There are no articles any more that dream about the cities of tomorrow.

In the end, it's the people who are curious who change the world.

Three and a half million years ago our ancestors - yours and mine - left these traces [indicates footprints]. We stood up and parted ways from them. Once we were standing on two feet, our eyes were no longer fixated on the ground. Now, we were free to look up and wonder.

If each dead person became a ghost, there'd be more than 100 billion of them haunting us all. Creepy, but cool.

When you're a hammer (as the saying goes), all your problems look like nails. If you're a meteorite expert pondering the sudden extinction of boatloads of species, you'll want to say an impact did it. If you're an igneous petrologist, volcanoes did it. If you're into spaceborne bioclouds, an interstellar virus did it. If you're a hypernova expert, gamma rays did it.

Seventy percent of Earth's surface is water and over 99 percent is uninhabited, so you would expect nearly all impactors to hit either the ocean or desolate regions on Earth's surface. So why do movie meteors have such good aim?

Intelligent life can't be all that common because it's really rare on Earth and especially since we define ourselves to be intelligent. But in the eyes of an alien coming here who has the technology to make it here, they might observe us and conclude that there's no sign of intelligent life on Earth.