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View Full Version : How long will it take for Earths core to cool?



Civilshock
2009-Dec-02, 07:54 AM
Hypothetically if our Sun were to last for millions of trillions of years, how long would it take for Earths core to cool until its essentially just a big cold space rock?

astromark
2009-Dec-02, 09:56 AM
I do not think it would ever get cold. At some point the gravitational forces acting on the mass of the Earth... Deep within the core of Earth the pressure of all that mass creates a great crushing pressure. From this, as a buy product does come the heat. Insufficient mass to generate a fusion but, still a hot core... forever.

chornedsnorkack
2009-Dec-02, 10:10 AM
I do not think it would ever get cold. At some point the gravitational forces acting on the mass of the Earth... Deep within the core of Earth the pressure of all that mass creates a great crushing pressure. From this, as a buy product does come the heat. Insufficient mass to generate a fusion but, still a hot core... forever.

That is false. Pressure does not and can not generate heat. Matter at however high pressure and density can give away heat by conduction and cool to however low temperature.

But the cooling is slow. Inside Earth, the thin surface layer is solid, and gives away heat largely by conduction. The temperature rises to about 1000 Celsius in less than 100 km. At that temperature, rock softens so that it can convect - hot rock rises by its buoyancy, and cooler rock sinks by plastic flow.

Convection is a very much more efficient way of heat transfer, so in the remaining over 6000 km to Earth centre, the temperature rises to less than 6000 Celsius.

Moon is much colder, but not quite cold rock. From observations of moonquakes, the interior of Moon is hard and solid to the depth of perhaps 1000 km. From that depth, the deeper core seems to be soft, with temperature about 1000 Celsius. This soft core does mean that Moon will dissipate tidal forces such as free libration.

We have no idea what is inside other planets. No marsquakes seem to have been detected yet.

How long would it take for Earth to cool till Earth is as cold as Moon now?

Civilshock
2009-Dec-02, 07:54 PM
It appears you posted a question within an answer (while your answer did in fact help , I still want more)

You wrote:

"How long would it take for Earth to cool till Earth is as cold as Moon now?"

I would like to know how long it would take for the Earth to cool off to background temperatures (CMB Temp) given the "Hypothetical scenario" that the sun would live for Millions of Trillions of years or for the sake of the question, forever.

Planets must have some sort of cool down rate, which I would think would be correlated with the size (mass) of the stellar body in question. I have been told forever.....but nothing is forever and cool down is taking place albeit at a very slow rate.

How long would the earth have to live, if no other outside factors would effect its life, i.e. the Sun using up all its fuel.

antoniseb
2009-Dec-02, 08:34 PM
... I would like to know how long it would take for the Earth to cool off to background temperatures (CMB Temp) ...

If the Sun keeps radiating, the Earth will never get to CMB temps, however, if we change your question to something close, but a little more answerable:

If the Earth were moved into intergalactic space, how long would it take until the Earth's core was less than twice the CMB temperature?

This gets you past questions of being heated by local sources, and issues having to do with statistical mechanics, and the difference between exactly CMB v. undetectably warmer than CMB.

You are right to assume it will take a very long time. The rate of heat loss will go down as the amount of heat goes down.

Civilshock
2009-Dec-02, 08:54 PM
Thank you. Im new. :)