How does the interior of the Earth stay as hot as the surface of the Sun for billions of years?

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Our earth is like an onion – one layer after another.

There is a shell covering the surface you move from top to bottom; then lower, the mantle, mostly solid rock; then a deeper, outer core made of liquid iron; and finally an inner core made of solid iron with a radius 70% the size of the Moon. The deeper you go, the hotter it gets – parts of the core are as hot as the Sun’s surface.

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Journey to the center of the earth

Ace a professor of earth and planetary sciences, I study the inside of our world. Just like a doctor can use a technique sonography using ultrasound waves to take pictures of structures in your body, scientists use a similar method to image the interior of the Earth. But instead of ultrasound, geoscientists use it seismic waves – sound waves caused by an earthquake.

On the surface of the earth, of course, you see dirt, sand, grass, and pavement. Seismic vibrations reveal what lies beneath: large and small rocks. All of these are part of the Earth’s crust and can descend as low as 20 miles (30 kilometers); it floats on top of a layer called the mantle.

The upper part of the mantle usually moves with the crust. They are called together lithosphereit averages about 60 miles (100 kilometers) thick, although it can be thicker in some places.

The lithosphere is divided into several parts large blocks called slabs. For example, the Pacific plate underlies the entire Pacific Ocean and the North American plate covers most of North America. The plates are roughly like puzzle pieces that fit together and cover the Earth’s surface.

Tiles are not static; they act instead. Sometimes it’s just the tiniest fraction of an inch over several years. Other times there is more movement and more suddenness. Such movement causes earthquakes and volcanic eruptions.

The story continues

Moreover, plate motion is a critical and probably important factor in the evolution of life on Earth because moving plates change the environment and forces life to adapt to new conditions.

The heat is on

Slab motion requires a hot mantle. And indeed, the temperature increases as you go deeper into the Earth.

At the bottom of the plates, about 60 miles (100 kilometers) deep, the temperature is about 2,400 degrees Fahrenheit (1,300 degrees Celsius).

By the time you reach the boundary between the mantle and the outer core, 1,800 miles (2,900 kilometers) down, the temperature is about 5,000 F (2,700 C).

Then, at the boundary between the outer and inner cores, the temperature doubles to about 10,800 F (more than 6,000 C). It is part of it It is as hot as the surface of the sun. At this temperature, almost everything – metals, diamonds, people – turns into a gas. But because the core is under such high pressure deep inside the planet, the iron it is made of remains liquid or solid.

Collisions in space

Where does all this heat come from?

Not from the sun. Although it warms us and all the plants and animals on Earth’s surface, sunlight cannot penetrate for miles through the interior of the planet.

Instead, there are two sources. One of these is the heat that the Earth inherited during its formation 4.5 billion years ago. The earth was created from the solar nebulaa giant gaseous cloud between endless collisions and mergers between rock fragments and debris called planetesimals. This process took tens of millions of years.

These collisions generated enough heat to melt the entire Earth. While some of this heat was lost to space, the rest was trapped inside the Earth, and most of it remains there today.

Another source of heat: The decay of radioactive isotopes that are common throughout the Earth.

To understand this, first imagine an element like a family with isotopes as members. Each atom of a given element has the same number of protons, but different isotopic cousins ​​have different numbers of neutrons.

Radioactive isotopes they are not stable. They release a steady stream of energy that turns into heat. Potassium-40, thorium-232, uranium-235, and uranium-238 are four radioactive isotopes that keep the Earth’s interior warm.

Some of these names may sound familiar to you. For example, it is used as Uranium-235 fuel in nuclear power plants. The Earth is in no danger of running out of these heat sources: Although most the original uranium-235 and potassium-40 are gonethorium-232 and uranium-238 are enough to last for billions of years.

Along with the hot core and mantle, these energy-releasing isotopes provide the heat to keep the plates moving.

No heat, no plate motion, no life

Even now, the moving plates continue to change the surface of the Earth, constantly creating new lands and new oceans over millions and billions of years. Plates similarly affect the atmosphere over long periods of time.

But without the Earth’s internal heat, the plates would not move. The earth would have cooled. Our world would likely be uninhabitable. You wouldn’t be here.

Think about that the next time you feel the Earth beneath your feet.

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Written by: Shichun Huang, University of Tennessee.

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Shichun Huang does not work for, consult with, own stock in, or receive funding from any company or organization that would benefit from this article, and reports no affiliation outside of their academic designation.