,900 kilometers (1,802 miles) thick.

Layers of the mantle

• Lithosphere:The thin outermost shell of the upper mantle is similar to the crust, though cooler and more rigid. Together with the crust, this layer is called the Earth's lithosphere. The lithosphere is actually broken up into several large pieces, or plates. They "float" very slowly on a softer mantle layer called the asthenosphere.

• Asthenosphere: Their very slow motion is the cause of plate tectonics, a process associated with continental drift, earthquakes, and volcanoes, and the formation of mountains.

• Upper mantle. Below the asthenosphere lies another layer, stronger and more solid than the asthenosphere. All layers below the crust down to a depth of about 670 kilometers (416 miles) are known as the upper mantle.
• Lower mantle. The rest of the mantle between the upper mantle and the core is known as the lower mantle. It is denser and hotter than the upper mantle.

The Core

Earth's core is the very hot center of our planet. Heat from the mantle and core creates convection currents. It is made almost entirely of metal. The core is made of two layers:

The outer core is molten and borders the mantle, and the inner core is a dense solid.

Scientists say the outer core is made mostly of iron and nickel. Iron and nickel are two important metals found everywhere on the planet. (On the surface of the Earth, these metals are found in solid form.) Iron and nickel in the outer core form an alloy, or a mixture of metallic elements. The outer core is approximately 2,300 kilometers (1,430 miles) thick. The alloy of the outer core is very hot, between 4,000 and 5,000 degrees Celsius (7,200 and 9,000 degrees Fahrenheit).

Watch this video to learn more about Earth's outer core.

The inner core is shaped like a ball.

The inner core is made mostly of iron. It is approximately 1,200 kilometers (750 miles) thick. Although the iron is extremely hot—between 5,000 and 7,000 degrees Celsius (9,000 and 13,000 degrees Fahrenheit)—the pressure from the rest of the planet is so great that the iron cannot melt. For this reason, the inner core is mostly solid. Because the Earth has a ball of metal in the middle of it, the entire planet is magnetic. Scientists believe the liquid outer core is what controls the Earth's magnetic field. The magnetic field acts almost like a bubble. It protects the planet from charged particles floating around in the solar system, such as those from the sun. The magnetic North and South Poles are opposing sides of Earth's big magnet. The hard, metallic material in the core is balled up in the center of the Earth because it's the heaviest material on the planet. When Earth was formed about 4.5 billion years ago, all the heavier substances sank toward the middle. The lighter and less dense material, such as air and water, stayed closer to the crust. Inside the core, the metals are constantly moving. The core of the Earth rotates regularly. Some scientists say the inner core actually rotates faster than the rest of the planet!

Watch this video to learn more about the Earth's inner core.

Label the Layers of Earth

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