One of those questions that get lodged in your brain and is unable to shake off. “Why is earth’s center so hot?”. Must be a lazy Monday evening, as I have spent the better part of the last hour or more thinking about and researching this one question. Well, one thing led to another and I learned a couple of useful things along the way, which I will share towards the end.
Coming back to the question at hand. I know it doesn’t make a whole lot of sense to compare the heat that the sun (star) generates vs the heat being generated inside the earth’s (planet) various cores. From what I know about how the sun operates, basically you have this giant ball of hydrogen, and the and the enormous weight/mass pulls on itself. This is what gives the sun and pretty much all the other planets it’s spherical shape. At this point I am going to steal the actual description of what’s going on inside the sun from this website as they have been able to summarize quite well in one paragraph, what I will probably take a page to describe:
If you could travel down into the Sun, you’d reach a point where the pressure and temperature are enough that nuclear fusion is able to take place. This is the process where protons are merged together into atoms of helium. It can only happen in hot temperatures, and under incredible pressures. But the process of fusion gives off more energy than it uses. So once it gets going, each fusion reaction gives off gamma radiation. It’s the radiation pressure of this light created in the core of the Sun that actually stops it from compressing any more.
Interesting stuff. Now having looked at the basics of how a star powers itself up. Let’s focus on our good ol Planet earth. A 4.5+ billion year old piece of rock that is pretty hot inside. 4.5+ billion years is a long time. The age of the universe is determined to be anywhere from 12 to 14 billion years ago. So this particular solar system that we dwell upon, formed along the way, approximately 66% into the universe’s existence to date. Meaning from the big bang till now (not the overall existence.) Again, 4.5 billion years is a long time and yet the center of the earth remains quite hot. Why?
Image and text (excerpt below): Courtesy of physorg
I will steal from physorg to be able to shed more more light on this subject:
“We don’t think this original heat is a major part of the Earth’s heat, though,” Marone says. It only contributes 5 to 10 percent of the total, “about the same amount as gravitational heat.”
Referring to the time when the earth first came into existence, well along with the better part of the solar system itself.
and then to build on the heating bit:
For all this, however, Marone says, the vast majority of the heat in Earth’s interior—up to 90 percent—is fueled by the decaying of radioactive isotopes like Potassium 40, Uranium 238, 235, and Thorium 232 contained within the mantle. These isotopes radiate heat as they shed excess energy and move toward stability. “The amount of heat caused by this radiation is almost the same as the total heat measured emanating from the Earth.”
So we started with a simple question. Then drew parallels between a sun and a planet and their ability to generate heat in a cold universe. Interesting stuff eh?
Some of the other stuff I was referring to earlier on, worth thinking about: