# Will the center of the earth ever cool? **URL:** \ **Category:** Factual Questions\ **Created:** [March 11, 2002, 5:29pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619 "2002-03-11T17:29:37Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![LonesomePolecat](https://avatars.discourse-cdn.com/v4/letter/l/a88e57/32.png) [@LonesomePolecat](https://boards.straightdope.com/u/LonesomePolecat)\ **Post date:** [March 12, 2002, 2:42pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/21 "2002-03-12T14:42:13Z")
> [@](#): > > \*Originally posted by Steve MB \* > \*\* > As we now know (and as several people already mentioned), the earth’s internal heat is replenished by radioactive decay. Since the isotopes that provide the energy are long-lasting (the main contributors are thorium-232 with a half-life of 14 billion years and uranium=238 with a half-life of 4.5 billion years), the heat supply will diminish only a little over the life of the solar system. \*\* How did the radioactive materials get there? Are they or have they been at the core of all the planets (except the gas giants, of course)? ---
**Author:** ![Slip\_Mahoney](https://avatars.discourse-cdn.com/v4/letter/s/e47774/32.png) [@Slip\_Mahoney](https://boards.straightdope.com/u/Slip_Mahoney)\ **Post date:** [March 12, 2002, 3:40pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/22 "2002-03-12T15:40:46Z")
Actually, the gas giants also posses a solid core. ---
**Author:** ![SCSimmons](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@SCSimmons](https://boards.straightdope.com/u/SCSimmons)\ **Post date:** [March 12, 2002, 4:05pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/23 "2002-03-12T16:05:24Z")
> [@](#): > > \*Originally posted by LiquidLobotomy \* > \*\*Two questions: > > 1. How do we know that the earth has an iron core? > > 2. Is that core perfectly circular? \*\* Geez, you don’t hold back on the hard questions, do you? 🙂 On the first question, it depends what you mean by ‘know’. It’s predicted by current theories of the formation of the solar system, which are consistent with observed properties of the system as a whole, but probably not fully established. However, that particular prediction is also consistent with observed mechanical and magnetic properties of the Earth, so it has to be considered fairly well established. (For instance, the specific shape of the planet compared with the angular speed of its rotation and the gravitational and magnetic flux across its surface strongly suggests the existence of an iron core.) The second question I’ve never seen considered anywhere … I suspect that it would be an oblate spheroid, like the Earth itself. ---
**Author:** ![LiquidLobotomy](https://avatars.discourse-cdn.com/v4/letter/l/898d66/32.png) [@LiquidLobotomy](https://boards.straightdope.com/u/LiquidLobotomy)\ **Post date:** [March 12, 2002, 4:36pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/24 "2002-03-12T16:36:35Z")
Nice work SCSimmons! I know we can’t truly “know” what the core is composed of, but if the majority of the evidence points to an iron core I’m all for it. I’m pretty sure that the earth isn’t a perfect sphere, but considering that the core is liquid, and gravity is pressing down equally, isn’t it a safe assumption that the core is perfectly circular? And before the pig pile starts- I know that when you assume you make an ass out of u and me. ---
**Author:** ![GreyMatters](https://avatars.discourse-cdn.com/v4/letter/g/a9a28c/32.png) [@GreyMatters](https://boards.straightdope.com/u/GreyMatters)\ **Post date:** [March 12, 2002, 5:09pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/25 "2002-03-12T17:09:58Z")
Current Theory holds: The Big Bang produce Hydrogen, Helium and a tiny bit of Lithium. The first stage of a Stars life is sustained by a Fusion process that converts the Hydrogen into more Helium. The Red Giant stage converts this material into all the elements from Lithium to Lead. The Star could die completely at this stage, but sometimes it is big enough to go into a rather short cycle of Fusion that ends in a Super Nova. In the Super Nova Stage ALL the Elements from Lithium on up to the last element on the Peridic Chart are created. This is the only known place that the elements larger than Lead are created. This includes the radioactive elements. This is how the modern theory holds that at least some of the matter in our solar system came from the explosion of a Super Nova. So, the radioactive elements came from the elxplosion of a Super Nova. So did the nickel and copper in the change in your pocket. ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [March 12, 2002, 5:38pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/26 "2002-03-12T17:38:43Z")
> [@](#): > > _Originally posted by LiquidLobotomy \* > \*\* > I’m pretty sure that the earth isn’t a perfect sphere, but considering that the core is liquid, and gravity is pressing down equally, isn’t it a safe assumption that the core is perfectly circular?_\* Probably not. Like SCS said, it’s probably an oblate spheroid (bulging at the equator) like the earth itself, due to its spin. Don’t forget that it’s not just sitting there perfectly still–it’s spinning, which causes deformation. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 12, 2002, 5:53pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/27 "2002-03-12T17:53:17Z")
