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.
References:
Awesome recreations of extinct creatures, including the Carboniferous Arthorpleura: http://www.windsofkansas.com/lifesize.html
Fun stuff about the life forms on Earth during the Carboniferous (check out the tab for the Permian as well!):
http://museumvictoria.com.au/melbournemuseum/discoverycentre/600-million-years/timeline/carboniferous/
Read more about the happy go lucky times of the End Permian Extinction:
http://finstofeet.com/2012/08/02/permian-apocalypse/
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”. http://theworldaroundusradio.blogspot.com/2013/02/the-history-of-maine-part-1.html
Maine’s own Geological Survey has a wealth of resources available online: http://www.maine.gov/doc/nrimc/mgs/explore/index.htm
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:
http://www.maine.gov/doc/nrimc/mgs/pubs/online/bedrock/bedrock11x17.pdf
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--http://pubs.usgs.gov/gip/dynamic/understanding.html
(This is exactly the kind of initiative I want my tax dollars spent on! Thanks USGS!)
Monday, March 25, 2013
Sunday, March 17, 2013
The History of Maine: Part 3 The Acadian Orogeny
Note: This program first aired on March 9, 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 430 million years ago. A microcontinent had just crashed into the proto North American plate, and became welded to the coast. This was the Taconic orogeny, and it gave us the Green Mountains of Vermont, as well as some of the land mass of New Hampshire and western Maine.
If you look at any bedrock geology map of the state of Maine, you can see the general pattern of land forms these and subsequent tectonic collisions left on the state. Most of our major geologic forms run from south west to north east, in a diagonal across the state. This is the aspect of the coastline from the original proto North American continent. As additional crust was either welded on to or subducted underneath North America, this diagonal was mostly maintained. Thus the volcanic plutons that resulted from the subduction associated with the Taconic orogeny run from northern New Hampshire (and are in part, named for Hurricane Mountain on the Maine/New Hampshire border) up through northern Maine.
After the afore mentioned collision of the Taconic orogeny, there was a period that was mostly marked by erosion (again!). The Taconic orogeny resulted in very large mountains, which can be thought of simply fodder for the forces of erosion. The bigger the mountain, the more material there is to erode. For our purposes here in tracing the history of Maine, the erosion we are interested in was coming from land and flowing what would now be east to southeast. Terrestrial sediments accumulated of the new shoreline of the proto North American continent. There was a bit of rifting that started to occur to our north and west, so erosion filled that basin as well, which shows up now in far northern Maine. All the while the Iapetus Ocean was still slowly closing, and the continent that would become Europe was still on its collision course with North America.
As the Iapetus closed, the crust that made up the bottom of this ocean was subducted at trenches in the middle of the shrinking ocean, as well as potentially at the edge of either or both of the continents involved. Volcanoes always accompany subduction zones; two bands of volcanoes formed during this period that relate to Maine. One was on the edge of Europe—land that would eventually impact North America, the other was on the edge of what would become central Maine, as it was the leading edge of the North American continent at that time. From about 430 to 400 million years ago, this is what was going on. Erosion was adding to the sediment load in the ocean off the coast of North America, and Europe was drawing ever closer to North America. And I know the anticipation is killing you, but, it takes a while for a collision like this to happen, because the plates only move on the order of 10’s of centimeters a year.
Around 400 million years ago, the collision finally happened. Europe impacted what would become New England. The worst of it was in southern Maine, we can tell because the rocks down there are the most heavily metamorphosed, telling us that they took the hardest hit. Rocks in northern Maine show the least metamorphism, indicating that the force of the impact was minimal there. The impact transformed the mud and silt stones that were forming off the coast before the collision into slate and other metamorphic sedimentary rocks we see in central Maine today.
This impact finished the accumulation of land that would become Maine, and not just due to the folding and morphing of those sedimentary rocks off the coast. It turns out that Europe had its own little love child. Much like the micro continent that had previously impacted North America, Europe had a similar skeleton in its closet. The microcontinent that was welded on to the leading edge of Europe even had a cool name: Avalon* . It was Avalon that slow motion smashed into the coast of Maine, metamorphosing the sediments that were trapped in between the impacting continents. As the last of the Iapetus Ocean disappeared in this collision, the last of the Iapetus Ocean crust was suducted beneath both North America and Avalon, and the melting of that rock gave us the plutons that have become some of our most beloved mountains, the mountians of Baxter State Park to the north and those of Acadia National Park on the coast. The remnants of the Avalon plate itself make up much of the downeast coast and interior.
This impact and the associated mountain building that accompanied it is called the Acadian Orogeny, and it’s importance in creating the land forms we enjoy in Maine can’t be understated. We’ll leave it off there for today, but join us in the coming weeks as we continue piecing together the story of the long and fascinating history of the land that we Mainers call home.
