I was about 13 years old when teacher in school was explaining different hypothesis about Solar System and Earth formation and I couldn’t understand anything he is talking about, of course now I blame teacher for this ;-) For all those who is currently wondering why the heck it’s hot inside the Earth I will give some short and simple explanations, which could be true and could be not true (and there is no way to say which one is correct, that’s the fun part about science).
Hypothesis 1. When Solar System was forming there was a lot of small asteroid like bodies collisions which heated the material, also as proto-Earth was compressing with gravitational force it was warming up because of it (if you compress something it will heat up, trust me on this one ;-). By the time Earth formed it was hot, a piece of magma if you like. Time was passing by and Earth was cooling, by now it is cold enough on the surface for us to live on (but still hot inside), it will become even colder with time (do not confuse with global warming, we are talking about temperature inside the Earth here).
Proto-Earth could look something like this. Image Credit: Marco Fulle.
Hypothesis 2. There are some radioactive materials inside the Earth. What makes material a radioactive one? It’s atoms break with time for no reason. Let’s say you have an atom of radioactive material, after some time kaboom happens and atom breaks emitting a particle and some energy. The idea is that this emitted energy heats up the Earth. One more thing needs to be mentioned here, because some people think that there is not enough radioactive energy to heat the big mother Earth.
Amount of emitted energy depends on Earth volume (we are assuming that radioactive materials are spread in the Earth’s volume). Amount of energy emitted by Earth into space depends on Earth’s surface area. Volume depends on cubic radius and surface area depends on square radius, which means that even if we have a tiny amount of radioactive energy emitted inside the Earth heat will build up faster than than Earth will cool itself by emitting it’s heat to space (R3 >> R2 if R is big enough). It’s like barbecue — even a small fire will heat it up pretty well if you close the top cover.
Radioactive decay. Image credit: U.S. NRC
Hypothesis 3. It’s Moon who heats up the Earth! This one is pretty simple — Moon deforms the Earth a little bit with it’s gravity and it causes friction inside Earth which causes heat. The strong point of this hypothesis is that we have a good example of such process — it’s Io, Jupiter’s moon. It is very close to giant planet and it’s really hot because of constant deformations caused by it. I think it’s the second hottest space body in a Solar system after the Sun itself.
Io, Jupiter's moon, artist's impression. Image credit in the top right corner of image itself :-)
Which one of three do you like most? Or maybe you have your own?
Tags: astronomy, Earth, Earth core, Earth heat, magma, proto-Earth
July 9, 2009 at 11:52 pm |
I think a major factor is pressure. As the pressure increases the temperature goes up.
I know pV=nRT applies to gasses and that the center of the earth is solid/liquid iron and nickel, but I suspect that something similar holds though solids and liquids are less compressible than gasses.
July 10, 2009 at 10:05 am |
Yes, I can see how pressure could cause the initial heat, but Earth is quite old, why is it still hot?
I don’t think Earth compresses anymore in our days, so pressure does not produce any new heat and the initial heat should be emitted to space already.
Another hypothesis I didn’t mention in the post is that Earth dwarves need heat for their blacksmithing, so they burn a lot of coil inside our planet :-)
July 13, 2009 at 4:10 am |
[...] Ivan Pankov at ScienceAround.com has a new blog and this is his first submission to the Carnival. Congratulations Ivan! It’s about different models for Earth’s internal heat. [...]
October 15, 2009 at 5:36 pm |
Creation is the answer!