Scientists are dismissing a popular theory about mass extinction since the last ice age. The Younger Dryas Impact Hypothesis contends an asteroid hit Earth 13,000 years ago changing the climate instantly and dramatically. Scott Anderson, a paleoecologist at Northern Arizona University, is part of an international research team that looked for evidence to support this explanation, but didn't find any.
"If you can imagine an asteroid hitting the earth, there would be lots of almost instantaneous environmental change. And so, one has to look for changes in the environment that happened contemporaneously with that impact. And when we do that, we find that we cannot confirm changes that the original proposers of the hypothesis suggested," Anderson says.
Anderson searched for clues on Santa Rosa island, off the California coast, where the impact was proposed to have occurred. He studied plant and charcoal bits from sediment samples — and looked for minerals, like rare diamonds, that form under intense heat. Anderson says the team didn't find much to suggest a rapid change took place on the ancient landscape.
"The lack of an impact crater; the lack of a contemporaneous killing of the megafauna; the lack of evidence that suggests that the Clovis culture was killed by a widespread environmental event; a lack of wildfires, which are a major aspect of the hypothesis — I think all of this goes to suggest that the time of acceptance of this particular hypothesis is not here," Anderson says.
Scientists continue to look for evidence of past climate events since the last ice age to fill in the gaps of why so many plants and animals disappeared.