> [@](#): > > The Red Giant stage converts this material into all the elements from Lithium to Lead. The Star could die completely at this stage, but sometimes it is big enough to go into a rather short cycle of Fusion that ends in a Super Nova. Actually, it’s everything up to iron, not lead. And I’m pretty sure that all of the lithium is primordial, with none made in stars. And speaking of iron, the probable reason that Mars has such a weak magnetic field is that it seems to be poorly differentiated for some reason. While most of the iron in the Earth is at the core (the stuff we mine largely comes from ancient asteroid impacts), Mars’ iron seems to be distributed pretty uniformly through the planet. Hence, all the red rocks at the surface. ---
**Author:** ![Drew\_Blade](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Drew\_Blade](https://boards.straightdope.com/u/Drew_Blade)\ **Post date:** [March 12, 2002, 6:34pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/28 "2002-03-12T18:34:08Z")
My hypothesis is that the core of the earth will never cool. I don’t have any formulas or figures to back me up, but the kindergarten-level reasoning behind the hypothesis is “Because it’s down”. On a slightly more explanatory level is this: It takes energy to move matter out of a gravity well. Light loses energy when it climbs out of a gravity well. Why should heat get a free pass? Unless there is something going on that I don’t see, heat will tend to gather inside heavy masses and stay there forever. I won’t attempt to figure how the 2nd law of thermodynamics interacts with this amazing hypothesis . . . ---
**Author:** ![Nukeman](https://avatars.discourse-cdn.com/v4/letter/n/ce7236/32.png) [@Nukeman](https://boards.straightdope.com/u/Nukeman)\ **Post date:** [March 12, 2002, 7:04pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/29 "2002-03-12T19:04:25Z")
> [@](#): > > \*Originally posted by Sam Stone \* > \*\*As I recall, the core of Mars has cooled and is now solid, which is why Mars doesn’t have a magnetic field. \*\* The core of mars may be solid, but I don’t see why that would get rid of its magnetic field. ---
**Author:** ![GreyMatters](https://avatars.discourse-cdn.com/v4/letter/g/a9a28c/32.png) [@GreyMatters](https://boards.straightdope.com/u/GreyMatters)\ **Post date:** [March 12, 2002, 7:27pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/30 "2002-03-12T19:27:47Z")
Thanks. I always mix those two up. Iron and Lead that is. Granted my limited knowledge, I do think that some lithium is created in stars by the fusion of hydrogen with helium. I could be wrong, but that’s what I remember the books telling my thick head. 🙂 ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [March 12, 2002, 7:36pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/31 "2002-03-12T19:36:53Z")
> [@](#): > > \*Originally posted by So Far So Good \* > \*\* > On a slightly more explanatory level is this: It takes energy to move matter out of a gravity well. Light loses energy when it climbs out of a gravity well. Why should heat get a free pass? Unless there is something going on that I don’t see, heat will tend to gather inside heavy masses and stay there forever. \*\* But everything outside is cold–so the heat in the core will eventually heat the mantle, which is a bit cooler, which will eventually heat the crust, which will eventually radiate its heat out into the void of space, until the whole planet reaches a nice, uniform, 3 degrees Kelvin like the rest of the universe (or possibly somehwhat colder by that time). ---
**Author:** ![Drew\_Blade](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Drew\_Blade](https://boards.straightdope.com/u/Drew_Blade)\ **Post date:** [March 12, 2002, 8:55pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/32 "2002-03-12T20:55:46Z")
But **toadspittle** , my whole point is that heat energy cannot climb out of a gravitational field without doing “work” and losing energy. The only place that energy can go is into heat that remains behind. If you postulate a planet without gravity I’m with you 100 %. 😃 ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [March 12, 2002, 9:40pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/33 "2002-03-12T21:40:16Z")
> [@](#): > > But toadspittle, my whole point is that heat energy cannot climb out of a gravitational field without doing “work” and losing energy. I don’t know that this is true. I’ve never heard that particular statement before. But while we’re talking about a gravity field here, we’re not talking about a singularity. Energy DOES escape from gravity wells all the time. Hence sunlight, radio waves from the earth traveling into outer space, etc. We’re in the gravity well right now. Show me how we aren’t beaming transmissions from Mission Control to the Space Shuttle or the Mars Odyssey probe, and I’ll believe your statement that heat energy (infrared radiation) can’t “climb” out of a gravitational field. ---
**Author:** ![Drew\_Blade](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@Drew\_Blade](https://boards.straightdope.com/u/Drew_Blade)\ **Post date:** [March 12, 2002, 10:42pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/34 "2002-03-12T22:42:21Z")
> [@](#): > > \*Originally posted by toadspittle \* > \*\* > But while we’re talking about a gravity field here, we’re not talking about a singularity. Energy DOES escape from gravity wells all the time. Hence sunlight, radio waves from the earth traveling into outer space, etc. We’re in the gravity well right now. Show me how we aren’t beaming transmissions from Mission Control to the Space Shuttle or the Mars Odyssey probe, and I’ll believe your statement that heat energy (infrared radiation) can’t “climb” out of a gravitational field. \*\* True enough. I agree the earth will cool down. I only meant to say that it will not cool as much as it would in the absence of a gravitational field. I do not see how it can ever reach 3 degrees Kelvin (or whatever temp the universe outside of gravity wells reaches) while gravity remains an effective force. ---
