Double Whammy: Dinosaurs made extinct by two impacts

The leading theory behind the extinction of the dinosaurs approximately 65 million years ago has been the massive impact of an asteroid in the Gulf of Mexico known as the Chicxulub impact. New evidence has just come to light that a second impact in Ukraine may have also been involved-prompting scientists to further wonder if in fact the Earth was subject to a wide-ranging meteor shower.

Using the 'double whammy' to understand the extinction of the dinosaurs

When the asteroid impact theory was first proposed in 1980, it proved hugely controversial. The discovery of the Chicxulub impact crater was the ‘smoking gun’ needed to cement the theory as the most plausible to date.

The new crater in the Ukraine - named the Boltysh Crater - is actually not all that new, as it was first reported in 2002. What is> new is that the impact event closely coincides with the timing of the Chicxulub event.

Examining the fossil record in the site, scientists have found two layers of mud which filled in the crater that have unusually high amounts of fern spores. Because ferns have an amazing ability to bounce back after catastrophic events (not only asteroid impacts, but lesser things like volcano eruptions), these ‘fern spikes’ are considered good markers of such events in the fossil record.

The discovery of one ‘fern spike’ layer would not necessarily meaningful, but in the case of Boltysh’s excavation, scientists found two spikes layered one metre apart. This suggests two large global events several thousand years apart. Professor Simon Kelley of the Open University, co-author on the study, said: "We interpret this second layer as the aftermath of the Chicxulub impact."

Some might say that two impacts several thousand years apart might not be the ‘double whammy’ reported in the headlines, but Kelley continued: "It is quite possible that in the future we will find evidence for more impact events." In fact, rather than ascribing the extinction event to one massive impact, it seems more plausible that the Earth was in fact victim to a meteorite shower that lasted several thousand years.