How, over the course of billions of years, has the inside of the Earth remained as heated as the Sun’s surface?

Similar to an onion, our Earth is composed of successive layers.

Starting from the top, there is the crust, which is the area you can walk on, followed by the mantle, which is primarily made of solid rock, the outer core, which is composed of liquid iron, and finally the inner core, which is composed of solid iron and has a radius that is 70% larger than the Moon’s. Parts of the core are as hot as the surface of the Sun as you descend deeper and deeper.

a representation of the Earth’s structure, including the crust, mantle, inner core, and outer core.
The four regions that make up the Earth’s interior are shown in this graphic.

using eliflamra/iStock images from Getty Plus

Explore the Earth’s interior
I research the inside of our planet in my capacity as a professor of earth and planetary sciences. Scientists utilize a similar approach to photograph the interior structures of the Earth, just as a doctor may use sonography to create images of the structures within your body using ultrasound waves. Geoscientists, however, employ seismic waves, which are sound waves generated by earthquakes, as opposed to ultrasonography.

Of course, there is pavement, grass, sand, and soil on the Earth’s surface. Rocks of different sizes may be seen below thanks to seismic tremors. All of this is a component of the crust, which may extend down as deep as 20 miles (30 kilometers); it floats on top of the mantle layer.

Usually, the crust and top section of the mantle move in unison. They are collectively referred to as the lithosphere, which is generally around 60 miles (100 kilometers) thick, though it can be thicker in some places.

Plates are the several enormous building components that make up the lithosphere. For instance, the North American plate covers the majority of North America whereas the Pacific plate is beneath the whole Pacific Ocean. The Earth’s surface is made up of plates, which approximately fit together like jigsaw pieces.

The plates are not still; they are in motion. Over the course of years, it can occasionally be the smallest percentage of inches. Sometimes the movement is more pronounced and abrupt. Eruptions of volcanic ash and earthquakes are caused by this type of movement.
Furthermore, because moving plates alter the environment and compel life to adapt to new circumstances, plate movement is a crucial and perhaps fundamental aspect in the evolution of life on Earth.

You’ll be astounded at the amount of life that exists beneath your feet.
The mantle must be heated for plate motion to occur. And it is true that the temperature rises as you descend more into the Earth.

The temperature is around 2,400 degrees Fahrenheit 60 miles (100 kilometers) below the surface of the plates (1,300 degrees Celsius).

The temperature is over 5,000 F by the time you reach the outer core-mantle border, which is 1,800 miles (2,900 kilometers) below the surface (2,700 C).
The temperature then almost doubles to 10,800 F at the inner-outer core border (over 6,000 C). That area is equally heated to the surface of the Sun. Almost everything vaporizes into gas at such temperature, including metals, diamonds, and living things. The iron in the core, however, is still liquid or solid because of the immense pressure it is under deep inside the globe.

Humans most likely wouldn’t exist without plate tectonics.
Interplanetary collisions Where does all that heat originate from?

It’s not the Sun, either. Sunlight can only reach a few miles into the planet’s interior, warming us and all the plants and animals on the surface.

There are two sources instead. One is the heat that Earth acquired from the sun when it formed 4.5 billion years ago. Planetesimals, or little pieces of rock and debris, constantly collided and merged in the solar nebula, a vast gaseous cloud, to create the Earth. Tens of millions of years passed throughout this procedure.

During such encounters, a tremendous quantity of heat was generated—enough to melt the whole Earth. While some of the heat was lost to space, the majority remained trapped inside the Earth, where it is still mostly present today.

The decay of radioactive isotopes, which are present all across the Earth, is the second source of heat.

To comprehend this, first think of isotopes as members of an element’s family.The number of protons is constant throughout an element’s atomic structure, whereas the amount of neutrons varies amongst its several isotope relatives.

Isotopes that are radioactive are unstable. They continuously emit energy, which is then transformed into heat. Four radioactive isotopes, namely potassium-40, thorium-232, uranium-235, and uranium-238, are responsible for maintaining the Earth’s interior’s heat.

Some of those names could be recognizable to you. Nuclear power facilities, for example, employ uranium-235 as fuel. These thermal energy sources on Earth are not in risk of running out: There is still enough thorium-232 and uranium-238 to persist for billions of years even though most of the initial potassium-40 and uranium-235 are no longer present.

These heat-releasing isotopes supply the heat necessary to propel the motion of the plates together with the heated core and mantle.

Without heat, plate motion, and life
Even now, the shifting plates continue to alter the Earth’s surface, continuously creating new continents and oceans over millions and billions of years. Over eons of time, the plates also have an impact on the atmosphere.

However, the plates would not have been moving if not for the heat produced by the Earth itself. It would have become cooler on Earth. Most likely, our planet would have been inhospitable. You wouldn’t be here, then.

The next time you feel the ground beneath your feet, consider that.
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