Monday, March 25, 2013

The History of Maine: Part 4 The Carboniferous/Permian Interlude

Note: This program first aired March 23, 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 about 360 million years ago. The Iapetus Ocean (the predecessor to today’s Atlantic Ocean) had just finished closing, and was gone for good. The continental land mass that today we call Europe had just collided with North America, crushing coastal sediments and causing volcanic activity at and around the edges of the two plates. Geologists refer to this collision as the Acadian Orogeny, and aspects of it did indeed give us the mountains of Acadia National Park.

At this point, Maine, a state known for all of its beautiful coastline, was decidedly inland. To the what will be west we had the extent of North America. To the what will be east, we had the Eurasian continent. Maine was right in the middle. And this is how it stayed, for another 100 million plus years. These years included two major geological periods, the Carboniferous and the Permian. Geologically during these time periods all of the continental land masses were coalsesing, into the familiar super continent we all know and love, Pangea. In terms of North America, the formation of Pangea was completed 300 to 250 million years ago, when the Africa (accompanied by the rest of Asia), smashed into what would become the southern United States, in what eologists call the Alleghanian Orogeny. This tectonic event didn’t do much to the geology of Maine, though there is some speculation that the impact caused some shifting along the faults that sutured Avalon to North America. The completion of the formation of Pangea though, did influence the global climate, drying things out slightly in an otherwise tropical and moist environment.

While we wait for the next major geological happening, lets take a slight detour and look a the biology of the time period while Maine was just sitting there in the middle of the super continent. The Carboniferous period ran from about 350 to 300 million years ago, and is known as the Age of Ferns. Picture a majestic forest, but instead of trees, the plants towering over your head are ferns, and horsetails and club mosses. During the Carboniferous, plants had fully migrated on to land from the oceans, but were still mainly of the vascular, non flowering, spore bearing type. Today these kinds of plants are much more diminuitive, but in the Carboniferous, they reigned supreme. Conifers, the first true seed bearing plants were just getting going in the drier areas of this warm wet world. The Carboniferous is named for the major geologic feature of the time, the massive coal beds that started as these lush living forests. Due to all this lushness, as well as the large amount of erosion and burial of organic matter, oxygen levels were higher during this time period than any other time before or since. These high oxygen levels (as high at 35% of the composition of the atmosphere) allowed for gigantism in another group of organisms, ones that today are generally much smaller than during the Carboniferous; athropods. This is the time of the 6 foot long arthropod called Arthopleura, and the dragonfly with three foot wing span. Arthropods do not actively inhale air, but simply let it diffuse into their bodies through a series of tubes called the tracheal system. The rate of gas diffusion is thought to be a limiting factor on body size, so the higher oxygen content (the biologically most important gas) would release some of that limitation, allowing for larger (much larger!) arthropods.

Amphibians were another group of animals that were starting to make a name for themselves during this time. Terrestrial tetrapods were abounding, and included a group that evolved out of the amphibians, to become our animal ancestors: the amniotes. They were named thus because of they had evolved an amniotic membrane, that allowed their eggs to be laid on land instead of in the water. This group rapidly split into two distinct lines; the synapsids included animals that eventually evolved into mammals, and the sauropsids, animals that evolved into reptiles (including birds and dinosaurs).

During the Carboniferous and the Permian, climate fluctuated from warm, wet and swampy, to warm and dry, with a bit of ice cap activity thrown in. Throughout it all, evolution was proceeding in leaps and bounds. All good things though come to an end, and at the end of the Permian period, about 250 mya, Earth experienced the biggest mass extinction ever. The End Permian eliminated as many as 90 % of all species on Earth at the time. Evolutionarily, mass extinctions are like hitting the reset button. All the species that we find on Earth today are some how related to those 10% of survivors. The cause of the End Permian is thought to be a massive volcanic eruption event, one that lasted perhaps a million years, changing the composition of green house gasses in the atmosphere and dramatically altering climate and atmospheric and ocean chemistry. The details are still hotly debated, but regardless of how it happened, the End Permian event was one for the record books.


Awesome recreations of extinct creatures, including the Carboniferous Arthorpleura:

Fun stuff about the life forms on Earth during the Carboniferous (check out the tab for the Permian as well!):

Read more about the happy go lucky times of the End Permian Extinction:
This blogger hasn’t referenced his material, but it isn’t too bad and provides a nice overview.

Yep, these references really hit all the key points:  Refer to the list for “The History of Maine: Part 1”.

Maine’s own Geological Survey has a wealth of resources available online:
This is a link to a pdf of a simplified bedrock geology map of the state of Maine, clearly showing the southwest/northeast trend of bedrock:

 Our friends at the US Geological Survey have some nice material on plate tectonic basics, including information about just how they know how fast the plates move--
 (This is exactly the kind of initiative I want my tax dollars spent on! Thanks USGS!)