When will the Sun end all human life on Earth?
If nothing else wipes out human existence prior to this, at what point will the Sun make Earth uninhabitable for humans?
You're already assuming we don't destroy the Sun in the interim. It's a damn good source of raw materials.
@PatrickStevens Not all that good. It is mainly hydrogen and that isn't exactly rare. All those materials are very hot and at the bottom of a deep, deep gravity well. At the very least, we aren't going to be horning in on the sun until Jupiter is gone.
@corsiKa He covered that with, *"If nothing else wipes out human existence prior to this"*.
@Shane And we have of the order of a billion years to play with! Pretty sure we'll exhaust Jupiter in that time.
Relevant: Distant future of the Sun and Earth revisited and this answer to the question What will happen to life on Earth when the Andromeda and Milky Way galaxies collide? Notably: We only have 1, maybe 2, billion years before water boils off the surface, at which point I think we can make the claim that Earth no longer sustains life.
Are you assuming that "humans" will be the same then, in thousands of millions of years, as we are now, which we have only been for a few hundred thousand years?
The Sun is gradually getting larger and brighter. In fact, as called2voyage pointed out, its brightness is increasing by 1% every 100 million years. You can see how the Sun will change in the future from this graph: (Source)
According to this paper, within 1 billion (short scale) years from now, the ever-increasing luminosity will have made Earth nearly uninhabitable. The average temperature will have reached 47°C, compared to its current 15°C. Essentially no water will be left either, except at the poles. This may allow for simple life to survive for a while.
By 3.5 billion years, Earth will no longer resemble its current self. Its oceans, magnetic field and ozone layer and plate tectonics will be no more. Its surface temperature will skyrocket to roughly 1,330°C, hot enough to melt surface rock. No longer will our planet resemble a pale blue dot, and it will be more like Venus. Our planet is officially dead, along with all life on it. (Source)
~4.5 billion years from now, the Sun will become a red giant and possibly consume Earth. However, according to this paper, it may heat up potentially habitable bodies like Triton, to the point where they would support life. Unfortunately, the Sun won't remain in this stage for long enough — life usually takes billions of years to develop.
Great answer, although I'm not sure we can truthfully assert _"life usually takes billions of years to develop"_ when we've only "witnessed" it once.
@LightnessRacesinOrbit I agree. It is also unclear what form of life is being referred to.
@LightnessRacesinOrbit Considering it took billions of years for life to develop on Earth, we can safely rule out life appearing in the time the Sun is post-main sequence.
It also depends on what definition of "develop" you use, as the earliest evidence for life we have here shows that life was present within 400 million years after earth's formation.
Related to "life usually takes billions of years to develop". (1) development is the process by which one individual goes through the different stages of life (typically from a single cell to a grown up for multicellular lineages). The correct term is probably "originates" or "evolve" (but I am not sure what you meant exactly), no "develop" (2) Life took about 0.5 billions years to first appear on earth and much less time when you consider the existence of a range of 'putatively appropriate' conditions for life to originate. (3) Generalization from a single observation is likely misleading.
Off-topic: What caused that big dip in luminosity half a billion years after the sun started to shine?
@Shane I assume it's because that was when the Sun finished its contraction and became main-sequence. Before that point, the Sun was constantly losing energy as it shined. After it became main-sequence, nuclear fusion started producing much more energy.
Alright everyone. You heard the man. We've got 1 billion years before this thing is uninhabitable. Let's get moving, people!
While I'm nowhere close to an expert in simple life's biological development, I think Sir Cumference has a point, that even if it's a sample size of one, there's many steps between simple, first forms of life, and your basic, DNA based, photosynthetic with a nucleus. There's many more steps before you get multi celled, and after that, there's another long time before things like eyes and teeth, and a brain develop within that multi-cellular organism. It doesn't happen quickly, but once life get eyes, teeth, a brain and competition, then it things can progress fairly fast. (IMHO).
@userLTK It's really hard to tell with the tiny sample size. For example, a lot of the "leaps" in complexity happened during (or after) a catastrophe of some kind. It might very well be that life on another planet might have been luckier and got their catastrophes earlier (if there is any causal connection in the first place, of course). We don't know how many kinds of life have existed in the past - we only have a very spotty record and a lot of indirect evidence. Heck, it's possible (though unlikely) that there was intelligent life on Earth before us and we just didn't find any record yet.
@userLTK And we have plenty of evidence that when the evolutionary pressure is high, the "development" can get very fast indeed - while when food is abundant and there's not a lot of competition, it can stagnate for hundreds of millions of years. You also get stagnation when things get *too* harsh. There's so many unknowns and variables that we just can't tell - it's not like there's a physical law that prevents an advanced form of life from developing within a hundred million years; we just don't have any evidence that it did on Earth in the past.
@Luaan I'm not an expert in such things, and I'm not sure anyone is, since we didn't see it happen and there's only fossil records, but there's an enormous variation in one celled life and many steps that need to take place just to get the first bug, or, the first plant. I remain skeptical that it can happen "quickly". There may be no physical law, but there may be a practical limit of at least a few hundred million years for first-early life to become complex, animals, fish and plants (IMHO). I do agree with you that there are significant unknowns.