So, back to the gedankenexperiment. Currently, a random meat probe dropped on the Earth's surface has something like a 15% chance of finding it survivable. But a random sampling over the historical epoch would return a survivability probability of around 1%. And over the future epoch, it's likely similar, unless we're erring massively on the side of pessimism about the prospects for our atmospheric composition remaining stable. Ergo: to a space probe searching for somewhere that our kind of life can thrive, a truly random sampling of the Earth's surface (distributed over both time and area) would probably result in the conclusion that the planet is uninhabitable. - Todd Suomela