Note: This program first aired on February 23, 2013.
We’re starting a series here on the World Around Us, about the history of Maine. And when I say history, I mean all the history, starting before there was even any land that would eventually become the great of Maine. Its true, though maybe hard to believe for diehard Mainers, 700 million years ago, there was no Maine.
At that time, all of the continents were grouped together into one giant super continent, but not the one you think. No it wasn’t Pangea, it was Pangea’s predecessor, the little known Rodinia. In fact it is hypothesized that for the past 2 and a half to 3 billion years of Earth’s history, the Earth’s crust cycled through as many as 10 or 12 supercontinents, each meeting the same eventual fate, the big break up. Much of the land that would be come Maine didn’t exist at all, and what would become the east coast of the continent of that would eventually become North America was in the middle of this super continent.
Its easy to be casual when trying to pin point a specific time period in geologic time. 600 million years ago, or was it 570 million? Or 590 million? What’s 30 million years here or there? Well actually, 30 million years is a very long time. Longer than humans have been around by 29.8 million years, longer than the most recent period of ice ages by 28 million years, long enough for significant geologic events to have occurred. So we will try not to be too flippant, and round off too grossly when referring to these numbers that are so astronomically we can’t get our big fat human brains* around them.
So about 600 million years ago, this super continent started to break up. A rift formed in the middle of this group of continental land masses, much like the rift that is slowly pulling apart in East Africa today. As the continents pulled apart, new oceanic crust formed in between them at the seam where they ripped. The continents moved away from each other as if on a conveyer belt, and the space between them got wider and wider, as volcanic activity at the seam created new oceanic crust. This is happening today in the Atlantic. North America and Europe are moving away from each other, and the seam that marks where they were originally joined is out in the middle of the Atlantic Ocean, called the mid Atlantic Ridge. Most of the mid Atlantic Ridge is underwater, but you can see it in action in Iceland.
600 million years ago, when Rodinia broke apart, the ocean that started to form in between the chunks of continent that eventually became North America and Europe has been named the Iapetus. This demonstrates that geologists love Greek mythology, as Iapetus was a titan, who fathered Atlas—the fellow who shouldered the world, and after whom the Atlantic ocean is named. So the fact that the next ocean to be created after the Iapetus was named the Atlantic, after Atlas, was not a coincidence.
The Iapetus Ocean was open for perhaps as much as 100 million years, during which time there was plenty of opportunity for our old friend erosion to wash much terrestrial sediment from land into the oceans, especially near the continental margins. This was the main geologic feature of this time period, at least as far as Maine was concerned, because during this time, some of the rock that would become Maine, or at least, greater New England was being deposited in these eroded sediments.
Though this is a story of geology, and the balance between tectonic action and erosion, it happens to coincide with a major development in biology and evolution as well. At that time Earth’s atmosphere was similar to what it is today, interms of its oxygen content (that being about 21% oxygen). This wasn’t always the case, Earth started out with no free oxygen gas, and it was only through the development of photosynthetic bacteria that oxygen levels in the atmosphere began to rise. This increased oxygen content is thought to be one of the factors that led to the explosion of life that was about to happen as the Iapetus was opening up. Multicellular life was just starting to evolve, and the vast majority of life on Earth at that time was thought to be bacterial. While the geology of this era had a timeless, repetitive quality, biologically things on Earth were about to change in ways unseen up to that point.
We’ll leave it off there for today, but join us in the coming weeks as we continue this story piecing together the long and fascinating history of the land that we Mainers call home.
*I mean this in the best possible sense, our brains are made primarily of fat (and fat means lipids, not just fat cells like the ones we store all over the rest of our bodies).
References:
The Introduction to the Roadside Geology of Maine by D.W. Caldwell is a terrific over view of the formation of the land that became Maine. As a side note, my great grandmother was a Caldwell from western Maine, and though I have yet to prove it with geneology, I’d like to claim D.W. in my pedigree.
The Canadian book The Atlantic Coast: A Natural History by Harry Thurston, provides details on the evolutionary stages of life that were occurring during all of this geological upheaval, and has many gorgeous photographs too, eh?
Nice material here on super continent formation from the Burke Museum of Natural History and Culture (University of Washington, Seattle)-- note: it is decidedly Pacific Northwest in flavor: http://www.burkemuseum.org/static/geo_history_wa/Dance%20of%20the%20Giant%20Continents.htm
This site features a great series of maps of the positions of the plates during most of the time periods I talked about in this episode (put together by some nutty British fossil hunters) : http://www.discoveringfossils.co.uk/how_britain_formed.htm
