
“Although the chance of a disaster to planet Earth in a given year might be quite low, it adds up over time, and becomes a near certainty in the next thousand or ten thousand years.
“By that time, we should have spread out into space, and to other stars, so a disaster on Earth would not mean the end of the human race.
“However, we will not establish self-sustaining colonies in space for at least the next hundred years, so we have to be very careful in this period.”