Note: This program first aired on March 30, 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 with the mass extinction event that marked the end of the Permian period, an era of Earth history that came to a dramatic closure about 250 million years ago. All of us animals here on Earth today are some how related to the hearty 10% or so of species that survived this cataclysmic event (plants seemed to have weathered the end Permian much better, mostly surviving into the Mesozoic).
A bit after the end of the Permian age, and possibly related to it, the crust that made up the super continent of Pangea started to weaken. Tectonic forces from the Earth’s mantle and core were awaking, or at least changing direction, and the continents that had been crushed together started to pull apart again. This tension started gradually, about 225 million years ago; by 200 million years ago the continents were separating in earnest. The rifting we are most interested is that which returned the land that would become Maine to the coast. Remember, during the duration of Pangea, Maine was most decidedly inland.
The continents that would eventually become known as North America and Europe had previously drifted towards each other as the Iapetus Ocean closed. Now, they pulled apart from each other, on essentially the same line as the Iapetus Ocean. As the continents pulled apart, a rift formed between them. At first it was likely just an inland valley, much like the East African Rift Valley today, spotted with long narrow lakes and volcanoes. As it grew wider, one end or the other of it eventually contacted the global ocean, and was inundated with sea water. Voila! An ocean was born. To see this in action today, you need look no farther than the Red Sea—an ocean flooded extension of the rift valley from East Africa.
The ocean that formed of course, is our own dear Atlantic Ocean, named for Atlas, the titan of Greek mythology, who was the son of Iapetus. So clever. And I’ve said that it formed in nearly the same location as the ancestral Iapetus. Nearly, but not exactly, and here is why. Some of the small bits of land, the micro continents, terranes and crushed coastal sediments, that were accreted on to the coast lines of North American and Europe, they stayed accreted, or stuck to the larger continental land masses, instead of getting dragged back out to sea. These bits of land added more “continent” to the continents, and gave the land masses new coastlines as the sea filled in the growing gap between North America and Europe. Of particular relevance for Maine, the microcontinent called Avalon stayed stuck to our coast line, and today makes up much of Hancock and Washington Counties, and a thin strip of coast on the west side of Penobscot Bay.
The opening of the Atlantic Ocean was the last major tectonic event to affect the land we now call Maine. The youngest rocks in the state date to this time period. When the continents were under tension and were pulling apart, many cracks formed in the crust. As these cracks formed, they were quickly filled in by hot fluid magma from deep within the crust, forming intrusions called dikes. This magma cooled into basalt, a rock type that makes up most of the crust of the bottom of the ocean. It is typified by being dark in color and fine grained. In many places along the coast, you can recognize these basalt dikes by their dramatic dark color, in an otherwise light granitic rock. After these dikes formed, there was no more igneous activity, no more volcanoes, no more rifting. At this point in history, Maine settled in for about 200 million years of erosion, which removed much of the material that was covering the mountains and hills we see around us today. These rocks started many miles below the surface, and are only on the surface today due to the constant pressure of the forces of erosion.
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. Next week we take a big leap in time, and change the scale of our gaze as well, as we begin to look at the ice age as the next “big thing” in the history of Maine.
References:
Yep, these references really hit all the key points: same as for “The History of Maine: Part 1”. http://theworldaroundusradio.blogspot.com/2013/02/the-history-of-maine-part-1.html
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, April 2, 2013
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.
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!)
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!)
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”.
Saturday, February 23, 2013
The History of Maine: Part 1
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
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
Sunday, February 17, 2013
Erosion
Note: This program first aired on February 9, 2013.
The movement of the plates that makeup the earth’s crust causes earthquakes, yields volcanoes and ultimately results in orogeny, or the uplift of mountains. In the story we tell ourselves about the world, these forces are cast in dramatic roles (whether or not they really deserve them is for a different day). Volcanoes and earth quakes are exciting (if also dangerous), mountains soar above us, the alpine realm virtually synonymous with adventure. Today though, we turn away from these easy to tell tales, to explore the other side of the coin. Remember, in the universe for every action, there is an equal and opposite reaction. And while we are easily distracted and entertained by the expansive spectacle of orogeny, you need to be aware that there is another force at work in the universe. A subversive force, one that constantly and endlessly eats away at the world as we know it, seeking equilibrium. This leveling energy is most commonly known and experienced as erosion.
