Earth’s surface heat from the inside – how did it stay that way for billions of years?

The slice you see cut from the ground reveals its core, shown here in bright yellow. Organized into layers similar to an onion, our Earth consists of a crust, mantle, outer core, and inner core, each with its own characteristics.

How did the Earth’s core stay as hot as the Sun’s surface for billions of years?

Earth’s layered structure, which includes moving plates, is heated by leftovers from planet formation and the decay of radioisotopes. Geologists use seismic waves to study these internal structures and motions, which are essential to environmental changes and the evolution of life on Earth. Internal heat drives plate motions, contributing to phenomena such as earthquakes, volcanic eruptions, and the creation of new lands and oceans, making Earth habitable.

Our Earth is made up sort of like an onion – layer by layer.

Starting from top to bottom, there is the cortex, which includes the surface you walk on; then down below, the mantle, mostly hard rock; then deeper, the outer core, made of liquid iron; Finally, the inner core, made of solid iron, with a radius of 70% of the volume of the Moon. The deeper you dive, the hotter it gets – parts of the core are as hot as the surface of the sun.

The layers of the Earth's illustration are annotated

This illustration shows the four subsurface sections.

The Journey to the Center of the Earth

K Professor of Earth and Planetary SciencesI study the insides of our world. Just like a doctor can use a technique called Sonography To make pictures of the structures inside your body using ultrasound, scientists use a similar technique to imaging the internal structures of the Earth. But instead of ultrasound, geoscientists use it seismic waves Sound waves generated by earthquakes.

On Earth’s surface, you see dirt, sand, grass, and of course sidewalks. Seismic vibrations reveal what is below that: large and small rocks. This is all part of the crust that may go down as far as 20 miles (30 kilometers); It floats above a layer called the mantle.

The upper part of the mantle usually moves with the crust. Together, they are called Lithospherewhich is about 60 miles (100 km) thick on average, although it could be much thicker in some locations.

The lithosphere is divided into several Large blocks are called plates. For example, the Pacific Plate lies under the entire Pacific Ocean, and the North American Plate covers most of North America. The panels are like puzzle pieces that roughly fit together and cover the surface of the Earth.

The panels are not fixed. Instead, they move. Sometimes it’s the smallest fraction of inches over a period of years. Other times, there is more movement, and it is more sudden. This type of movement is what causes earthquakes and volcanic eruptions.

What’s more, plate motion is a critical, and perhaps necessary, factor driving the evolution of life on Earth, because moving plates change the environment and Forcing life to adapt to new conditions.


You will be amazed at all the life that is happening under your feet.

The heat is on

Plate movement requires a heated cloak. Indeed, as you go deeper into the ground, the temperature increases.

At the bottom of the plates, at a depth of about 60 miles (100 kilometers), the temperature is about 2,400 degrees.[{” attribute=””>Fahrenheit (1,300 degrees Celsius).

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

Then, at the boundary between outer and inner cores, the temperature doubles, to nearly 10,800 °F (over 6,000 °C). That’s the part that’s as hot as the surface of the Sun. At that temperature, virtually everything – metals, diamonds, human beings – vaporizes into gas. But because the core is at such high pressure deep within the planet, the iron it’s made up of remains liquid or solid.


Without plate tectonics, humans probably wouldn’t exist.

collision in outer space

Where does all this heat come from?

It is not from the sun. While it warms us and all plants and animals on Earth’s surface, sunlight cannot penetrate miles of the planet’s interior.

Rather, there are two sources. One is the heat inherited by the Earth during its formation 4.5 billion years ago. Earth is made from the solar nebula, a giant cloud of gas, amid endless collisions and mergers of bits of rock and debris. They are called planetesimals. This process took tens of millions of years.

An enormous amount of heat was produced during those collisions, enough to melt the entire Earth. Although some of this heat was lost to space, what was left of it was trapped inside the Earth, where much of it remains today.

Another source of heat: the decay of radioactive isotopes, which are ubiquitous on Earth.

To understand this, first imagine an item As a family with isotopes as its members. all[{” attribute=””>atom of a given element has the same number of protons, but different isotope cousins have varying numbers of neutrons.

Radioactive isotopes are not stable. They release a steady stream of energy that converts to heat. Potassium-40, thorium-232, uranium-235, and uranium-238 are four of the radioactive isotopes keeping Earth’s interior hot.

Some of those names may sound familiar to you. Uranium-235, for example, is used as a fuel in nuclear power plants. Earth is in no danger of running out of these sources of heat: Although most of the original uranium-235 and potassium-40 are gone, there’s enough thorium-232 and uranium-238 to last for billions more years.

Along with the hot core and mantle, these energy-releasing isotopes provide the heat to drive the motion of the plates.

No heat, no plate movement, no life

Even now, the moving plates keep changing the surface of the Earth, constantly making new lands and new oceans over millions and billions of years. The plates also affect the atmosphere over similarly lengthy time scales.

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

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

Written by Shichun Huang, Associate Professor of Earth and Planetary Sciences, University of Tennessee.

Adapted from an article originally published in The Conversation.The Conversation

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