Ice Age Theory Challenged

Some scientists have argued for a few years that the most recent ice age in the northern hemisphere of Earth came to a crashing close something more than 12,000 years ago when a comet or asteroid either slammed into Earth or exploded in midair, altering the climate for the warmer. That theory, kin to the one that holds an asteroid impact killed off the classic dinosaurs, leaving modern birds to continue that line, is an example of catastrophism, a view that large events have played a major role in shaping Earth's natural history.

A new study rejects the comet theory, however, arguing that the change in the sediment record used by supporters of the theory in fact extends over roughly five thousand years. It does not, therefore, point to a single event. Further, they argue, the chemical changes could have been produced naturally by fungus.

Climate, as revealed in the geologic and fossil records, swings between warm periods, like the current one which has seen the rise of human civilization, and ice ages over tens or hundreds of thousands of years. Holding that an asteroid or comet impact triggered each shift may be difficult to sustain. Such events could be responsible for specific shifts, but separating out exactly which ones would seem to be a real challenge.