In physics there is a concept called entropy, which states that systems will tend from states of order to states of disorder, if isolated from additional inputs that would decrease the disorder. Basically put—without input of energy, things gradually fall apart. One way to define a living being is that it is anti entropy, by being alive the life form is using a constant input of energy to combat the tendency towards disorder of its molecules and atoms. Death is when entropy finally wins.
Erosion is entropy in the geologic frame of reference. Mountains may rise up, rocks may form bed rock, but little by little they will be broken down and, given enough time, flattened and brought back down to earth. The mechanism of erosion is called weathering, and can happen either mechanically or chemically. The easiest one to think about is mechanical weathering, we all understand about the physical break down of material. Big rocks turn into small rocks, small rocks turn into pebbles, pebbles turn into sand, sand turns into…well you get the idea. If no new rocks formed at mid ocean ridges and volcanoes, the earth would just be covered with dust.
The number one agent of this mechanical break down of rocks is water, and the fact that we are on the water planet goes a long way towards explaining why we have all this erosion going on all the time. Water can carry scouring particles, which grind away on the surface of bed rock, and dissolve soluble minerals in the crystalline matrix of rocks, weakening them. Water can physically undermine rock structures, and waves can transmit hundreds if not thousands of pounds of pressure per square foot upon impact. And this is all liquid water, frozen water in the form of glaciers, is responsible for huge amounts of erosion over entire landscape regions. On a smaller scale, the freeze and thaw cycle of physical weathering, where liquid water seeps into cracks in rocks, and then expands as it freezes, splitting the rock open, is responsible for much of the break down of the granite we have here in Maine. In fact, here in Maine, between the recent glaciation and the freeze thaw cycles that are inevitable in winter, most of the erosion of rock we see around us is physical.
Equally, if not more important world wide is the process of chemical weathering. The chemical weathering of rocks results mainly from weak acids that form in water. This is primarily carbonic acid, which results from the carbon dioxide naturally found in the atmosphere mixing with surface water. Chemical weathering tends to run faster in warm humid environments, (one reason we have less of it occurring here). In chemical weathering the particles of rock tend to get smaller, just like in mechanical weathering, but they also often are changed chemically as well. The residual minerals that result from chemical weathering are often forms of clay, which as a former amateur potter I find very interesting. And while we have lots of clay here in Maine, it is formed from a totally different process, and isn’t at all related to the clay we get from the southern US, clay that results from the chemical weathering of rocks.
We’ve all heard the expression “rust never sleeps”, well, erosion doesn’t either. We will talk more about erosion in the coming weeks, but in the mean time understand that the forces of mountain building and erosion are in a tenuous balance, the landscape we see around us at any given time is a snap shot of the tension between these two forces. Orogeny and erosion teeter totter back and forth over millions of years, but without them both, the world would be a very different looking place.
References:
The business: From Prof. Stephen Nelson at Tulane University, from an introductory Earth Science class: http://www.tulane.edu/~sanelson/geol111/weathering.htm
The movement of the plates that makeup the earth’s crust causes earthquakes, yields volcanoes and ultimately results in orogeny, or the uplift of mountains. In the story we tell ourselves about the world, these forces are cast in dramatic roles (whether or not they really deserve them is for a different day). Volcanoes and earth quakes are exciting (if also dangerous), mountains soar above us, the alpine realm virtually synonymous with adventure. Today though, we turn away from these easy to tell tales, to explore the other side of the coin. Remember, in the universe for every action, there is an equal and opposite reaction. And while we are easily distracted and entertained by the expansive spectacle of orogeny, you need to be aware that there is another force at work in the universe. A subversive force, one that constantly and endlessly eats away at the world as we know it, seeking equilibrium. This leveling energy is most commonly known and experienced as erosion.
