What are the main heat sources for Earth's equilibrium surface temperature?

[Loren Booda]

What would Earth's equilibrium surface temperature range be from

1. Internal fission alone

2. Gravitational tidal forces alone

3. Solar radiation alone

 

[cesiumfrog]

I suspect current surface temperature is basically a result of solar radiation combined with atmospheric effects. But below the surface crust, why hasn't the Earth solidified yet?

 

[mgb_phys]

The surface temperature is pretty much in equilibrium with solar radiation.
The core was remelted about 0.5Gyr after the Earth formed due to internal radioactive decay ( not fission ).
There is some tidal heating of the core but it is negligible.
It hasn't solidified because there is quite a lot of it, the crust is not a good conductor and the surface+atmosphere are at 300K.

 

[cesiumfrog]

Remelted? How do we know it was solid?

 

[Chronos]

Radiative transfer from the core to the surface of the Earth is extremely inefficient. The Earth's crust is a superb insulator.

 

[mgb_phys]

Remelted? How do we know it was solid?

The original gas, dust and small rocks that formed the Earth were solid. They were small and exposed to the cold of space. They would have melted and flowed under gravitational pressure as the Earth grew that's why the Earth is spherical while asteroids and small moons are more 'lumpy'.
I'm not sure that the Earth necessarily cooled into a complete solid before the heat input from radiation melted it again. Certainly the mantle and crust were 're'-melted but it might be that the core never solidified - sorry not quite my field.

The dates come from a combinatiopn of cooling rates, estimates of the total amount of radiation from level sof decay products and the dates of the oldest rocks found.

 

[cbacba]

the remelt was just a bit of the surface. What's more, I subscribe to the mainstream notion that the moon was formed when a Mars sized planetoid came smashing into the earth. That was enough kinetic energy to turn the place into a major molton disaster.