Note: This program first aired on June 29, 2013.
The other morning I got a phone call. It was my niece, saying, “Sarah, Sarah, I found a baby bird on the lawn! I watched it for twenty minutes and it is still there, can I keep it for a day?” I told her to leave it where it was, and that I would be right over. When I arrived we found not one but two baby chipping sparrows, staying quite still in the grass, minding their own business, and two adult chipping sparrows, noisily and nervously flitting about in the trees above. The date was June 14, what many Americans celebrate as Flag Day; for me now it will always be Fledging Day.
Merriam Webster defines fledge, the verb, as “to acquire the feathers necessary for flight or independent activity, also to leave the nest after acquiring such feathers”. The word can also be used as a transitive verb, which simply means it has an object, as in “to rear until ready for flight” or, my favorite, “to cover with or as if with feathers or down”. The definitions make me feel that it is as much about getting the feathers as it is about leaving the nest, which may be, because you can’t leave the nest until you have the feathers.
The little chipping sparrows we found were in fact fledglings, young birds who, under the care of their parents, having grown sufficient feathers, made the leap from the nest into the big world beyond. These sparrows, like most small song birds, are what is called altricial at hatching, meaning they are tiny, without feathers and with eyes closed. They can’t keep themselves warm, and are dependent on their parents for everything. They look like little fetuses, which is essentially what they are. They will live in the nest for days to weeks as they grow, for example, those chipping sparrows were in the nest for about 10 days before they fledged. The rate at which these babies develop is quite amazing, it seems like you could literally watch them grow. For altricial birds, fledging means growing enough feathers to leave the nest, not necessarily having the ability of full flight.
On the other end of the baby bird spectrum (and it is a spectrum) are birds who are precocial at birth, meaning they have feathers, open eyes and are capable of movement when they hatch, and may or may not feed them selves from the start. Ducks and other shore and water birds exemplify this pattern. The babies may not be able to fly immediately, but often they can swim. For precocial birds, they have fledged when they can actually fly.
It is curious that there is such a difference in the stage of development of baby birds when they are born. This difference is a result of evolution. Nature has presented a problem to birds everywhere, namely “How do we keep our vulnerable young from getting eaten by some hungry predator?” (truly, the problem that faces all parents in the world). For birds, evolution has produced two quite elegant solutions, based on resource availability, and with pros and cons to each. Song birds migrate great distances to come to habitat with sufficient food resources and nesting areas. They have evolved to put their energy into simply getting here and getting down to the business of mating as soon as possible. Energetically that means that they put relatively little into their eggs, and the less you put into an egg, the less you are going to get out of it, hence the helpless altricial young. They are able to invest less bodily energy into egg production because once the young are born, they are able to collect plenty of food to feed them; the parents’ investment is on the outside of the egg shell. This is still a dangerous strategy, though, as finding a nest full of baby birds is like winning the lottery for a predator. It’s a concentrated source of nutrition, those tasty little niblets are all in one handy spot, the nest. Hence the speed with which these babies grow. Evolution has favored the fastest periods of in nest development, because the whole time they are in the nest, those baby birds are easy targets.
Precocial birds eliminate the possibility of having all of the young eaten in one predator attack, by dispersing them from the nest as soon as possible, mainly, as soon as they hatch. Individually they may be picked off, but they won’t all go together in a big gulp. The trade off for this in the physiological preparation of the parents. Their investment, particularly that of the mother, is on the front end of the nesting process; she must eat enough while developing the eggs to create a big fat juicy yolk laden egg. An egg like that contains enough nutrition to grow a baby bird that has feathers and run around as soon as it hatches. This strategy works really well, but obtaining that kind of nutrition on the front end is clearly not an option for many kinds of birds. The process of evolution has guided different bird species in different circumstances in different directions, and hatchling development is a perfect example of this. Happy Fledging Day everyone!
References:
Richard Sibly, et al, Energetics. Lifestyle and reproduction in birds PNAS, April 24, 2012 http://www.pnas.org/content/early/2012/05/17/1206512109.full.pdf
Mary Holland Naturally Curious 2010, Trafalgar Square Books—This fantastic book is also a popular blog and an email list serve: http://naturallycuriouswithmaryholland.wordpress.com/
Paul Ehrlich et al, The Birder’s Handbook: A field guide to the natural history of north American birds, 1988, Simon and Schuster. A classic, with detailed species accounts and a wide array of content essays.
