|Photo Courtesy of NASA|
Scientists have found new evidence supporting the hotly contested theory that a comet collision was responsible for a North American extinction at the end of the Pleistocene approximately 12,900 years ago. The impact is said to have wiped out the Clovis, a Paleoindian culture thought to be the continent’s first human inhabitants, and 35 mammal and 19 bird species.
A team from the University of Oregon has reported shock-synthesized hexagonal diamonds in 12,900-year-old sediments on the Northern Channel Islands off the southern California coast. The tiny diamond and diamond clusters were also found in association with soot, whose presence in the sedimentary record indicates extremely hot wildfires.
Scientists point to the geological similarity of the proposed California impact site to the Chicxulub crater in Mexico, the site of an asteroid collision 65 million years ago that wiped out the dinosaurs (although this theory still has its critics as well). The Chicxulub crater has a thin iridium-rich layer also containing shocked quartz. The hexagonal, crystalline structure of shocked minerals is only formed under extremely high temperatures and pressures, two conditions consistent with a cosmic impact.
The age of the impact sediments corresponds with the extinction of the pygmy mammoth on the Northern Channel Islands, camel, horse (later reintroduced on the continent by Europeans) and approximately fifty other bird and mammal species. The timing of the extinction also matches the beginning of the Younger Dryas, a period of abrupt climate change nicknamed the “Big Freeze” that impacted Europe, North America and as far south as New Zealand. The University of Oregon team argues the abrupt Younger Dryas climate change happened as a result of several comet strikes dispersed across North America; the southern California site the first to be discovered.
The paper appeared online July 20th ahead of print publication in the Proceedings of the National Academy of Sciences. Other theories argue overhunting by Clovis populations caused the rapid extinction of large mammals around the end of the Pleistocene. But many researchers are hopeful the discovery of the shocked minerals in the Northern Channel Islands will be the smoking gun for the comet theory.
|Map of the Northern Channel Islands where the hexagonal diamonds were discovered in 12,900-year-old sediments. Photo courtesy of NOAA and UC Santa Barbara|