Science Questions

What keeps the Earth's core so hot?

Sun, 12th Oct 2008

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Glen asked:

What keeps the Earth's core so hot?



Chris - It's a combination of things. One, the earth's quite a big planet relative to Mars which is a bit smaller. There was a lot of heat that was in the Earth to start with. When the planets were first forming around the sun in what's called a protoplanetary disc a lot of the swirling and spinning material was crammed together and squeezed together. It had a lot of heat from that, those frictional effects. Also the Earth has what's loosely termed as radioactive compounds in the Earth. As these radioactive compounds break down and decay they produce heat. The heat is obviously concentrated in the core of the Earth and then filters up towards the surface. Because the Earth's a big planet it's got a big core. It's got lots of radioactive decay going on. Some of the heat that we're seeing is because the Earth is sustaining it's own heat by radioactive decay.

Kat - Like having a nuclear reactor in our core.


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glenn asked the Naked Scientists: Why doesn't the Earth's core ever cool down? What do you think? glenn, Fri, 3rd Oct 2008

Radiogenic heating, like in a nuclear power station. RD, Sat, 4th Oct 2008

Also, heat left over from the formation of the planet, but this is small in comparison to the heat produced by the radioactive reactions. rosnathan, Sat, 4th Oct 2008

My understanding is that it has cooled down, and used to be more active over the past 4.6 billion years. frethack, Sat, 4th Oct 2008

Yes, this is known as a "georeactor". The radioactive decay of various elements within the planet's interior produces heat. On the scale of a body as large as the Earth this adds up to a lot of energy, which helps to keep the core of the planet hot.

The same science is used to power space probes, particularly those which are venturing beyond the point at which solar panels could sustain them. The "New Horizons" mission to Pluto is one such example. The probes usually use isotopes of polonium and plutonium which decay so vigorously that they produce a lot of heat; this is connected to a thermocouple that turns the heat into electricity.

Chris chris, Sat, 4th Oct 2008

The abundance of potassium in the Earth's crust and mantle is significantly lower than in stoney meteroites.  Researchers suggest that the depleted potassium in the mantle/crust may have formed iron-potassium alloys in the core, postulating that potassium could be the major radioactive heat source in the core. Bass, Sat, 4th Oct 2008

Thanks Bass - I was wondering how the potassium, being quite light in the grand scheme of things, should get into the core.

Chris chris, Sun, 5th Oct 2008

Hey Bass, does this mean the earth will eventually explode due to becoming an argon balloon?

JimBob, Mon, 6th Oct 2008

Explanation of above question: 40K -> 40Ar

40K decays to stable 40Ar (11.2%) by electron capture and by positron emission, and decays to stable 40Ca (88.8%) by beta decay.

(for those with a scientific mind.) JimBob, Mon, 6th Oct 2008  RD, Mon, 6th Oct 2008

Thanks to the eminent professor JimBob, I now know that an atom of Ar takes up more space than an atom of K- in spite of radioactive decay.  Thanks for keeping that straight.  Of course, with a half life exceeding a billion years, this process may take a while?? Bass, Mon, 6th Oct 2008 

And to think I've wasted all these years on plate tectonics!
Bass, Mon, 6th Oct 2008

Because we don't understand how the energy at the core relates to the mass of the planet.

4 billion years old, one would think that aggressive radioactive decay would be all done and dusted by now.

Andrew K Fletcher, Mon, 6th Oct 2008

Not at all; radioactive decay is a stochastic process. Also, the products are themselves radioactive with variable half-lives.

Chris chris, Wed, 29th Oct 2008

the sun is like a big big in your microwave oven .a magnetron gives off micro waves.the waves move very fast. radio waves move a lot slower.the micro waver speed up molecules .when molecules move they make friction.witch cause heat.its like rubbing your two hands together very very fast.feel the heat.Lets get back to the sun.the sun gives off radiation . sorry for the spelling.i cant be good at everything.the radiation pass threw the earth and heat the iron core of the a micro wave oven.I will call it the radiation wave oven affect.LOL.did you ever stick metal in the micro wave sparks and heats up.thats what the earths core is doing.the radiation hits the earths magnetosphere and enters at the poles .the iron core molecules  start rubbing each other.causing heat.So thats how the earth core stays hot.the earth was hit buy the moon.and made the iron core.wright now the sun is getting god turned up his natreno wave oven on high.the sun will go back to its low setting . We are not having a global problems .this has been going on for 4 in a half billion years. So the sun goes from low to a micro wave oven.Now the government knows this.and trying to make us pay for it with the global warming act .vote no on the Act.This will be part 1# of my theses. theirs a lot more to talk about .the earth is heating up.the core is getting hotter .when core gets hot. the molten lava starts to expand from the heat.causing earth quakes and erupting volcanoes.last time this when Yellow stone caldera blow up.Now that took a lot of pressure to do that.So the government should find out how many times the caldera blown up.then they can predict the next one.      macgyver2112, Sun, 20th Dec 2009


No, you are an idiot, you have written rubbish, you then insulted me and you are now banned. Congratulations.

However, just to set the record straight, neutrinos interact with very little; they certainly do not interact with Earth sufficiently to account for the body of heat in the core. If that were true then Mars would also still have a hot core. As it stands, however, Mars appears to have cooled down back in time and consequently lost its magnetic field. Were neutrinos keeping Earth warm then why would they discriminate against Mars.

Meanwhile, if you do discover some manners and you are willing to write back to me and apologise for your behaviour, then I will unlock you user and reinstate you.

Thank you.

Chris Smith, Managing Editor. chris, Sun, 20th Dec 2009

Wow!  That 'part 1' really shows how dangerous a little knowledge can be, being wrong in just about every important respect. LeeE, Mon, 21st Dec 2009

Si, hombre JimBob, Tue, 22nd Dec 2009

Awe, c'mon now.  He did get one thing right.

Bass, Thu, 24th Dec 2009

Lol -  LeeE, Thu, 24th Dec 2009

Th aggressively radioactive elements have decayed. The ones that are still with us take billions of years to fall apart. The earth would cool down eventually, but the sun will go red giant first. Bored chemist, Sat, 2nd Jan 2010

Everything that moves sure has energy :) americanfridge, Mon, 18th Jan 2010

I have a theory, that in part the heat may be caused on account of the gravitational pull of the moon that causes the molten core to churn, just like the moon is responsible for tides in the oceans. Jai Misra, Sat, 31st Aug 2013

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