One of the most comprehensive bird websites out there, from the Ornithology Lab at Cornell University http://www.birds.cornell.edu
The information about the evolutionary strategies of precocial vs. altricial young came from the Stanford University bird website: http://www.stanford.edu/group/stanfordbirds/text/essays/Precocial_and_Altricial.html They seem to have an active on campus birding community.
Sunday, July 7, 2013
Saturday, June 22, 2013
A Robin's Life Work
Note: This program first aired June 22, 2013.
I’ve had the pleasure of watching a pair of robins nesting this spring. For the past several years, they have taken to nesting on human made structures around an outbuilding at my house; on window ledges, on top of propped up ladders, on exposed beams. I’ve watched them in the past, but I’m ashamed to say that I didn’t really pay attention to them, due to a mix of caution and frank snobbery. Part of me didn’t want to disturb them, and part of me thought “oh, well, they are just robins. Robins are everywhere, they are so common, there’s nothing special about them.” This is a trap that naturalists everywhere fall into, we want to spot the rare bird, be the first to find the unusual flower, identify the large mammal tracks. So caught up are we with the excitement of the uncommon that we become blind to the more ordinary friends we see around us on a daily basis; the dandelion, the daisy, the sparrow, the robin.
This year I let go of my pretension. I was in a class, and one of our assignments was to watch a bird for an hour and record our observations. Because I am both an over achiever and an over scheduler, I needed to find an easy bird to observe, something close to home, something predictable, something like a robin nesting on a window ledge right out my front door. I decided that an hour was clearly not long enough, I would watch them during their entire nesting cycle, and document what I saw (that’s the over achieving part). What I learned is that every creature, every organism, every entity out there has something to teach us, if we are willing and open to learn it.
Several weeks ago, the robins began building their nest; The female builds the nest, with help from her mate. I didn’t know that from watching, a little back ground reading never hurt anyone. The pair struggled to construct the nest out of dry grass during high winds. It seemed futile to me. Then it rained, the ground became wet, mud formed. Robins construct a substantial part of their nests from mud, and these robins didn’t make any progress on their nest building until spring weather favored them with some building material. Suddenly, from what looked like a sloppy pile of mud on a window sill, a beautiful grass lined nest was formed. Next the female seemed to be testing out the nest, sitting in it some times leaving it other times. I realized she was preparing to lay eggs. One day I saw an egg in the nest, and worried that she had abandoned it, as she was not there every time I looked. Again, just as suddenly there were four eggs in the nest, and she was sitting consistently. Robins, like many birds will delay the incubation until all the eggs in her clutch are laid, so they all hatch at the same time. Her spotty attendance to the nest was what I was observing, by not sitting on the eggs she was keeping them cool so they wouldn’t start to develop.
The book said that the eggs would hatch in 12 to 14 days, so I marked the range of due dates on my calendar. The first due day two eggs had hatched, the second day a third egg had hatched, and by the third day all four had hatched. That meant that the first two had a two day head start on the last hatchling, and I wondered how that would play out in nest dynamics. The book also said that they would fledge in 14 to 16 days, meaning they would grow from helpless pink featherless grubs to fully feathered birds in about two weeks. I couldn’t believe that, so I decided to photo document their growth, with a single picture each day. It turns out that a photo really is worth a thousand words. By day 12 the largest nestling had fledged. By day 13 the next one had. Today is day 14. I fully expect that by the end of today when I go out and look, the nest will be empty.
In watching these animals, who I am so grateful to for accommodating my curiosity, I was given a gift. I saw how fast those babies grew, and thought of all of my friends and their children, and my young niece and nephew. I watched the mother sit faithfully on the nest for two weeks, and then saw the father return to share feeding responsibilities with the mother once the eggs had hatched. I was aware of the parents’ alarm when I would approach the nest for my lightening fast once daily photo, observing how the young would immediately lower themselves in the nest in response to their parents’ calls. When darkness fell each night, I would imagine the mother robin, sitting on her nest in the dark, with only her self between her babies and the unknown and hungry night beyond. Raising those babies is truly a robin’s life work. What kind of person am I if I am not awed by that?
As we enter this period of summer’s bounty and ease, pick something, anything, anything you will see on a daily basis, don’t wait for the Blackburnian warbler or the rose pogonia. Watch it until it brings you to your knees. I promise you, your life will be richer for it.
