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Author Topic: Why is the earths core still hot?  (Read 5760 times)

Offline salt

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Why is the earths core still hot?
« on: 25/07/2011 20:19:21 »
I believe it is because the moon and the earths core are tidally locked causing the heating and the earths magnetic field also.


 

Offline CliffordK

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Why is the earths core still hot?
« Reply #1 on: 25/07/2011 20:36:53 »
There have been many theories about the origin of the heat in the Earth's core, including nuclear decay.

This article uses a novel approach to estimate the amount of continuing nuclear fission in the earth's core, and estimates that about half of the core heat is due to ongoing nuclear fission and decay.  Actually, I'm not sure if they differentiated between fission and ordinary nuclear decay.

It also takes a very long time to cool down a chunk of rock the size of Earth, and some of the heat is likely primordial heat that has been slowly dissipating over the last 4 to 5 billion years.  I'm sure that a relatively dense atmosphere and a relatively warm surface doesn't help either.

As you mentioned, gravity from both the sun and the moon, as well as the sun's magnetic field likely also influence the differential movement between the crust and the core, and generates additional heat.
 

Offline salt

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Why is the earths core still hot?
« Reply #2 on: 26/07/2011 15:42:23 »
nuclear decay? if the whole core started completely made of a substance with a 10,000 year half life how much would be left?
 

Online syhprum

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Why is the earths core still hot?
« Reply #3 on: 26/07/2011 21:41:15 »
The heavy isotopes that generate the heat have a much longer half life
 

Offline Soul Surfer

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Why is the earths core still hot?
« Reply #4 on: 28/07/2011 19:09:40 »
The main heating isotopes nowadays have extremely long half lives one of the main ones u238  has a half life of 4.5 billion years  just about the age of the earth.
 

Offline Mr. Data

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Why is the earths core still hot?
« Reply #5 on: 28/07/2011 19:17:10 »
What is it called again... gravitional induction, or something along those lines? Or gravitational friction... I cannot google, in a rush... but basically gravitational effects inside the earth generates heat from kinetic influence of particles. Plus natural egnitions, and kinetic influences contribute to the heat of the core of the earth. In other words, it is a volatile place from local and non-local events.
 

Offline Bored chemist

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Why is the earths core still hot?
« Reply #6 on: 29/07/2011 14:48:54 »
What is it called again... gravitional induction, or something along those lines? Or gravitational friction... I cannot google, in a rush... but basically gravitational effects inside the earth generates heat from kinetic influence of particles. Plus natural egnitions, and kinetic influences contribute to the heat of the core of the earth. In other words, it is a volatile place from local and non-local events.
Do you have some other "other words", preferably some that are clearer?
 

Offline damocles

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Why is the earths core still hot?
« Reply #7 on: 02/08/2011 15:47:31 »
I believe that the consensus among Earth scientists is that the interior of the Earth is warmed by three main effects, with others possible.

1. Residual heat from the gravitational collapse that formed the Earth in the first place. A few thousand kilometres of rock is a pretty good insulator.
2. Natural radioactive decay, nearly all from U-238 and Th-232. (K-40 generates as much radiation, but much less heat because its radiations are very low energy ones)
3. Tidal friction. The gravitational effects of the sun and the moon cause a significant amount of flexion of the rocks, which produces frictional heat.

Not all sources agree on the relative importance of these three factors, though 3 is generally reckoned to be a rather smaller effect than 1 or 2.

Here is one fairly reputable evaluation: http://en.wikipedia.org/wiki/Geothermal_gradient

The fact that the Moon and Mars do not have molten cores is fairly strong evidence that factor 2 does not dominate, and 1 or 3 must play a major role.

The Galilean Moons of Jupiter, particularly Io and Europa, are subject to the huge gravitational field of the central planet, and for these factor 3 is clearly responsible for their atypical warmth.
 

Offline imatfaal

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Why is the earths core still hot?
« Reply #8 on: 02/08/2011 16:50:13 »
Damocles - great answer.  All makes a lot of sense - and ties in with one of my favourite factoids. 

Darwin's theory of evolution by natural selection was initially in real problems (not merely due to the Luddite religious mafia) because the age of the earth - as calculated by Lord Kelvin - was maxed out at about 40 million years and this was not nearly enough.  Kelvin based his figures on the time an absolutely molten sphere would take to cool to how it is now (or then) - but Kelvin was neglecting (not surprisingly) the effects of radiative decay.  Kelvin's figures were backed up by others who estimated age of the sun to be about the same (those guys were just using gravitational heating not solar hydrogen fusion).  Of course we know now that other effects have influenced the heat of the earth - and there is plenty of time for evolution through natural selection. 
 

Offline chris

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Why is the earths core still hot?
« Reply #9 on: 02/08/2011 17:18:41 »
I gave quite a thorough answer to this question in a recent episode of the podcast. This is a link to the transcript:

http://www.thenakedscientists.com/HTML/content/latest-questions/question/3031/

Chris
 

Offline CPT ArkAngel

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Why is the earths core still hot?
« Reply #10 on: 02/08/2011 17:28:19 »
Does someone know about the radioactive decay rate reduction over time inside the earth?
 

Offline CPT ArkAngel

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Why is the earths core still hot?
« Reply #11 on: 02/08/2011 17:40:46 »

 

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