By preventing dangerous asteroid strikes, we can save millions of people, or even our entire species. And, as human beings, we can take responsibility for preserving this amazing evolutionary experiment of which we and all life on Earth are a part.

Asteroids have hit the Earth millions of times. We can see them as shooting stars every night. When they get bigger, things get complicated. It is only a matter of time until a big one hits us. And since we can do something about it, we should.

An asteroid can literally destroy 80 or 90 percent of the species that are alive on Earth. These are big events. I mean, this is called extinction.

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.

You see the Earth as a bright blue and white Christmas tree ornament in the black sky. It's so small and so fragile - you realize that on that small spot is everything that means everything to you; all of history and art and death and birth and love.

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