Who killed the Dinosaurs 65 million years ago?
Friday, March 31, 2006 1:37:35 PM
As cosmic matter has higher iridium concentrations than terrestrial materials Alvarez concluded that the iridium was due to a large meteoritic impact 65 million years ago. In other parts of the world high iridium concentrations were found at the K-T boundary as well. It took some time however to find a suitable impact crater – the now world famous Chicxulub crater.
For about 20 years most of us have been happy to believe that the Chicxulub event killed the Dinosaurs (or at least I have).
On Monday 3 April 2006 a paper will be presented at the Backbone of the America conference that raises some doubt.
Some of the rocks that melted at the impact were ejected far from the crater as glass spherules (this is normal and such glass spherules are often used as indicators of an extraterrestrial impact). A careful geochemical fingerprinting of glass spherules found in multiple layers of sediments from northeast Mexico, Texas, Guatemala, Belize, and Haiti all point back to Chicxulub as their source. But the analysis places the impact at about 300,000 years before the infamous extinctions marking the K-T boundary.
Disconnecting the Chicxulub impact from the K-T boundary would make sense of some other oddities in the iridium layer. In the Gulf of Mexico, close to the impact site, iridium is found at a weak concentration, just one part per billion. Yet farther away in Denmark, higher concentrations of iridium are found.
If not the Chicxulub event – what then created the worldwide iridium layer?
See also my blog on Deccan Traps and Dinosaur Extinction.