Why is earth still so hot?

[Inquisitor]

Why is earth still so hot?

 

According to scientists, Earth is about 4000 million years old ball.

 

If this is true, and I'm sure it is, then WHY is the Earth still so hot???

 

I mean Earth only has a very thin crust of cooled down matter, and below this, there is molten magma that is really, really hot.

 

Why is the crust not thicker? Why has the earth not cooled down completely, to a ball of solid rock??? What has kept the Earth's innards so hot all these millions of years??? Why has not the very cold ice ages quickened the cooling down process??? Is it the warming presence of the sun or something???

 

Please help! I'm deeply puzzled!

[insane_alien]

appart from the radioactive decay of elements within the earth, the answer is that it hasn't had enough time. there isn't ver much thermal conductivity going on so only a trickle(relatively, its in the TW range iirc) of energy is being radiated from the earth.

 

thing of it like trying to empty the hoover dam by removing a single drop of water every year

[J.C.MacSwell]

1. Solar radiation

2. Radioactive decay

3. Initial Heat lost at current rate

 

Not sure if I have them in the right order for the present conditions.

[CaptainPanic]

In addition to the points made above (that I believe to be true, but I'm not an expert):

It may also be a heat-transfer limitation.

 

The atmosphere + 30 km of the earth's crust are pretty good at keeping the heat inside.

[SH3RL0CK]

I would think that at least a small amount of heat is added by tidal forces caused by the sun and moon as well.

[Sisyphus]

I have a thermos that can keep coffee hot for 24 hours. If you consider the Earth's properties as a thermos, it doesn't seem all that surprising. A vast nuclear reactor surrounded by molten and compressed solid rock twenty times as hot as my coffee, with a volume to surface area ratio millions of times as high (volume increases with cube of radius, surface area with square), surrounded by 20 mile thick skin of solid rock, surrounded by a solar-heated atmosphere, surrounded by vacuum. Not really surprising that we're talking about a timeline of billions of years.

[J.C.MacSwell]

I have a thermos that can keep coffee hot for 24 hours. If you consider the Earth's properties as a thermos, it doesn't seem all that surprising. A vast nuclear reactor surrounded by molten and compressed solid rock twenty times as hot as my coffee, with a volume to surface area ratio millions of times as high (volume increases with cube of radius, surface area with square), surrounded by 20 mile thick skin of solid rock, surrounded by a solar-heated atmosphere, surrounded by vacuum. Not really surprising that we're talking about a timeline of billions of years.

 

Cue the four Yorkshiremen from Monty Python:

 

"U'm amazed it's cooled as much as it 'as. Thought it would be tough living with all the heat."

 

"Never thought it would 'ave cooled enough to have evolved as far as we 'ave. Thought it would 'ave been still too bloody hot."

 

"Didn't 'spect to even start evolving at all...yet"...Not even an amoeba would try to survive at the temperature I expected it would be."

 

"What I meant by "living" was more like a pre-amoeba stage. I thought I might be that, perhaps living out on some trans Neptunian object. I certainly didn't 'spect to be evolving anywhere close to Earth."

 

"I expected to be singed to death on my trans Neptunian object...'alf an 'our before I even tried to form some DNA."...

[swansont]

Oh, trans-Neptunian objects. Luxury.

[J.C.MacSwell]

Oh, trans-Neptunian objects. Luxury.

 

Well when I said object I meant a Black Hole orbited by a piece of tarpaulin.

 

It was an "object" to us.