In one billion years the Sun will get so bright that all the oceans will evaporate but it’s unlikely that human life will even make it that far. A typical mammalian species lasts a million years, if you don’t include mass extinction events like the one wiped out the dinosaurs 66 million years ago.
There is a one-in-a-million chance of asteroid impact causing humanity’s extinction in the next century, and volcanic eruptions big enough to cause catastrophic climate change occur about once every 50,000 years. An ice age is also inevitable. These tend to happen every 40,000–100,000 years and we are long overdue one. Humans survived the last ice age, but modern civilisation and infrastructure almost certainly won’t.
A large pandemic involving one or more viruses, or antibiotic-resistant bacteria, might see the population reduced to small, scattered groups, but no infectious disease in history has come close to wiping out the entire human race.
The largest danger we face is ourselves. We have developed a huge number of methods to protect ourselves against natural disaster; the irony of being such an advanced species is that we have also vastly increased our ability to self-annihilate. Modern estimates give us a 1 in 5 chance of wiping ourselves off the planet in the next century.
Self-replicating nano-bots have the potential to consume all matter on Earth to build more of themselves. Superintelligent computers might turn all the matter in the solar system into a giant calculating device to solve a mathematical problem. More than ever, we are stepping into a dangerous scientific unknown.
And the situation if we don’t survive? In 10 years buildings will have begun to disintegrate, and in 50 more fish stocks will recover, coral reefs regenerate and elephant populations grow 20-fold. 500 years in and forests will have returned to the state they were in 10,000 years ago. Carbon dioxide levels take 100,000 years to return to pre-industrial revolution levels. In a few billion years, our legacy to the universe is what has been sent to the moon and rocketed into deep space. And then the sun will explode.