Doug Macdougall

Considering what a radical notion it was when introduced, it’s appropriate that the first person to use the phrase “ice age”, German botanist Karl Schimper in 1837, died in a mental asylum.

Louise Aggasiz, better known for his work on fossil fish, was the first to seriously argue for glacial episodes in the earth’s past – even if he was curiously uninterested in the causes of those episodes. The forgotten James Croll, a self-taught polymath and Scotsman, put forth the notion of astronomical cycles which was further refined by Serbian mathematician Milutin Milankovitch. Macdougall tells a lot of his story about earth’s ice ages through the biography of these men as well as the story of J. Harlan Bretz, the man who was denigrated by most of the geologic profession for his seeming violation of the cardinal principle of uniformitarianism (geologic forces of the past must be ones we see today) when he proposed that the enigmatic Channeled Scablands of Washington State were created over the course of a few days when a massive glacial dam burst.

Macdougall’s presentation is smooth and clear from the graphs that illustrate earth’s five major ice ages – including the one that we are still in the midst of – to the reconstruction, through a variety of methods, of the climate of the last 1,000 years. He lays out clearly the analytical techniques used to establish earth’s climatic past – including what we are confident about and what we merely suspect.

We often hear that changes in earth’s climate propelled the evolution of man’s hominid ancestors. Usually this is a vague mention of shrinking woodlands in Africa. Macdougall, building on the work of paleontologist Steven Stanley, goes into more useful detail. He explains that shrinking woodlands created islands where isolated populations of humans mutated (a process known as allopatric speciation) and, when the climate warmed again, their new adaptations expanded into new areas. He also mentions the idea of that the great Cambrian explosion of new forms of life may have been caused the fluctuating climate of the Proterzoic ice age.

In short, this is an excellent primer on the current stage of our understanding about our present and past ages of ice.… (lisätietoja)