The Saga of the Chicxulub Crater

When the Alvarez team announced to the world that the K/T boundary clay contained a excess of iridium they suggested that it could only be explained if a comet or asteroid had slammed into the earth 65 million years ago. The iridium was deposited when a cloud of debris created by the vaporization of the object upon impact girdled the earth and fell back to form the so-called fireball layer. Most earth scientists were skeptical when they first heard about this.

If an object 10 kilometers across had collided with enough force to trigger a global environmental catastrophe that precipitated the extinction of more than half of the species alive at the time, where was the crater? It didn’t take crater experts long to figure that the scar left by such an impact should be huge hole in the ground about 180 kilometers across and a tenth as deep. If it existed, it shouldn’t be hard to find, unless it was under the ocean somewhere, or covered in vast amounts of sediment.

It turns out that when the search for the crater began there were several people, perhaps dozens, who already knew where it was. However, they either didn’t know that the search was on, or weren’t allowed to reveal what they knew. The saga of the discovery of the K/T impact crater beneath the north coast of the Yucatan Peninsula of Mexico began many decades before the discovery of iridium in the K/T boundary layer.

The saga goes all the way back to 1947 when a gravity survey was started in the Yucatan by the Mexican national oil company, PEMEX. Surface gravity measurements allow geophysicists to detect the structure of rock formations deep beneath the earth’s surface. The study of gravity maps of a region then helps the scientists to figure out where oil might be found; at least that is the goal.

The Yucatan survey turned up some intriguing data, including hints of a circular feature some 1,000 meters deep. In the early 1950s test wells were drilled, but no oil was found.