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The current impact hypothesis states that the air burst(s) or impact(s) of a swarm of carbonaceous chondrites or comet fragments set areas of the North American continent on fire, causing the extinction of most of the megafauna in North America and the demise of the North American Clovis culture after the last glacial period.
The Younger Dryas ice age lasted for about 1,200 years before the climate warmed again.
Albert Goodyear indicate that the sediments containing these artifacts are at least 50,000 years old, meaning that humans inhabited North American long before the last ice age.
The authors stated that the data required further analysis, and independent analysis of other Clovis sites for verification of this evidence. Kennett reported that the nanodiamonds were evidence for bolide impacts from a rare swarm of carbonaceous chondrites or comets at the start of Younger Dryas, resulting from multiple airbursts and surface impacts.
The authors stated that they remained skeptical of the bolide impact hypothesis as the cause of the Younger Dryas and the megafaunal extinction. This resulted in substantial loss of plant life, megafauna and other animals.
One group examined carbon-14 dates for charcoal particles that showed wildfires occurred well after the proposed impact date, and the glass-like carbon was produced by wildfires and no lonsdaleite was found.
The study of black mats, that are common in prehistorical wetland deposits which represent shallow marshlands, that were from 6000 to 40,000 years ago in the southwestern USA and Atacama Desert in Chile, showed elevated concentrations of iridium and magnetic sediments, magnetic spherules and titanomagnetite grains.