Note: This program first aired May 4, 2013.
We’re spending a few weeks here on the world around us, tracing the deep history of Maine, from its geological genesis to the current day. We left off last week talking about the basic mechanics of continental glaciers, from their formation to their plastic-y deformation and movement.
The most recent ice age on Earth began about two and a half million years ago, and marked the beginning of what geologists refer to as the Quaternary Period. This ice age was the culmination of a gradual cooling trend in Earth’s overall climate that began about 75 million years ago, while dinosaurs still roamed the Earth. On the geologic time scale, two and a half million years is chump change, and when compared to the time required for opening and closing of an ocean or the subduction of a plate, it is hard to believe anything significant could happen to a landscape in such a short time. But believe it. The effects of the ice age absolutely define the hardscrabble nature of Maine’s land forms and biotic communities today.
The ice age that began two and a half million years ago* is actually a series of repeating expansions and retreats of continental glaciers, which originate at high latitudes, and spread into temperate or mid latitudes at their furthest reach. The pattern has been generalized as 100,000 year cycles, about 60-90 thousand years of glaciation, followed by a warmer period lasting 10 to as much as 40 thousand years, but there is certainly variability. These warmer periods are called interglacials, and we are in one right now—if we weren’t, Maine winters and summers would be a whole lot colder than we currently experience.
It is difficult to say with certainty just how many times the continental glacier that originated in northern Canada advanced over the landscape of Maine, as each glacial advance essentially obliterates all evidence left by the glacial advance before it. Billions and billions of pounds of one to two mile thick ice quite literally wipes the slate clean every where it goes. But we do have a very clear picture of the global climate during this time, which gives us a good sense of cooler periods and warmer periods, which are relatively safe to correlate with periods of glacial advance and retreat in the northern hemisphere. The climate record is recorded in the ice sheets that persist today (in Antarctica, in Alaska, in Greenland). Scientists drill into these ice sheets and retract a core (essentially a long skinny tube) of ice. Remembering that glaciers are formed from repeated snow fall, researchers can actually discern the layers of snow, compressed but still distinct, and like scientists looking at tree rings, actually reconstruct the climate history with amazing resolution. Tiny bubbles of gas from the fossil atmosphere and dust, ash and other atmospheric particles are clues that aid this research.
While all this glacial activity was going on, and the Earth was over all a bit cooler and probably a bit drier as well, something else was happening, something we are pretty interested in. Importantly for us, this past ice age coincides with the period of hominid evolution, us. While it is impossible to say that humans evolved because of the ice age, it is true that we evolved in a relatively uncommon climatic regime. In the big picture, Earth has been much much warmer than it is now, humans evolved during a cool spell. While it is hard to predict with any certainty just how hot it will get as a result of human influenced climate change, the possibility that keeps climate scientists up at night is that it will get warmer than humans, ANY humans have ever experienced. That is the kind of climate shift that marks the end of the evolutionary line for many a species. We see it over and over again in the fossil record. That is why many people define climate change as an existential threat, it is estimated that 99% of every species that has lived on Earth is extinct, primarily due to the fact that they were not able to evolve fast enough to adapt to rapidly changing climate regimes. Ice ages come and ice ages go, changing the shape of the land along the way, but probably more importantly, ice ages are a symptom of instability in the global thermostat, with significant repercussions for everything that lives on Earth.
We digressed a bit today, but join us next week as we get back on track and look at the direct impact of the glaciers on the landscape of Maine.
References:
Caldwell, D. W. Roadside geology of Maine
http://nsidc.org/cryosphere/glaciers/life-glacier.html
The National Snow and Ice Data Center (yes there is such a thing!) All About Glaciers!
Super nerds unite: check out the Maine Ice Age Trail, and you too can tour Hancock and Washington counties looking at gravel pits (I’ve done it, its awesome). http://iceagetrail.umaine.edu/ also includes an excellent overview of the last ice age in Maine http://iceagetrail.umaine.edu/content/iceageinmaine/iceageinmaine.php
Nice bigger picture material from PBS (written quite a while ago by a UMaine researcher):
http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html
Some scholarly business, though there has been a flurry of research in the past two decades on ice sheets, so this is likely a bit dated: Richmond, G.M. and D.S. Fullerton, 1986, Summation of Quaternary glaciations in the United States of America. Quaternary Science Reviews. vol. 5, pp. 183-196
On Extinction—From the Bristol University late Triassic Website: http://palaeo.gly.bris.ac.uk/palaeofiles/triassic/extinction.htm
Explore UMaine’s Climate Change Institute http://climatechange.umaine.edu/ especially this link to the basics of ice core research:
http://climatechange.umaine.edu/icecores/IceCore/Ice_Core_101.html
