Cornfields -- which occupy a big fraction of U.S. farmland -- differ from normal ecosystems in that they are nearly sterile ecologically. Breeding and spraying aim to prevent anything from living but corn.
"We'll start in a cornfield — we'll call it an Iowa cornfield in late summer — on a beautiful day. The corn is high. The air is shimmering. There's just one thing missing — and it's a big thing...
...a very big thing, but I won't tell you what, not yet.
Instead, let's take a detour. We'll be back to the cornfield in a minute, but just to make things interesting, I'm going to leap halfway around the world to a public park near Cape Town, South Africa, where you will notice a cube, a metal cube, lying there in the grass."