I understand that the Earth’s core is full of very hot liquid rock, but why is it hot and why does it stay hot?
What is the heat source?
In: Planetary Science
It started off hot when the planet first came together and it stays hot through friction from the movement of the Earth itself.
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It started off as just the heat of rocks colliding together during the Earth’s formation.
Since they were flying through space, they had kinetic energy and gravitational potential energy with each other. When they collide and deform each other, they release that energy as heat.
That alone only gives the Earth enough heat to last a few million years before it cools to what we have now. The decay of radioactive elements gives the Earth enough heat to keep it warm enough to reach its current point after 4.6 billion years.
You know how if you rub something against a spring disc/ ball it gets hot? (Imagine brake pads or a baseball). For baseball it’s like 1 second of heat, earth is bigger so it’s more like millions of years.( I have no idea what I’m talking about)
Many others have given good answers, but there is also the moon and sun tugging on the earth via gravity. This also aids, albeit to what extent I am not sure, in heating the core.
There are four sources for heat at the Earth’s core
1 – Latent heat remaining from the formation of the earth.
2 – Radioactive decay of elements, which BTW is also the source of most helium found on Earth.
3 – Crystallization of iron in the Earths core releases heat.
4 – Heavier elements slowly sinking to the core converts potential energy into heat.
Most of the heat of the Earth’s core is left over from Earth’s formation.
All those chunks of rock banging together at high speed generated a lot of heat, and the crust of the Earth itself is an incredibly good insulator keeping all that heat in there.
Volcanoes and tectonic movement all serve to release that energy, but the total amount released is minuscule compared to how much is down there.
Another important factor is the Theia impact. It is currently believed that the moon was formed by the impact of a mars sized object with Earth. This re-liquefied much of the planet at a critical time in its formation and may explain why Earth’s core is still molten when similarly sized Venuses core is nearly solid.
Much of what makes Earth unique from our magnetic field, tectonic movement, the axial tilt (the seasons), the tides, and even the speed of the rotation are possibly all the result of our moon and how it was formed.
The Earth’s core also contains a lot of radioactive material like Thorium and Uranium. The constant radioactive decay of these materials is constantly re-heating the core.
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