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
Saturday, February 23, 2013
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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