*Actually if you look in the literature, you will see that this microcontinent is referred to by many cool names (don’t you love it when scientists fight?). To me “Avalon” has the best backstory, and is thus the one I prefer.
References:
Yep, these references really hit all the key points: Refer to the list for “The History of Maine: Part 1”. http://theworldaroundusradio.blogspot.com/2013/02/the-history-of-maine-part-1.html
Maine’s own Geological Survey has a wealth of resources available online:
http://www.maine.gov/doc/nrimc/mgs/explore/index.htm
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:
http://www.maine.gov/doc/nrimc/mgs/pubs/online/bedrock/bedrock11x17.pdf
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--http://pubs.usgs.gov/gip/dynamic/understanding.html
(This is exactly the kind of initiative I want my tax dollars spent on! Thanks USGS!)
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 430 million years ago. A microcontinent had just crashed into the proto North American plate, and became welded to the coast. This was the Taconic orogeny, and it gave us the Green Mountains of Vermont, as well as some of the land mass of New Hampshire and western Maine.
If you look at any bedrock geology map of the state of Maine, you can see the general pattern of land forms these and subsequent tectonic collisions left on the state. Most of our major geologic forms run from south west to north east, in a diagonal across the state. This is the aspect of the coastline from the original proto North American continent. As additional crust was either welded on to or subducted underneath North America, this diagonal was mostly maintained. Thus the volcanic plutons that resulted from the subduction associated with the Taconic orogeny run from northern New Hampshire (and are in part, named for Hurricane Mountain on the Maine/New Hampshire border) up through northern Maine.
After the afore mentioned collision of the Taconic orogeny, there was a period that was mostly marked by erosion (again!). The Taconic orogeny resulted in very large mountains, which can be thought of simply fodder for the forces of erosion. The bigger the mountain, the more material there is to erode. For our purposes here in tracing the history of Maine, the erosion we are interested in was coming from land and flowing what would now be east to southeast. Terrestrial sediments accumulated of the new shoreline of the proto North American continent. There was a bit of rifting that started to occur to our north and west, so erosion filled that basin as well, which shows up now in far northern Maine. All the while the Iapetus Ocean was still slowly closing, and the continent that would become Europe was still on its collision course with North America.
As the Iapetus closed, the crust that made up the bottom of this ocean was subducted at trenches in the middle of the shrinking ocean, as well as potentially at the edge of either or both of the continents involved. Volcanoes always accompany subduction zones; two bands of volcanoes formed during this period that relate to Maine. One was on the edge of Europe—land that would eventually impact North America, the other was on the edge of what would become central Maine, as it was the leading edge of the North American continent at that time. From about 430 to 400 million years ago, this is what was going on. Erosion was adding to the sediment load in the ocean off the coast of North America, and Europe was drawing ever closer to North America. And I know the anticipation is killing you, but, it takes a while for a collision like this to happen, because the plates only move on the order of 10’s of centimeters a year.
Around 400 million years ago, the collision finally happened. Europe impacted what would become New England. The worst of it was in southern Maine, we can tell because the rocks down there are the most heavily metamorphosed, telling us that they took the hardest hit. Rocks in northern Maine show the least metamorphism, indicating that the force of the impact was minimal there. The impact transformed the mud and silt stones that were forming off the coast before the collision into slate and other metamorphic sedimentary rocks we see in central Maine today.
This impact finished the accumulation of land that would become Maine, and not just due to the folding and morphing of those sedimentary rocks off the coast. It turns out that Europe had its own little love child. Much like the micro continent that had previously impacted North America, Europe had a similar skeleton in its closet. The microcontinent that was welded on to the leading edge of Europe even had a cool name: Avalon* . It was Avalon that slow motion smashed into the coast of Maine, metamorphosing the sediments that were trapped in between the impacting continents. As the last of the Iapetus Ocean disappeared in this collision, the last of the Iapetus Ocean crust was suducted beneath both North America and Avalon, and the melting of that rock gave us the plutons that have become some of our most beloved mountains, the mountians of Baxter State Park to the north and those of Acadia National Park on the coast. The remnants of the Avalon plate itself make up much of the downeast coast and interior.
This impact and the associated mountain building that accompanied it is called the Acadian Orogeny, and it’s importance in creating the land forms we enjoy in Maine can’t be understated. We’ll leave it off there for today, but join us in the coming weeks as we continue piecing together the story of the long and fascinating history of the land that we Mainers call home.
*Actually if you look in the literature, you will see that this microcontinent is referred to by many cool names (don’t you love it when scientists fight?). To me “Avalon” has the best backstory, and is thus the one I prefer.
