Charcoal from Comets, Asteroids and Wildfires
Tom Miles, May 28, 2007
There is speculation that pockets of charcoal that resulted in enriched soil came variously from comets and asteroids and resulting wildfires, as well as intentional burning. The latest comet event has been reported as 12,900 years ago in North America. See Science Daily:
Did A Comet Hit Great Lakes Region, Fragment Human Populations, 12,900 Years Ago? May 23, 2007
and National Geographic News:
Comet Wiped Out Early North American Culture, Animals, Study Says May 23,2007
Potential extraterrestrial causes of terra preta formation are discussed in the literature from Cornell University and elsewhere. It has also been debated on the Hypography Science Forum.