This article was originally published on Conversation. (Opens in a new tab) The post contributed the article to Space.com Expert Voices: Editorial and Insights.
Xichun Huang (Opens in a new tab)Associate Professor of Earth and Planetary Sciences, University of Tennessee.
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.
Related: Layers of the Earth: Exploring Our Planet Inside and Out
The Journey to the Center of the Earth
Professor of earth and planetary sciences (Opens in a new tab)I study the insides of our world. Just as the doctor can use a technique called sonography (Opens in a new tab) 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 seismic waves — sound waves produced by earthquakes.
On Earth’s surface, you see dirt, sand, grass, and of course sidewalks. Seismic vibrations reveal what is below that (Opens in a new tab): 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 the lithosphere (Opens in a new tab)which is about 60 miles (100 km) thick on average, although it could be much thicker in some locations.
The lithosphere is divided into many large blocks called plates (Opens in a new tab). 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 force life to adapt to new conditions. (Opens in a new tab).
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 Fahrenheit (1,300 degrees Celsius).
By the time you reach the boundary between the mantle and the outer core, which lies 1,800 miles (2,900 kilometers) deep, the temperature is about 5,000 F (2,700 C).
Then, at the boundary between the outer and inner cores, the temperature doubles, reaching nearly 10,800 F (more than 6,000 C). This is the hot part of the sun’s surface. At this temperature, almost everything – minerals, diamonds, people – vaporizes into a gas. But because the core is under high pressure deep within the planet, the iron that makes it up remains liquid or solid.
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. The earth consists of a solar nebula (Opens in a new tab), a giant cloud of gas, amid endless collisions and mergers of bits of rock and debris 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 element as a family with isotopes as members (Opens in a new tab). Each atom of a given element has the same number of protons, but its different isotopic cousins have varying numbers of neutrons.
Radioactive isotopes (Opens in a new tab) not stable. They release a steady stream of energy, which is converted into heat. Potassium-40, Thorium-232, Uranium-235, and Uranium-238 are four of the radioactive isotopes that keep the Earth’s core warm.
Some of these names may sound familiar to you. Uranium-235, for example, is used as fuel in nuclear power plants. Earth is in no danger of running out of these heat sources: although most of the original uranium-235 and potassium are gone, there is enough thorium-232 and uranium-238 to last for billions of years.
Along with the hot core and mantle, these energy isotopes provide heat to drive plate motion.
No heat, no plate movement, no life
Even now, the moving plates continue to alter the Earth’s surface, constantly creating new lands and new oceans over millions and billions of years. (Opens in a new tab). Plates also affect the atmosphere over similarly long periods of time.
But without the Earth’s internal heat, the plates wouldn’t be moving. The earth may cool. Our world is probably uninhabitable. You won’t be here.
Think about it, next time you feel the ground under your feet.
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