**Author:** ![GreyMatters](https://avatars.discourse-cdn.com/v4/letter/g/a9a28c/32.png) [@GreyMatters](https://boards.straightdope.com/u/GreyMatters)\ **Post date:** [March 12, 2002, 11:15pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/35 "2002-03-12T23:15:15Z")
Bluntly, a warm body of, non-singularity mass, without any influx of energy, will cool to the Universes mean temperature, given enough time. This is independant, and unaffected, by the Gravitational Field of the object. Hawking even theorizes that Singularities will eventually cool to the mean temp of the Universe when the mean temp drops below the mean temp of the Singularity. Thermodynamics is an extremely complex and powerful beast. Your misconception is caused by the difficulties in understanding Relativity. I can fully appriciate this, since I do not come any where near understanding Relativity. I do not have the time to regurgitate what little I have read so I will sit and hope someone else, smarter than I, will help explain this to us. Chronos? ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [March 13, 2002, 3:00am UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/36 "2002-03-13T03:00:25Z")
**Nukeman:** A planet’s magnetic field is caused by the motion of material in a liquid core made of conductive material. If the core is solid, then there is no relative motion of conductive material, and no way to regenerate the magnetic field. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [March 13, 2002, 5:28am UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/37 "2002-03-13T05:28:21Z")
> [@](#): > > \*Originally posted by k2dave \* > Remember that current theory is that the moon was part of the earth and broken off when a object hit the earth. So the moon is younger then mars and made of lighter material (upper earth stuff) instead of the heavier stuff that would form in hte planets I don’t think that the age difference is significant compared to the age of the planets. The last I heard, the Moon formed about 4.3 billion years ago, compared with 4.6 for the Earth and Mars. Not much of a difference. As far as the Moon being made of lighter materials, normally you would think that that would favor Mars in terms of radioactivity. After all, uranium has a very high density. But perhaps not. Uranium has a certain chemical affinity for lighter elements which is why it’s not all at the Earth’s core right now. And one of the important long-half-life radioactive elements is potassium which is fairly light compared with iron. But balance that all against the fact that Mars has 5 times as much mass as the Moon. Obviously there are a number of factors to consider when estimating the cooling rate of a planetary core. I’m not an expert, but it would not surprise me that the tidal flexing the Moon gets is perhaps the most significant factor. ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [March 13, 2002, 7:04am UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/38 "2002-03-13T07:04:10Z")
With tongue firmly in cheek, The answer is no. The half-life of the elements keeping the home fires burning are of a sufficient length that the Sun will run our poor asses over before those nuclear decay fires burn out. Did I get the answer right? ---
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [March 13, 2002, 12:48pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/39 "2002-03-13T12:48:40Z")
“On a slightly more explanatory level is this: It takes energy to move matter out of a gravity well. Light loses energy when it climbs out of a gravity well. Why should heat get a free pass?” It doesn’t. Electromagnetic radiation, including infrared, is gravitationally red-shifted when climbing out of a gravity well. The gravitational red shift is trivial for the Earth, or even a normal star like the Sun – it only starts to become significant for white dwarfs and other such superdense objects. “Unless there is something going on that I don’t see, heat will tend to gather inside heavy masses and stay there forever.” The gravitational red shift may reduce the amount of energy radiated from an object, but doesn’t stop it altogether unless the object collapses all the way to a black hole. Thus, objects warmer than the cosmic background still cool down over time. ---
**Author:** ![LiquidLobotomy](https://avatars.discourse-cdn.com/v4/letter/l/898d66/32.png) [@LiquidLobotomy](https://boards.straightdope.com/u/LiquidLobotomy)\ **Post date:** [March 13, 2002, 1:45pm UTC](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619/40 "2002-03-13T13:45:15Z")
> [@](#): > > \*Originally posted by toadspittle \* > \*\* > > Probably not. Like SCS said, it’s probably an oblate spheroid (bulging at the equator) like the earth itself, due to its spin. Don’t forget that it’s not just sitting there perfectly still–it’s spinning, which causes deformation. \*\* Shoot, you’re right! I completely forgot that the earth spins around…Doh! Thanks [Previous page](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619.md?page=1) [Next page](https://boards.straightdope.com/t/will-the-center-of-the-earth-ever-cool/97619.md?page=3)