References:
The Birder’s Handbook Paul Ehrlich et al, 1988 Simon and Schuster, the Bible for concise go to info about North American bird natural history.
Nice little website about robins, including opportunities for citizen science. http://www.learner.org/jnorth/tm/robin/EggstraEggstra.html
I’ve had the pleasure of watching a pair of robins nesting this spring. For the past several years, they have taken to nesting on human made structures around an outbuilding at my house; on window ledges, on top of propped up ladders, on exposed beams. I’ve watched them in the past, but I’m ashamed to say that I didn’t really pay attention to them, due to a mix of caution and frank snobbery. Part of me didn’t want to disturb them, and part of me thought “oh, well, they are just robins. Robins are everywhere, they are so common, there’s nothing special about them.” This is a trap that naturalists everywhere fall into, we want to spot the rare bird, be the first to find the unusual flower, identify the large mammal tracks. So caught up are we with the excitement of the uncommon that we become blind to the more ordinary friends we see around us on a daily basis; the dandelion, the daisy, the sparrow, the robin.
This year I let go of my pretension. I was in a class, and one of our assignments was to watch a bird for an hour and record our observations. Because I am both an over achiever and an over scheduler, I needed to find an easy bird to observe, something close to home, something predictable, something like a robin nesting on a window ledge right out my front door. I decided that an hour was clearly not long enough, I would watch them during their entire nesting cycle, and document what I saw (that’s the over achieving part). What I learned is that every creature, every organism, every entity out there has something to teach us, if we are willing and open to learn it.
Several weeks ago, the robins began building their nest; The female builds the nest, with help from her mate. I didn’t know that from watching, a little back ground reading never hurt anyone. The pair struggled to construct the nest out of dry grass during high winds. It seemed futile to me. Then it rained, the ground became wet, mud formed. Robins construct a substantial part of their nests from mud, and these robins didn’t make any progress on their nest building until spring weather favored them with some building material. Suddenly, from what looked like a sloppy pile of mud on a window sill, a beautiful grass lined nest was formed. Next the female seemed to be testing out the nest, sitting in it some times leaving it other times. I realized she was preparing to lay eggs. One day I saw an egg in the nest, and worried that she had abandoned it, as she was not there every time I looked. Again, just as suddenly there were four eggs in the nest, and she was sitting consistently. Robins, like many birds will delay the incubation until all the eggs in her clutch are laid, so they all hatch at the same time. Her spotty attendance to the nest was what I was observing, by not sitting on the eggs she was keeping them cool so they wouldn’t start to develop.
The book said that the eggs would hatch in 12 to 14 days, so I marked the range of due dates on my calendar. The first due day two eggs had hatched, the second day a third egg had hatched, and by the third day all four had hatched. That meant that the first two had a two day head start on the last hatchling, and I wondered how that would play out in nest dynamics. The book also said that they would fledge in 14 to 16 days, meaning they would grow from helpless pink featherless grubs to fully feathered birds in about two weeks. I couldn’t believe that, so I decided to photo document their growth, with a single picture each day. It turns out that a photo really is worth a thousand words. By day 12 the largest nestling had fledged. By day 13 the next one had. Today is day 14. I fully expect that by the end of today when I go out and look, the nest will be empty.
In watching these animals, who I am so grateful to for accommodating my curiosity, I was given a gift. I saw how fast those babies grew, and thought of all of my friends and their children, and my young niece and nephew. I watched the mother sit faithfully on the nest for two weeks, and then saw the father return to share feeding responsibilities with the mother once the eggs had hatched. I was aware of the parents’ alarm when I would approach the nest for my lightening fast once daily photo, observing how the young would immediately lower themselves in the nest in response to their parents’ calls. When darkness fell each night, I would imagine the mother robin, sitting on her nest in the dark, with only her self between her babies and the unknown and hungry night beyond. Raising those babies is truly a robin’s life work. What kind of person am I if I am not awed by that?
As we enter this period of summer’s bounty and ease, pick something, anything, anything you will see on a daily basis, don’t wait for the Blackburnian warbler or the rose pogonia. Watch it until it brings you to your knees. I promise you, your life will be richer for it.
References:
The Birder’s Handbook Paul Ehrlich et al, 1988 Simon and Schuster, the Bible for concise go to info about North American bird natural history.
Nice little website about robins, including opportunities for citizen science. http://www.learner.org/jnorth/tm/robin/EggstraEggstra.html
Wednesday, June 19, 2013
The History of Maine Part 12: Humans and the Future of Maine
Note: This program first aired on June 15, 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’ve reached the end of this series with a look the general trends of the human impacts on the Maine landscape.
