Internal heat from Earth’s formation and radioactive isotopes keep Earth’s core and mantle hot, enabling plate movement and life.
Our Earth is an onion-like structure, composed of various layers. Starting from the top, there is the crust, followed by the mantle, outer core, and finally the inner core. The deeper you dive, the hotter it gets, with parts of the core reaching temperatures as hot as the surface of the Sun. Scientists use seismic waves, or sound waves produced by earthquakes, to image the Earth’s internal structures. The lithosphere, which is the upper part of the mantle and the crust, is divided into large blocks called plates. These plates are like puzzle pieces that fit together and cover the surface of the Earth. They are not static and can move, sometimes as little as a fraction of an inch over a period of years, and other times more suddenly, triggering earthquakes and volcanic eruptions. Plate movement is essential for the evolution of life on Earth, as it changes the environment and forces life to adapt.
The heat within the Earth’s interior is not from the Sun, as it cannot penetrate through the miles of the planet’s interior. Instead, there are two sources: the heat that Earth inherited during its formation 4.5 billion years ago, and the decay of radioactive isotopes distributed everywhere in the Earth. The former was produced during the collisions and mergings between bits of rock and debris called planetesimals, and the latter is released from unstable isotopes of elements, such as uranium-235 and potassium-40.
Plate motion requires a hot mantle, and indeed, as you go deeper into the Earth, the temperature increases. At the bottom of the plates, around 60 miles (100 kilometers) deep, the temperature is about 2,400 degrees Fahrenheit (1,300 degrees Celsius). By the time you get to the boundary between the mantle and the outer core, 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). This is the part that’s as hot as the surface of the Sun.
Plate motion is essential for the evolution of life on Earth, as it changes the environment and forces life to adapt. Without the Earth’s internal heat, the plates would not have been moving and the Earth would have cooled down, making it uninhabitable. The heat from the Earth’s formation and the decay of radioactive isotopes provide the heat to drive the motion of the plates, which has been ongoing for billions of years. The plates also affect the atmosphere over similarly lengthy time scales, making it possible for life to thrive on Earth.
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