References:
Yep, these references really hit all the key points: Refer to the list for “The History of Maine: Part 1”. http://theworldaroundusradio.blogspot.com/2013/02/the-history-of-maine-part-1.html
Maine’s own Geological Survey has a wealth of resources available online:
http://www.maine.gov/doc/nrimc/mgs/explore/index.htm
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:
http://www.maine.gov/doc/nrimc/mgs/pubs/online/bedrock/bedrock11x17.pdf
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--http://pubs.usgs.gov/gip/dynamic/understanding.html
(This is exactly the kind of initiative I want my tax dollars spent on! Thanks USGS!)
Tuesday, March 5, 2013
The History of Maine: Part 2 The Taconic Orogeny
Note: This program first aired on March 2, 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 500 million years ago; an ocean called the Iapetus was open in essentially the same spot relative to the continental landmasses as today’s Atlantic ocean, and during that time terrestrial sediments were slowly building up on the continental margins of what would become North America.
At this time the edge of the continental mass that will become North America was located much further inland than it is today, around the St. Lawrence seaway. Some of the rocks that would become greater New England were formed as sedimentary rock being deposited off the coast, the result of millions of years of erosion during the relatively quiet time of the Iapetus Ocean. All good things must come to an end however, and about 500 million years ago, the Iapetus Ocean reversed course and began to close. An ocean doesn’t just close on its own accord, it closes because the continents on either side of it start moving towards each other, propelled by what is not exactly worked out. Heat is constantly moving in the deeper layers of the Earth, what you learned as the mantle and the core back in grade school. It is thought that that heat melts the material of the mantle and core, and that molten rock moves in ultra slow convection currents deep inside the earth. When that moving material gets close enough to the crust it can actually drag the crust along. That is the idea anyway. What the closing of the Iapetus actually looked like is the subject of much speculation, as it is likely that the spreading center at the mid ocean ridge in the middle of the Iapetus continued to function in some fashion, so for the ocean basin to actually close, oceanic crust had to get destroyed at a high rate, which happened at the subduction zones that formed, unusually, out at sea.
A subduction zone is a place where one piece of crust is forced underneath another one. The one that goes underneath, the subducted one, travels down until it meets the very hot material from inner Earth, where it generally melts. We up here on the surface call melted rock lava, and yes, volcanoes form as a result of subduction zones. Think of the Cascade Mountains, or the volcanic islands of the Aleutian Island chain, or the Andes. These volcanic mountains are all formed from subduction zones, where oceanic crust is being forced down into the mantle. *
So back during the closing of the Iapetus, subduction zones were forming along with their accompanying volcanoes, and the crust that made up the bottom of the Iapetus Ocean was disappearing (I like to think of it as being recycled) as the area of the ocean decreased. The Iapetus Ocean had one other significant feature that plays into this story as well. It wasn’t an uncluttered ocean like today’s Atlantic, the Iapetus featured at least one, if not more micro continents, also called terranes, as well as all the volcanic islands that were forming from the subduction of the ocean crust. I imagine that a modern day equivalent would be the sea around Indonesia and the island of New Guinea. These are small chunks of continental crust, not attached to a larger continental land mass (though they likely were, and were simply torn asunder during one of the supercontinent break up cycles).
So now we have all the pieces for what happened next, sedimentary rock and oceanic crust off the continental margin of proto North America, and volcanic islands and random continental terranes in the closing Iapetus. Approximately 480 to 430 million years ago, as the Iapetus basin continued to close, and the land masses of proto Europe and proto North America moved towards each other, one of these smaller terranes crashed into proto North America (it is a slow motion crash, much like the slow motion crashes going on in south east Asia today). It was a messy crash and as the terrane was being sutured or welded on to the North American plate, lots of that sedimentary rock that formed off the continental margin, as well as big chunks of oceanic crust were thrust up and pinched in between the two colliding plates. You can see evidence of this suture in central Vermont and southern Quebec and much the Boundary Mountains province of western Maine is made of that small terrane that collided with proto North America. Its important to remember that at this point, the proto European continent hasn’t arrived to the tectonic party yet, the only collision that had occurred at this point was between proto North America, and the small terrane from somewhere in the middle of the ocean. This event is known as the Taconic Orogeny, orogeny meaning mountain building event, and as far a Maine is concerned, it gave us a good amount of our current land mass.
We’ll leave it off there for today, but join us in the coming weeks as we continue piecing together the story of the long and fascinating history of the land that we Mainers call home.