If we had to summarize what happened to Maine as a result of human impact we could summarize it thusly: forest, farm forest. As we have said previously, the post glacial biotic community here is forest, at least in the current climatic regime. That is no surprise, follow the 45th parallel around the globe and what you will find is temperate forest world wide. The composition of that forest has changed over the past 12,000 years, but in the face of any disturbance, trees are what grow back here. We can consider European settlers as a major disturbance to this forest community, their direct impact peaked in the late 19th century, that is the “farm” part of the forest, farm, forest pattern. Since that time for a number of social and economic reasons, the forests have returned (not that they ever actually went that far in the first place).
European settlers first arrived in Maine in the early 17th century and for nearly 150 years enjoyed a precarious existence, eeking out a living tied to the coast line and coastal rivers and estuaries and warring with each other, and with the native population, which had been decimated soon after the Europeans arrived by European pathogens. By 1670 a whopping 3500 English settlers lived along the coast and coastal rivers, west of Penobscot Bay, with additional French settlers to its east. The low population numbers and the instability caused by constant conflict kept the impact of these new human colonists fairly low. Deforestation was strongly limited to the immediate coast, and up river valleys, and consisted of clearing for subsistence agriculture, and targeted harvesting of oak for barrels and white pines for ship masts.
Here is where geopolitics influences ecology. Once the American Revolution settled things and relative stability spread across the area, the population of “not yet Maine” grew dramatically. With this population increase came significant increases in land clearing and forest harvesting. It is important to take a moment and parse out these various levels of human impact. Land cleared for agriculture could be one of three things; land cleared for pasturing grazing animals, land cleared for hay fields and land cleared for tillage and the planting of crops. At its peak in the late 19th century, Maine was as much as 15% cleared for these uses (a number that has only gone back down from that time). Cutting in the forest was targeted at white pine for lumber, hemlock for the tanneries, oaks for barrels and ship building, and other hard woods for fuel wood, for both Maine and the Boston market. Forestry at that time was targeted, clear cutting was not part of the system, and wouldn’t be until the late 20th century.
This boom continued in the 19th century, until the time of the civil war and just after. At that point farms began to be abandoned with amazing speed, as the rail roads opened up the mid west (and their deep rich more easily farmed soils) and the economic center of gravity in America shifted from the Northeast westward. Forestry changed as well, as the best lumber logs became harder and harder to find, it was only the advent of the pulp and paper industry in the late 1800’s that kept the forest industry alive in the state. So Maine, the pine tree state, achieved its cleared land maximum just after the civil war, and has been growing trees back ever since. Even the spruce bud worm out break of the 1970’s and the change to industrial land ownership and subsequent clear cutting in the second half of the 20th century have not managed to change the undeniable fact, in Maine, if you turn your back, a tree will sprout. It was only through constant back breaking vigilance that Maine was as cleared as it was in the mid 19th century.
Will it always be so? I doubt it. If there is one constant on Earth it is change. Now our actions will be influencing the Maine landscape well beyond clearing for agriculture or cutting trees in the forest. As climate changes in the coming decades, I doubt that Maine will become a treeless landscape, but a thousand years from now? Who knows? The biotic community we see around us is a result of the average temperature and the amount of water that falls from the sky, both factors that stand to be significantly altered by changing climate. So it seems that the tale of humans’ impact on the Maine landscape isn’t finished after all.
And thus concludes our look into the deep history of the Maine landscape. The tale may not be done, but this series is. Keep your eyes open and read the signs in your own neighborhood. You will be amazed, as I have been, where that story takes you.
References:
If this kind of history floats your boat, I can’t recommend this book enough: Andrew Barton and friends The Changing Nature of the Maine Woods. Readable and excellent!
A classic: William Cronin’s Changes in the Land. This one looks at the impact of Native Americans on the primeval forest, and is definitely weighted more towards southern New England. Lots of good information though.
Colin Woodard’s The Lobster Coast provides a comprehensive overview of the history of the people in Maine, particularly along the coast. Though “lobster” is the unifying theme, there is a tremendous amount of environmental history is this book. Very readable, super interesting.
Curious about the future? Check out this report from the UMaine Climate Change Institute: “ Maine’s Climae Future” http://climatechange.umaine.edu/files/Maines_Climate_Future.pdf
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’ve reached the end of this series with a look the general trends of the human impacts on the Maine landscape.
