As you pass from sunlight into darkness and back again every hour and a half, you become startlingly aware how artificial are thousands of boundaries we've created to separate and define. And for the first time in your life you feel in your gut the precious unity of the Earth and all the living things it supports.

We could not wipe ourselves out with a nuclear war. I do not want so sound too positive. It would be a catastrophe, but it would not be a final one. We are not powerful enough for that. An asteroid could be that powerful. That is why we need to do our homework.

It would take an extremely large spacecraft to deflect a large asteroid that would be headed directly for the Earth.

It is not enough to do a desktop exercise of a Beethoven symphony. You need to practice with an orchestra. The musicians need to read the notes. Otherwise it will be a disaster.

I am interested in climate change and other topics too. But this thing is so huge, in the worst case we are talking about the end of our civilization.

We can both prevent asteroid impacts and address climate change. It's not either-or.

If we do our homework right, never again should an asteroid that can do damage on the ground impact the Earth. We're living in a time-with our technology-we have the capability to eliminate that major shaper of evolution . . . the evolution of life on this planet.