What Killed the Dinos? Part 2: Hunt for the Crater

In science, radical ideas are not welcomed immediately, writes Lisa Randall in Dark Matter and the Dinosaurs. A meteorite hit was such an idea. So scientists wondered if the iridium spike was caused by the volcanic eruptions in the Deccan traps? Did volcanoes bring iridium up from the bowels of the earth?

“(The traps are) bigger than half a million square kilometers (as big as France) and they are about two kilometers thick. That’s a lot of lava.”

Then the meteorite theory really began to gain favour, bit by bit:

-          The iridium spike was proving to be global, not regional to a few places. That much iridium only seemed to fit a meteorite as the source.

-          Next came the discovery of “shocked quartz” in the same layer across the world. Volcanoes didn’t generate that much heat. It did align with “impact melts” though.

-          Much later glass was found in the same K-T layer. It ruled out any gradual process since glass only forms during quick cooling. Like an impact.

Hmmm… but finding the crater corresponding to the impact would be conclusive. Could it be found? Or had it been eroded? Or was it lieing underwater, beyond reach? In fact, it had already been found in in the 1950’s, by industrial geologists working for an oil company named Pemtex! Of course, they didn’t know what they had found. Nor were oil companies going to share their exploration data. Finally though in 1978, Pemtex relented and the information was released. But it was too early (the meteorite theory was still in its early days), and nobody paid much attention.

In fact, the search for the crater went the opposite route, via deduction! If the impact had happened in the sea, but close to shore, reasoned one group, then the tsunami that followed would have left a telltale sediment deposit layer in nearby areas. Checks for such a sediment deposit suggested an impact site in the Caribbean/Gulf of Mexico/western Atlantic region. Another group found the largest shocked quartz deposit to be in the western parts of the US. A similar finding in Haiti indicated the impact site to be somewhere close. The crater position was getting narrowed down.

And now scientists realized that the Pemtex crater matched the expected position! They renamed it based on a nearby fishing harbor, a very hard to pronounce name: Chicxulub. On the other hand, the name meant the devil’s tail, which aligned with the name Alvarez had given it in anticipation as the “crater of doom”. Satellite imaging soon showed the crater’s circumference to be along expected lines: a whopping 80 km in radius. Glass discovered in the crater suggested a fast cause. Like an impact.

It was now official: a meteorite had indeed struck earth and it explained the iridium spike.