Re: Tunguska
See the summaries of recent studies on Tungusta.
http://www-th.bo.infn.it/tunguska/tu99public.htm
In the second one listed, it is claimed that peat samples from the impact region show carbonaceous chondrites, of extraterrestrial origin.
It was my impression that scientists and astronomers were pretty much unanimous in their view that the Tungusta event was caused by a comet, or meteor, that exploded about 8 km above the ground.