Scientific facts are often described in textbooks as if they just sort of exist, like nickels someone picked up on the street. But science at the cutting edge, conducted by sharp minds probing deep into nature, is not about self-evident facts. It is about mystery and not knowing. It is about taking huge risks.

I happen to love science... Scientists are all slightly mad. There is truth in the stereotype of the mad scientist. They are mad with curiosity.

No one knows exactly when or where the redwood entered the history of life on earth, though it is an ancient kind of tree and has come down to our world as an inheritance out of deep time.

We're creating these massive urban areas in the Third World. It's like you take the entire population of California and put it in one city. Then you remove basic sanitation and medical services, and you have a ticking biological time bomb.

Experiments suggest that if one particle of Ebola enters a person's bloodstream, it can cause a fatal infection. This may explain why many of the medical workers who came down with Ebola couldn't remember making any mistakes that might have exposed them.

If a vaccine works, then the vaccinators might conceivably set up what's known as ring vaccinations around Ebola hot spots. In this technique, medical workers simply vaccinate everybody in a ring, miles deep, around a focus of a virus.

Redwood time moves at a more stately pace than human time. To us, when we look at a redwood tree, it seems to be motionless and still, and yet redwoods are constantly in motion, moving upward into space, articulating themselves and filling redwood space over redwood time, over thousands of years.