Did an extra-terrestrial impact over the Laurentian Ice Sheet cause the extinction of North America’s mega-fauna, the disappearance of Clovis culture and the onset of the Younger Dryas Cooling ?

Gilbert N. Hanson
Department of Geosciences
Stony Brook University

Sunday, May 18, 2008 at 2:00 P.M.
Room 319
American Museum of Natural History New York City

A team of 26 scientists has proposed that 12,900 years ago a comet broke up and exploded over the Laurentian Ice Sheet with the force of millions of atomic bombs (Firestone et al, 2007). This impact event would have caused the extinction of the North American mega-fauna which included animals such as mammoths and saber tooth tigers; the disappearance of the Clovis culture and the onset of a severe cooling of the North Atlantic area known as the Younger Dryas.

The extinctions of the mega-fauna would have been a result of the impacts’ shock wave, then massive wildfires followed by a dramatic reduction of food associated with climate change.

Evidence for the impact includes a black algal mat that overlies the latest Clovis sites throughout North America. The mat contains charcoal, tiny spheres of carbon and metals, nanodiamonds, and extraterrestrial concentrations of helium-3 and the element iridium.

At the time of the impact the climate had become warmer than it had been for a few thousands of years after the Last Glacial Maximum. The impact caused massive melting of the Laurentian Ice sheet which produced fresh water which entered the North Atlantic Ocean and stopped the thermohaline circulation. This led to a ca 1000 year cold period when temperatures approached those during the Last Glacial Maximum. This cooling period is known as the Younger Dryas. After the Younger Dryas the warm Holocene Epoch, that we are presently in, began.

In this presentation we will consider the climatic and glacial setting, the timing of the events and the evidence for an extra terrestrial impact.