Humanity is at risk from a series of dangers of our own making, according to Prof Stephen Hawking.
Nuclear war, global warming and genetically-engineered viruses are among the scenarios he singles out.
And he says that further progress in science and technology will create “new ways things can go wrong”.
Prof Hawking is giving this year’s BBC Reith Lectures, which explore research into black holes, and his warning came in answer to audience questions.
He says that assuming humanity eventually establishes colonies on other worlds, it will be able to survive.
“Although the chance of a disaster to planet Earth in a given year may be quite low, it adds up over time, and becomes a near certainty in the next thousand or ten thousand years.