Can humans live on Earth a billion years from now?
Depends on your scenario - either way, almost certainly not.
Scenario 1: Humans live on Earth continuously from now for the next billion years. Given that our species is around 100,000 years old and a billion years is 10,000 times longer than that period, it's fairly safe to say that while our descendants (if clever enough to solve the problem in Scenario 2) could possibly still be alive, nothing identifiable as H. Sapiens will be around.
Based on our history, a few thousand generations is enough for speciation to occur in our particular ape species. A billion years is enough time for several million generations to occur! So humans could in principle be the common ancestors to thousands, if not millions of different descended species.
Define "live on earth"?
So as our Sun continues to age, it will do two things:
- Continue to output greater amounts of energy.
- Increase in size.
However, the timescales of these changes are pretty massive.
Referencing wikipedia: Sun - Wikipedia
Astrophysicists generally accept that the sun's energy output increases by about 10% every billion years or so.
So one billion years from now, the planet will be receiving 10% more energy from the sun.
Now, you may think to yourself: "Well, the average temperature of the Earth is about 57 degrees F, so that means it will only be up to about 65 on average, not too bad."
But this exposes a flaw in the thinking of many average folks: Our temperature scale is not absolute. 0 degrees does not mean 0 energy. If we convert the average temperature of our planet to Kelvins (where 0 K is Absolute Zero), it's 287 K. So increasing the temperature by 10% means an average global temperature of 315 K, or 107 degrees F.
That's a massive change. And that is only a very rough estimate that doesn't take into account how the increasing solar winds will begin to strip away our atmosphere. That means the planet will be less able to hold onto the energy it receives from the sun. That means the planet will experience higher temperatures in the daylight and much lower temperatures a night.
All in all, the planet Earth will be basically uninhabitable by then. However, the steady increase in the sun's output means that our neighbor Mars who is currently on the cold side will be a much warmer place, and may, in fact, be our primary residence by that point, assuming we haven't left our home solar system completely.
If our technology and understanding of the universe keeps progressing at the rate it is, or even a minute fraction of that, then "yes", we'd most likely be able to do anything we wanted. We could turn flowers into elephants with the click of a button, or a thought. We could transfer bodies at will, live as long as we wanted, move planets into any orbit we desire, create and destroy stars just for fun, and do anything.. really, anything.
Of course nobody really knows how humans are really going to progress.. I was just giving some extreme examples here, not to be taken too seriously. A billion years is a long, long, long, LONG, time, considering we went from swords and axes, to space, in a few hundred years.
Really, nobody can predict with any accuracy how we will evolve and how our tech and understanding will change. Anybody who gives a "definite" answer is full of crap. We could hit a point where it's just not possible to learn anything new, in a few hundred years; and just remain stagnant for the next billion, or we could discover FTL tomorrow, and populate the whole galaxy in 647 years..
Just came across this interesting Wiki page that describes our galaxy's timeline in "galactic years". It's definitely worth a quick look. Galactic year - Wikipedia
Humans are an incredibly adaptable species, and can manipulate our environment to suit our needs.
For this reason alone, I don't accept the arguments that global warming will drive humans to extinction. Even if it wipes out 99.99% of humanity, that would leave the better part of a million, easily more than enough gene pool to keep the species going.
So in a billion years, when the sun's energy output has increased by around 10% and the planet is uninhabitable, any remaining humans would have structures and bunkers with livable environments and wold extract the necessary resources to keep things going.
Some answers argue that since this timeframe would be thousands of times longer than our species has even existed, that humans would have long since evolved into something else, but there is absolutely no reason that should necessarily be so.
For one thing, humans have become very good at negating the diseases and defects that would otherwise kill people off and serve as selection factors. As "Darwin Awards" remind us, we even have laws and practices that help prevent dumb people from removing themselves from our gene pool.
And for another thing, humans are the authors of the taxonomy that define humans as human. So if humans change (evolve) drastically, they're still going to define themselves as human.
There are so many variables to such a question that it's really impossible to answer.
Humans, as we know them today, won't exist a billion years from now. Our descendants will have evolved into something that will likely be no more recognizable to us as single-cell life of a billion years ago would be to us.
We know that the Earth itself, all things being the same, won't be able to support present-day human life in a billion years. As the Sun ages, its luminosity increases. Scientists have estimated that within another 600 million years, it will have increased its energy output enough to set off a runaway greenhouse effect on Earth, with the tipping point likely at about that point. After a billion years, the Earth will be like Venus is today.
This could change, of course. Our descendants may have the technology to simply move the Earth to a wider orbit, staying in the solar habitable zone. Or we might just move to Mars, which will have Earthlike temperatures at that time. Or perhaps we'll just build whatever livable habitats we need.