A new study of melted rock ejected far from the Yucatan's Chicxulub impact crater bolsters the idea that the famed impact was too early to have caused the mass extinction that killed the dinosaurs 65 million years ago.From the GSA press release:
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 that mark the boundary between the Cretaceous and Tertiary periods, a.k.a. the K-T boundary.
Using an array of electron microscopy techniques, Markus Harting of the University of Utrecht in the Netherlands has found that chemical compositions of the spherules all match what would be expected of rocks melted at the Chicxulub impact. The spherules are now found in several layers because after they originally hit the ground, they were "reworked" by erosion to create later layers of sediments, he said.
Above these, and younger still, Harting has also identified the famous layer of extraterrestrial iridium in sediments worldwide which was originally touted as the smoking gun for an impact somewhere on Earth at the K-T boundary.
Harting is scheduled to present his latest findings on Monday, 3 April Backbone of the Americas-Patagonia to Alaska. The meeting is co-convened by the Geological Society of America and the Asociación Geológica Argentina, with collaboration of the Sociedad Geológica de Chile. The meeting takes place 3-7 April in Mendoza, Argentina.
The sediments from the region are also providing clues to what transpired during those 300,000 years between the impact and the K-T boundary die-offs. "Nothing happened between them," said Harting. "The K-T iridium layer is a totally different event."
Disconnecting the Chicxulub impact from the K-T boundary also helps 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, says Harting. Yet farther away in Denmark, higher concentrations of iridium are found. "This doesn’t really make sense," he said, unless, of course, the impact and iridium layer are not related.
All this begs the question: What, then, created the worldwide iridium layer, if not a humongous impact? One possibility is that Earth and perhaps the entire solar system was passing through a thick cloud of cosmic dust 65 million years ago.
"You probably have a time when lots of meteorites are coming down and never touching the ground," said Harting. Instead they burned up as "shooting stars," depositing their iridium in the atmosphere. There it was quickly rained out, washed into lakes and oceans and buried in contemporary sediments.
Crater from HERE.