I'd written a book about astrobiology, which is the hunt for life beyond Earth, and that was what led me to this to some extent. One of the things brought home is how we need to think in astronomical time, where a billion years is nothing.
And the amazing thing about Mars is that it has changed much less than the Earth has, where human life has changed everything. Conditions are similar to what they were four billion years ago. So it's quite possible that one day scientists will be able to say: "We've detected remnants that tell us there was once biology here." It's very hard. It requires both the instruments and a leap of the imagination.
So if things continue, if more missions go and more nations get involved, I think it's quite possible they'll discover that there once was life on Mars. And that would be one of those moments, like when Copernicus said the Earth isn't the center of the universe. It changes everything. Because if there was a genesis of life on Earth, and also a separate genesis of life on Mars, it means that it's almost impossible that there aren't a lot of other planets where there's life. We might not be able to see it at any given moment, because astronomical time is so vast. But it would suggest very, very strongly that there's life out there.