In physics there is a concept called entropy, which states that systems will tend from states of order to states of disorder, if isolated from additional inputs that would decrease the disorder. Basically put—without input of energy, things gradually fall apart. One way to define a living being is that it is anti entropy, by being alive the life form is using a constant input of energy to combat the tendency towards disorder of its molecules and atoms. Death is when entropy finally wins.
Erosion is entropy in the geologic frame of reference. Mountains may rise up, rocks may form bed rock, but little by little they will be broken down and, given enough time, flattened and brought back down to earth. The mechanism of erosion is called weathering, and can happen either mechanically or chemically. The easiest one to think about is mechanical weathering, we all understand about the physical break down of material. Big rocks turn into small rocks, small rocks turn into pebbles, pebbles turn into sand, sand turns into…well you get the idea. If no new rocks formed at mid ocean ridges and volcanoes, the earth would just be covered with dust.
The number one agent of this mechanical break down of rocks is water, and the fact that we are on the water planet goes a long way towards explaining why we have all this erosion going on all the time. Water can carry scouring particles, which grind away on the surface of bed rock, and dissolve soluble minerals in the crystalline matrix of rocks, weakening them. Water can physically undermine rock structures, and waves can transmit hundreds if not thousands of pounds of pressure per square foot upon impact. And this is all liquid water, frozen water in the form of glaciers, is responsible for huge amounts of erosion over entire landscape regions. On a smaller scale, the freeze and thaw cycle of physical weathering, where liquid water seeps into cracks in rocks, and then expands as it freezes, splitting the rock open, is responsible for much of the break down of the granite we have here in Maine. In fact, here in Maine, between the recent glaciation and the freeze thaw cycles that are inevitable in winter, most of the erosion of rock we see around us is physical.
Equally, if not more important world wide is the process of chemical weathering. The chemical weathering of rocks results mainly from weak acids that form in water. This is primarily carbonic acid, which results from the carbon dioxide naturally found in the atmosphere mixing with surface water. Chemical weathering tends to run faster in warm humid environments, (one reason we have less of it occurring here). In chemical weathering the particles of rock tend to get smaller, just like in mechanical weathering, but they also often are changed chemically as well. The residual minerals that result from chemical weathering are often forms of clay, which as a former amateur potter I find very interesting. And while we have lots of clay here in Maine, it is formed from a totally different process, and isn’t at all related to the clay we get from the southern US, clay that results from the chemical weathering of rocks.
We’ve all heard the expression “rust never sleeps”, well, erosion doesn’t either. We will talk more about erosion in the coming weeks, but in the mean time understand that the forces of mountain building and erosion are in a tenuous balance, the landscape we see around us at any given time is a snap shot of the tension between these two forces. Orogeny and erosion teeter totter back and forth over millions of years, but without them both, the world would be a very different looking place.
References:
The business: From Prof. Stephen Nelson at Tulane University, from an introductory Earth Science class: http://www.tulane.edu/~sanelson/geol111/weathering.htm
Plate Tectonics and You!
Note: This program first aired on February 2, 2013.
Imagine if we could peel the Earth like we peel an orange. The outer skin of the earth is made up of rigid plates of rock. These plates fit together in a spherical puzzle, just like the pieces of orange skin, if we were nimble fingered enough to put them back together. The spherical puzzle is where the Earth as orange analogy ends however, because the plates that make up the surface of the earth are constantly remaking themselves, changing shape and moving around, in ways the skin of an orange can only dream of.
The study of these plates and their movement is the field of plate tectonics, a branch of science that didn’t even exist until the mid 20th century, though the recognition that the landmasses of the Earth, while separated by oceans, seemed to fit together existed as soon as the world was mapped.
Plate tectonics works because of the anatomy of the Earth. The outer most layer of the Earth is called the crust, and is composed mainly of silica, oxygen and a few heavier elements like iron and magnesium, in the forms of granitic and basaltic rocks. The crust is relatively light, having a lower density than the underlying rocks that make up the deeper tissues of the Earth, the mantle and the core. The rocks directly below the crust are rocks by chemistry only, behaving more like silly putty than the solid bedrock we are familiar with. The light crust literally floats on the denser material below, and because that material is somewhat plastic, it deforms when force is applied to it, and flows slowly, much like a glacier flows, seemingly solid, but constantly moving.
