Ice Age Siberian Bear Skull showing possible micrometeorite impacts (Taken by Jon at the Krasnoyarsk Museum this summer.)
34,000 yr old mammoth tusk with detail of confirmed micrometeorite hits surrounded by carbonized rings
Let say you are a woolly mammoth, wandering with your mammoth pals across the North American Savannah, not thinking bout nothin, certainly not the sub-prime mess. It's a good day - the friggin' paleo-indians are leaving you alone for once, no saber tooth tigers are trying to get at the kids, you're just soaking up sun, munching your veggies, thinking maybe this winter head the herd for Nevada, when all of a sudden- what the...? O man!~! a micro-meteorite shower, little grains coming at thousands of kilometers per second! Yow ow ow ow! You don't feel the radiation, at least not right away, but the temperature seems to be rising......,
Bill first pointed out a great work by Paul S. Martin, called Twilight of the Mammoths which lays out the case for human agency in the extinction of the vast majority large land mammals coincident with the timeline for the spread of human populations.
Another line of research has been pursued by Richard Firestone at Lawrence Berkley Labs. The pictures above show micrometeorite impacts on Ice Age mammals and are evidence of the effects from a supernova that hit earth in several waves (separated by thousands of years). The waves included intense radiation, small particles, comets and asteroids. The particles have been analyzed to show composition that is definitely extra terrestrial. Jon Hagstrum has assisted in some of the analysis in the USGS Paleomagnetism Laboratory.
As a part of the waves of cosmic events stemming from the supernova Firestone and buddies have postulated that comet impacted earth about 13,000 years ago accounting for the large mammal extinctions in North America. Summary HERE Check it out.