Washington:
Archaeologists have debunked the cosmic-impact theory that a comet sparked climate change at the end of the Ice Age, causing mass animal extinction.
According to the study, led by archaeologist David Meltzer from Southern Methodist University in Dallas, Texas, nearly all sediment layers purported to be from the Ice Age at 29 sites in North America and on three other continents are actually either much younger or much older.
Meltzer and his co-authors found that only three of 29 sites commonly referenced to support the cosmic-impact theory actually date to the window of time for the Ice Age.
"The supposed impact markers are undated or significantly older or younger than 12,800 years ago. Either there were many more impacts than supposed, including one as recently as five centuries ago, or, far more likely, these are not extraterrestrial impact markers," Meltzer noted.
Scientists agree that the brief episode at the end of the Ice Age - officially known as the Younger Dryas for a flower that flourished at that time - sparked widespread cooling of the earth 12,800 years ago and that this cool period lasted for 1,000 years.
But theories about the cause of this abrupt climate change are numerous.
They range from changes in ocean circulation patterns caused by glacial meltwater entering the ocean to the cosmic-impact theory.
Meltzer and his colleagues sorted the 29 sites by the availability of radiometric or numeric ages and then the type of age control, if available, and whether the age control is secure.
The researchers found that three sites lack absolute age control.
"The remaining 26 sites have radiometric or other potential numeric ages, but only three date to the Younger Dryas boundary layer," Meltzer added.
The findings were reported in the journal Proceedings of the National Academy of Sciences.