Without the Sun Would All Life on Earth Really End?

It’s a frequently stated fact that without the sun (meaning the light and heat from the sun*) all life on Earth would end.

But I wonder, would it really?

I tried Googling it. Apparently the surface of the Earth would eventually end up at -400F.

But would that end all life on Earth?

We know that tardigrades can already survive at that temperature. Wouldn’t other microscopic life evolve to be able to survive?

There are moons with liquid oceans in the solar system. They’re not dependent upon the Sun to maintain those liquid oceans. So would the Earth’s oceans really freeze solid? Or would some of the ocean stay permanently liquid? Yes, the heat from the Earth’s core would eventually be lost to space, but would the parts of the ocean nearest to the source of heat receive enough heat to stay liquid?

And even if the oceans did freeze solid, wouldn’t volcanic action periodically melt sections of the ocean? Kind of like desert life that only emerges when it rains, would the ice contain dormant life that would activate if the ice it was in melted?
*I’m specifically not saying the sun suddenly disappears or something like that as I know we’re dependent upon the mass of the sun for its gravitational effects.

I suspect that life would continue around volcanic vents, where there is a temperature difference that can be exploited to provide energy for life. The idea of a world where internal volcanism provides the energy for life has appeared in science fiction stories. See, for instance, Georgy Gurevich’s 1958 novella Infra Draconis.

Life away from heat sources can continue for some time, but as life recedes further from the sun, or more time passes since the sun went away, it’s going to get harder and harder to find the energy input needed to sustain life, and things will die, or go into perpetual hibernation. Barring such weirdness as superconducting creatures 9which seem as if they ought to violate conservation rules), you’ll need some input. Fritz Leiber’s 1951 story A Pail of Air imagines people living in colonies around nuclear reactors underground after the earth is torn away from the sun in a catastrophic event.

It’s not true that all life on Earth depends on sunlight (although most of it does). There are many chemosynthetic microbes that obtain energy from splitting chemical compounds, and other organisms that feed on them. Life will continue as long as such compounds remain, and as long as enough heat is available from tectonic forces, residual heat from the Earth’s formation, and radioactivity to keep water liquid.


This 1998 letter by David Stevenson to Nature shows some estimates ofd this possibility; basically life in deep space is a possibility, and may even be the most common location for life in this universe.

But it seems unlikely that life of this sort can evolve into tool-using species, and these planets are so isolated that we would be hard-pushed to find them in the dark depths of space.

Reminds me of A C Clarke’s short story Crusade

I would be interested to know, if the sun didn’t exist, what temperature would the earths oceans be at due to tidal forces from the moon? I am guessing that there would possibly still be a liquid ocean under a frozen surface even if the sun didn’t exist.

Also…the further underground you go, the hotter it gets. That’s not from the sun.

So even if the Earth’s surface temperature is -400F, deep underground it should stay warm enough for liquid water. So shouldn’t there be life at those temperatures?

The problem comes if the oceans mostly freeze solid. If the only liquid water is around the vents, then how do new vents get colonized? As old vents close and new vents open the vent colonies are going to get simpler and simpler as species don’t make it to the new vents. And eventually the last vent that supported life goes dark and the new vents are sterile, and the last bit of life on Earth is gone.

But if the oceans don’t freeze solid then there’s a lot more opportunity for life forms to move around and the situation isn’t quite so precarious.

There have been a few thread here that asked a variation along the lines of “how long could humans live if the sun went away” sorta thing.

Maybe somebody here that is more skilled/less lazy could link them.

There is life down there and it would presumably remain until the entropy death of the earth, when all radioactives have decayed and the tectonic plates quieten down. But there really doesn’t seem to be much chance of developing any kind of multicelluar life and higher organisms.