> The problem I have with this is the lack of brand new meteor craters to
> support the concept. One of most recent craters is the BArringer crater and
> it is 50 000 years old. If this hypothesis is true there should be some
> physical evidence in the form of very young, very fresh craters. I know of
> none. Do you?
Sometime during the mid- to late Seventies I read an article about
carbonaceous chondrites (CC). In it the authors suggested that, because they
tended to be light and delicate compaired to stoney or metal meteorites, they
also tended to explode in the atmosphere rather than impact the ground. They
suggested that a CC was the explanation for Tunguska.
Whether or not this is true, the Tunguska event represents a possible answer
to Glenn's question. No crater was ever found in Siberia, yet the
atmospheric explosion still managed to throw enough dust and soot into the
air to affect the weather for some years after. An alternative answer would
be impacts in the oceans, which would leave no obvious craters but could
still throw up enough material into the atmosphere to change the weather for
a few decades.
My main objection to this theory is that it sounds too much like "jumping on
the bandwagon"; impact disasters are now trendy and people are starting to
claim them as causes for events simply for that reason. I would think a
better explanation for possible historical climate changes would be volcanic
activity. Even an eruption as small as Pinatubo affected the weather for a
number of years; an eruption only 10 to 50 times larger might be enough to
create the disaster needed to bring down a civilization.
Kevin L. O'Brien