"All life on Earth depends on the Sun for survival"

It’s been said before that all life on Earth ultimately depends on the Sun for survival, but would, say, some bacteria in undersea volcanic vents manage to get by, or would they just run out of organic matter to eat since everything else would die?
(Ignoring the gravity issue if the Sun disappeared and focusing only on the Sun’s light and warmth.)

It’s not true. There are organisms that rely on deep ocean thermal and chemical sources for life, and if the sun went out tomorrow, from what I’ve heard, they would live on for potentially billions of years without ever knowing the sun was ever there.

ETA: Stuff like this.

The more general term is ‘chemotroph’:


So apparently at least some don’t need sunlight at all.

NOAA has more information.

Then there are the tube worms:

From everything I can find, none of these species depend on sunlight directly or indirectly. They’d survive if we were orbiting a cold dark mass the same way as they do now, until the Earth itself had cooled sufficiently that none of the vulcanism they rely on was happening any longer.

There are also microorganisms living deep inside the earth. A quick Google is dominated by recent discoveries of bacteria just a few hundred meters under the ocean, but a paper from the nineties said they found them in rocks 1.7 miles deep in the continental crust.

Note that aerobic chemotrophs are indirectly dependent on sunlight because they require the oxygen that is produced by green plants. There are, however, some anaerobic chemotrophs.

Have any of the deep sea life forms mentioned here evolved from surface life forms? If so, then they were probably dependent on the sun at some point in their history, even if not now.

Probably not. In fact, it has been speculated thatlife itself originated in submarine volcanic vents. Some of the earliest life forms may have been chemosynthetic.

Just so no one is confused, Colibri is talking about the bacterial chemoautotrophs that form the bottom of the food chain in these vent communities. The multi-cellular animals like the worms and crustaceans all had ancestors from regular surface ecosystems. Even the vent tubeworms that never eat get their nutrition from symbiotic chemotrophic bacteria, they aren’t able to directly metabolize the vent chemicals.

The first bacterial life on earth was chemotrophic, photosynthesis didn’t evolve until a billion or two years later.

And just to add a little more, the chemoautotrophs living in rock deep down inside earth’s crust are not thought to be the origin of life.

I was about to post that speculation. I just want to add that it has to be one or the other. The existence of a unique genetic code virtually certainly implies that there is only one origin of all current life on earth. It might have been on the surface; it might have been in those deep vents; it could not have been both. Which is not to deny the possibility that life originated more than once, but only one of those origins has survived till today.

Things living deep inside the earth or at volcanic vents may not depend directly upon the sun, but one indirect result of the sun being there is that the earth stays at a temperature of about 300K. Take away the sun and that background temperature is going to plummet. When the seas start to freeze and the earth’s hot core starts to cool off faster than it did with the sun there, things will change. Perhaps life will be able to evolve rapidly enough so that it can still live with the ambient temperature lower than it had been (as in the science fiction short story Infra Draconis, where life survives in geologically active bodies without a nearby star (in the Magellanic Clouds). But it’s not a given.

Here’s a letter to Nature from David Stevenson about the possibility of internally-heated, life-supporting planets in deep space.
The Possibility of Life-Sustaining Planets in Interstellar Space

They think that there might be liquid oceans deep under the ice of several of Jupiter and Saturn’s moons. At a certain point the ice above will provide insulation for the deeper waters. As for the Earth’s core, from what I recall it’s not going to wind down for billions of years, so life could continue to exist over those thermal vents for a hell of a long time with or without the sun. In fact, it might actually last longer down there without the sun going all red giant on us than having the thing.

Another possible survivor would be radiotrophic fungi. They evolved from more conventional forms of life, but have developed the trick of getting the energy they need from gamma radiation.

HEY … peoples have melanin … did humans get left out of the evolution gravytrain again

There’s also Desulforudis audaxviator, a bacterium found deep in a mine in 2006. It survives on sulfate ions that are, in turn, produced from radioactive decay — no sunlight required.

Hey, humans doubled-down on a very specialized, but very successful, strategy: Have big brains and complex language and evolve by changing our cultures and making tools. It’s working rather well for us so far, compared to other great apes.