Um. Yeah. What the title says. Why is the earth’s core so much hotter than the crust. Rock is a pretty good insulator, sure, but that doesn’t mean it won’t eventually heat up if you heat it for long enough. So what gives?
First:
I gotta get ahold of that search engine. But back to the OP:
Don’t forget that outter space is pretty damned cold. The core might be a self-perpetuating furnace, but there’s a cold side too.
Tripler
It’s like a McBLT: Hot on the hot side, cool on the cool side. And oh-so-good in the middle.
I don’t think outer space is cold, it’s a vacuum.
Besides, we have heat coming in from the sun. That balances the exchange, doesn’t it?
Just to expand on what Flying Ramen Monster said (Infidel! How dare you take His Noodly Goodness’s name in vain)… when the Earth formed it was all pretty damn hot. But the Earth is in space which is pretty damn cold. So the Earth cooled.
(And then the dinosaurs came…)
So the Earth has been cooling ever since. But the shell cools first cos it’s exposed to space. The heat is gradually conducted outwards, from the core to the outer core to the mantle to the crust, to the atmosphere, to space. So the Earth’s core DOES heat up the rest of the Earth, but the rest of the Earth radiates the heat out into space. The ‘steady-state’ heat distribution is hot in the middle and cooler going out.
As an aside, if there were no mechanism for heat production inside the Earth, then it would have cooled much quicker than it has done. So back in the day, prominent physicists like Kelvin couldn’t accept Darwin’s theory of evolution, as they could only imagine the Earth was (something like) 60000 years old (given how hot it still was), and this wasn’t enough time for evolution to occur. Then people discovered radioactivity, and that the Earth’s rocks were substantially radioactive, and this produces heat, which keeps the Earth hot.
There ya go!
:smack: I meant to expand on what Tripler said. And I put extraneous spaces in FlyingRamenMonster 's name. But it’s yer own damn fault for being an apostate.
Triple post, woo-hoo!
Outer space IS cold. It’s -270 degrees C, or three degrees above absolute zero.
(You might then ask, how can a vacuum have a temperature? Well firstly space isn’t a complete vacuum, it does have some dust particles in it, and as long as it has particles, you can calculate their average thermal energy. But secondly, even if it was a perfect vacuum, you can still assign a thermodynamic temperature to it. Stick a very cold body into it. If that body does not lose heat, then the vacuum is the same temperature as the body. Oh I forgot photons. Even a vacuum with no material particles in it [electrons, protons, neutrons] still has light particles whizzing through it . They have well defined energies, and therefore the space has a well defined temperature)
And the heat coming from the sun wouldn’t balance out the heat coming from the Earth’s core. The sun’s very far away and the heat the Earth gets from it is small compared to the heat coming up from underneath.
While your information about space being cold is correct, you are wrong on the sun vs earth contribution to our temperature. For the continental US, the sun provides on the order of 5 kwh/m^2/day (July US solar data.) The heat flowing from the center of the earth to the surface is on the order of 100 mw/m^2 (Heat transfer from core.)
If we convert the units of the first number to match the units of the second, we get 208,000 mw/m^2 from solar gain vs 100 mw/m^2 from the center of the earth. So for surface temp, the energy from the sun is far more important than energy from the earth’s core.
But while we get this heat from the sun every day, we lose a like amount every day through radiative heat loss to the cold rocks and dust specs floating around the galaxy.
Wow! I stand corrected on the Earth v Sun bit. Thanks Boringdad !
(And now I :smack: myself for not realising that the difference in climate between the Antarctic and the Gobi Desert might just mean the Sun’s contribution to surface temperature is kinda important after all…)