Just like the pieces of peel from an orange, the crust of the earth is broken into discrete chunks, or plates. They slowly drift around on the surface of our sphere, grinding past each other causing earth quakes, smashing into each other causing mountains to rise up where none were before, and diving back down into the hot depths of the inner Earth, where they are heated and melt and eventually rise back towards the surface as the material of volcanoes. Understanding the movement of the plates has provided humanity with an elegant and overarching set of explanations for many of the shapes and forms we see on the landscape around us every day.
What we think of as permanent and unchanging space is really a dynamic mosaic, albeit one that changes at a pace we cannot comprehend. The cleverer of us have learned to read the signs of that slow motion dance on the land, while the rest of us persist in our dream that what we see around us is what has always been, and what will always be.
References:
I don’t generally direct people to Wikipedia (primarily and admittedly due to my own academic snobbery), but in this case, the Plate Tectonics entry is actually quite well done http://en.wikipedia.org/wiki/Plate_tectonics.
Those folks at UC Berkley have done it again…animations! Interactive maps! http://www.ucmp.berkeley.edu/geology/tectonics.html
Here’s a lot more info from the University of Texas at Arlington—including plate tectonics stuff you can put on your Ipad, http://www.scotese.com/
Imagine if we could peel the Earth like we peel an orange. The outer skin of the earth is made up of rigid plates of rock. These plates fit together in a spherical puzzle, just like the pieces of orange skin, if we were nimble fingered enough to put them back together. The spherical puzzle is where the Earth as orange analogy ends however, because the plates that make up the surface of the earth are constantly remaking themselves, changing shape and moving around, in ways the skin of an orange can only dream of.
The study of these plates and their movement is the field of plate tectonics, a branch of science that didn’t even exist until the mid 20th century, though the recognition that the landmasses of the Earth, while separated by oceans, seemed to fit together existed as soon as the world was mapped.
Plate tectonics works because of the anatomy of the Earth. The outer most layer of the Earth is called the crust, and is composed mainly of silica, oxygen and a few heavier elements like iron and magnesium, in the forms of granitic and basaltic rocks. The crust is relatively light, having a lower density than the underlying rocks that make up the deeper tissues of the Earth, the mantle and the core. The rocks directly below the crust are rocks by chemistry only, behaving more like silly putty than the solid bedrock we are familiar with. The light crust literally floats on the denser material below, and because that material is somewhat plastic, it deforms when force is applied to it, and flows slowly, much like a glacier flows, seemingly solid, but constantly moving.
Just like the pieces of peel from an orange, the crust of the earth is broken into discrete chunks, or plates. They slowly drift around on the surface of our sphere, grinding past each other causing earth quakes, smashing into each other causing mountains to rise up where none were before, and diving back down into the hot depths of the inner Earth, where they are heated and melt and eventually rise back towards the surface as the material of volcanoes. Understanding the movement of the plates has provided humanity with an elegant and overarching set of explanations for many of the shapes and forms we see on the landscape around us every day.
What we think of as permanent and unchanging space is really a dynamic mosaic, albeit one that changes at a pace we cannot comprehend. The cleverer of us have learned to read the signs of that slow motion dance on the land, while the rest of us persist in our dream that what we see around us is what has always been, and what will always be.
References:
I don’t generally direct people to Wikipedia (primarily and admittedly due to my own academic snobbery), but in this case, the Plate Tectonics entry is actually quite well done http://en.wikipedia.org/wiki/Plate_tectonics.
Those folks at UC Berkley have done it again…animations! Interactive maps! http://www.ucmp.berkeley.edu/geology/tectonics.html
Here’s a lot more info from the University of Texas at Arlington—including plate tectonics stuff you can put on your Ipad, http://www.scotese.com/
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