We have converted huge swaths of land and ocean into human habitats where we live and grow food and harvest energy. But there's been a sea change in the past century.

I would want us to start our quest to survive mass extinction by rethinking how we build cities. Cities should be commonplaces of production, rather than consumption - they should be producing food, and fuel.

The fact that we have been able to perturb the carbon cycle with our industrial revolution is evidence of how vulnerable we are - because when we destroy our environments, we destroy our food and energy supplies. In short, we destroy ourselves.

I think small animals can escape from many kinds of natural disaster more easily. There are just more places for them to hide, and more ways for them to find safe habitats. So this means that rats are set up to rule the Earth, but most of us already knew that. Now you know why.

In fact, the early demographer Thomas Malthus believes that the only way the human population would ever check itself was by running headlong into a disaster, like a pandemic or famine. Sometimes we get so frustrated with the slowness of human political processes that we wish a giant flaming rock would solve the problem for us.

Imagining the world without us is a recipe for despair and paralysis. I actually think it's more helpful to imagine the world before us, to look back at those unstable ecosystems of the Triassic and realize that were in another phase of unstable ecosystems. Knowing that, demystifying our situation as it were, makes it easier to think about solutions. We are not looking into the unknown. The only thing unknown about the situation is how we're going to fix it, and when.

Even though I now know that it's likely the Earth will suffer through mega-volcanoes or meteor strikes that could take out millions or billions of people, I feel less anxious about it because I actually understand what the threats are. There's nothing like researching something exhaustively to make it less terrifying.