Death by asteroid

(Webster's World Encyclopedia, July 1997)

"The asteroid that wiped out the dinosaurs" is now widely accepted by scientists, but how many other extinction events were caused in similar ways? Siberia, home of the Tunguska event, is also the home of the Popigai impact structure on the Anabar shield. Popigai is a remnant of a huge crater, 100 km across. The crater was formed some time between 5 and 65 million years ago, although it was probably older than 29 million years. Nobody could be more precise than that, until age determinations were carried out using argon isotope ratios.

Now the impact is dated at about 35.7 plus or minus 0.2 million years ago, almost the same time as the Chesapeake Bay crater off the coast of North America, and raising the interesting question that the two impacts may have been two parts of the same object, and suggesting that the impacts may have caused the mass extinction of the late Eocene.

We now know that northern Italy has an iridium anomaly and shocked quartz in Late Eocene deposits, and the dating for these finds is consistent with the Popigai dates. This age is also similar to that of the North American tektites, which have been associated with the Chesapeake Bay impact structure in the eastern United States, making it even more likely that the events were close together, and part of something big.