From my column in the November issue of Madison Magazine:

In the hills of far western Wisconsin, there is a hole that, when first made, was four miles across and three quarters of a mile deep. It is called, in a somewhat understated way, the “Rock Elm Disturbance,” and it was made by a giant rock that hit the ground from outer space.

I drove there because I wanted to see an impact crater with my own eyes. It was something I’d wanted to do since a few years ago, when I was happily reading along in Bill Bryson’s witty and informative book, A Short History of Nearly Everything, when I came across some startling facts.

According to Bryson, some “two thousand asteroids big enough to imperil civilization regularly cross our orbit,” and as many as “millions” of smaller ones—big enough to destroy a city—do, too. The number of known “near-earth asteroids” has gone from ninety-seven in 1980 to 6,384 today. [updated numbers here] The first planet killer wasn’t even spotted until 1991, and near misses are thought to happen as many as two or three times a week.

Read the rest here.