Tuesday, January 6, 2009

Ice Age

When we think about the “Ice Age,” we think of it as one single occurrence. But I was surprised to find out that was not the case. Where was I in Earth History class?

During the last 1 billion years of Earth’s history, the Earth is approximately 4.5 billion years old, we have had many glacial advances and retreats. They are concentrated into four time intervals, not randomly distributed throughout Earth’s history like one might think.

Large, important glaciations occurred during the late Proterozoic (between 800 and 600 million years ago), the Pennsylvanian and Permian (between 350 and 250 million years ago) and during the late Neogene to Quaternary (the last 4 million years.) Less extensive glaciations occurred during portions of the Ordovician and Silurian (between 460 and 430 million years ago.) The last “Ice Age” ended around 15,000 years ago. Overall, however, there have been more than 60 glacial advances and retreats during the last 2 million years.

If "Ice Age" is used to refer to long, generally cool, intervals during which glaciers advance and retreat, we are still in one today. Our modern climate represents a very short, warm period between glacial advances. Scientist believe it may be climate change, but it also could be nothing more than a normal long-period climatic variation.

Now you’re a little smarter, Girlfriend — And so am I.

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