* Subduction zones are also home to the deepest parts of the ocean. As the two plates meet and one gets sucked down under the other, that downward movement forms a trench, and these trenches get quite deep. The deepest spot of the ocean is in the Marianas Trench, where the Pacific plate is being subducted under the Philippine Plate, and is nearly 37,000 ft. deep. We send a “manned” submersible down there to explore in 1960, and then it was not visited by people again until 2012, when movie director and apparent aquanaut James Cameron financed his own expedition and made history by being the third human to get to the bottom of the deepest part of the ocean.
References:
Same as for “The History of Maine: Part 1”.
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 500 million years ago; an ocean called the Iapetus was open in essentially the same spot relative to the continental landmasses as today’s Atlantic ocean, and during that time terrestrial sediments were slowly building up on the continental margins of what would become North America.
At this time the edge of the continental mass that will become North America was located much further inland than it is today, around the St. Lawrence seaway. Some of the rocks that would become greater New England were formed as sedimentary rock being deposited off the coast, the result of millions of years of erosion during the relatively quiet time of the Iapetus Ocean. All good things must come to an end however, and about 500 million years ago, the Iapetus Ocean reversed course and began to close. An ocean doesn’t just close on its own accord, it closes because the continents on either side of it start moving towards each other, propelled by what is not exactly worked out. Heat is constantly moving in the deeper layers of the Earth, what you learned as the mantle and the core back in grade school. It is thought that that heat melts the material of the mantle and core, and that molten rock moves in ultra slow convection currents deep inside the earth. When that moving material gets close enough to the crust it can actually drag the crust along. That is the idea anyway. What the closing of the Iapetus actually looked like is the subject of much speculation, as it is likely that the spreading center at the mid ocean ridge in the middle of the Iapetus continued to function in some fashion, so for the ocean basin to actually close, oceanic crust had to get destroyed at a high rate, which happened at the subduction zones that formed, unusually, out at sea.
A subduction zone is a place where one piece of crust is forced underneath another one. The one that goes underneath, the subducted one, travels down until it meets the very hot material from inner Earth, where it generally melts. We up here on the surface call melted rock lava, and yes, volcanoes form as a result of subduction zones. Think of the Cascade Mountains, or the volcanic islands of the Aleutian Island chain, or the Andes. These volcanic mountains are all formed from subduction zones, where oceanic crust is being forced down into the mantle. *
So back during the closing of the Iapetus, subduction zones were forming along with their accompanying volcanoes, and the crust that made up the bottom of the Iapetus Ocean was disappearing (I like to think of it as being recycled) as the area of the ocean decreased. The Iapetus Ocean had one other significant feature that plays into this story as well. It wasn’t an uncluttered ocean like today’s Atlantic, the Iapetus featured at least one, if not more micro continents, also called terranes, as well as all the volcanic islands that were forming from the subduction of the ocean crust. I imagine that a modern day equivalent would be the sea around Indonesia and the island of New Guinea. These are small chunks of continental crust, not attached to a larger continental land mass (though they likely were, and were simply torn asunder during one of the supercontinent break up cycles).
So now we have all the pieces for what happened next, sedimentary rock and oceanic crust off the continental margin of proto North America, and volcanic islands and random continental terranes in the closing Iapetus. Approximately 480 to 430 million years ago, as the Iapetus basin continued to close, and the land masses of proto Europe and proto North America moved towards each other, one of these smaller terranes crashed into proto North America (it is a slow motion crash, much like the slow motion crashes going on in south east Asia today). It was a messy crash and as the terrane was being sutured or welded on to the North American plate, lots of that sedimentary rock that formed off the continental margin, as well as big chunks of oceanic crust were thrust up and pinched in between the two colliding plates. You can see evidence of this suture in central Vermont and southern Quebec and much the Boundary Mountains province of western Maine is made of that small terrane that collided with proto North America. Its important to remember that at this point, the proto European continent hasn’t arrived to the tectonic party yet, the only collision that had occurred at this point was between proto North America, and the small terrane from somewhere in the middle of the ocean. This event is known as the Taconic Orogeny, orogeny meaning mountain building event, and as far a Maine is concerned, it gave us a good amount of our current land mass.
We’ll leave it off there for today, but join us in the coming weeks as we continue piecing together the story of the long and fascinating history of the land that we Mainers call home.
* Subduction zones are also home to the deepest parts of the ocean. As the two plates meet and one gets sucked down under the other, that downward movement forms a trench, and these trenches get quite deep. The deepest spot of the ocean is in the Marianas Trench, where the Pacific plate is being subducted under the Philippine Plate, and is nearly 37,000 ft. deep. We send a “manned” submersible down there to explore in 1960, and then it was not visited by people again until 2012, when movie director and apparent aquanaut James Cameron financed his own expedition and made history by being the third human to get to the bottom of the deepest part of the ocean.
References:
Same as for “The History of Maine: Part 1”.
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