About 10 million square kilometers (approximately 10% of the land area) was consumed by fires 12,800 years ago.
The reason for this Dantesque fire was due to cosmic impact, according to a study of geochemical and isotopic markers recently published in the Journal of Geology.
The work includes measurements made at more than 170 different sites worldwide and has involved 24 researchers, including Professor Emeritus of Physics and Astronomy at the University of Kansas Adrian Melott and the Professor Brian Thomas, a doctorate of 2005 in Kansas.
The disaster was triggered when Earth collided with fragments of a disintegrating comet that was approximately 100 kilometers in diameter. As he explains Melott:
The hypothesis is that a large comet fragmented and the fragments impacted the Earth, causing this disaster. Several different chemical signatures, carbon dioxide, nitrate, ammonia and others, seem to indicate that an astounding 10 percent of Earth's land surface, or about 10 million square kilometers, was consumed by fires. Pollen analysis suggests that pine forests were probably burned to be replaced by poplars, which is a species that colonizes cleared areas.
Calculations suggest that the impact would have depleted the ozone layer, causing increases in skin cancer and other negative health effects. However, for now, everything is a mere hypothesis.