If we had to summarize what happened to Maine as a result of human impact we could summarize it thusly: forest, farm forest. As we have said previously, the post glacial biotic community here is forest, at least in the current climatic regime. That is no surprise, follow the 45th parallel around the globe and what you will find is temperate forest world wide. The composition of that forest has changed over the past 12,000 years, but in the face of any disturbance, trees are what grow back here. We can consider European settlers as a major disturbance to this forest community, their direct impact peaked in the late 19th century, that is the “farm” part of the forest, farm, forest pattern. Since that time for a number of social and economic reasons, the forests have returned (not that they ever actually went that far in the first place).
European settlers first arrived in Maine in the early 17th century and for nearly 150 years enjoyed a precarious existence, eeking out a living tied to the coast line and coastal rivers and estuaries and warring with each other, and with the native population, which had been decimated soon after the Europeans arrived by European pathogens. By 1670 a whopping 3500 English settlers lived along the coast and coastal rivers, west of Penobscot Bay, with additional French settlers to its east. The low population numbers and the instability caused by constant conflict kept the impact of these new human colonists fairly low. Deforestation was strongly limited to the immediate coast, and up river valleys, and consisted of clearing for subsistence agriculture, and targeted harvesting of oak for barrels and white pines for ship masts.
Here is where geopolitics influences ecology. Once the American Revolution settled things and relative stability spread across the area, the population of “not yet Maine” grew dramatically. With this population increase came significant increases in land clearing and forest harvesting. It is important to take a moment and parse out these various levels of human impact. Land cleared for agriculture could be one of three things; land cleared for pasturing grazing animals, land cleared for hay fields and land cleared for tillage and the planting of crops. At its peak in the late 19th century, Maine was as much as 15% cleared for these uses (a number that has only gone back down from that time). Cutting in the forest was targeted at white pine for lumber, hemlock for the tanneries, oaks for barrels and ship building, and other hard woods for fuel wood, for both Maine and the Boston market. Forestry at that time was targeted, clear cutting was not part of the system, and wouldn’t be until the late 20th century.
This boom continued in the 19th century, until the time of the civil war and just after. At that point farms began to be abandoned with amazing speed, as the rail roads opened up the mid west (and their deep rich more easily farmed soils) and the economic center of gravity in America shifted from the Northeast westward. Forestry changed as well, as the best lumber logs became harder and harder to find, it was only the advent of the pulp and paper industry in the late 1800’s that kept the forest industry alive in the state. So Maine, the pine tree state, achieved its cleared land maximum just after the civil war, and has been growing trees back ever since. Even the spruce bud worm out break of the 1970’s and the change to industrial land ownership and subsequent clear cutting in the second half of the 20th century have not managed to change the undeniable fact, in Maine, if you turn your back, a tree will sprout. It was only through constant back breaking vigilance that Maine was as cleared as it was in the mid 19th century.
Will it always be so? I doubt it. If there is one constant on Earth it is change. Now our actions will be influencing the Maine landscape well beyond clearing for agriculture or cutting trees in the forest. As climate changes in the coming decades, I doubt that Maine will become a treeless landscape, but a thousand years from now? Who knows? The biotic community we see around us is a result of the average temperature and the amount of water that falls from the sky, both factors that stand to be significantly altered by changing climate. So it seems that the tale of humans’ impact on the Maine landscape isn’t finished after all.
And thus concludes our look into the deep history of the Maine landscape. The tale may not be done, but this series is. Keep your eyes open and read the signs in your own neighborhood. You will be amazed, as I have been, where that story takes you.
References:
If this kind of history floats your boat, I can’t recommend this book enough: Andrew Barton and friends The Changing Nature of the Maine Woods. Readable and excellent!
A classic: William Cronin’s Changes in the Land. This one looks at the impact of Native Americans on the primeval forest, and is definitely weighted more towards southern New England. Lots of good information though.
Colin Woodard’s The Lobster Coast provides a comprehensive overview of the history of the people in Maine, particularly along the coast. Though “lobster” is the unifying theme, there is a tremendous amount of environmental history is this book. Very readable, super interesting.
Curious about the future? Check out this report from the UMaine Climate Change Institute: “ Maine’s Climae Future” http://climatechange.umaine.edu/files/Maines_Climate_Future.pdf
The History of Maine: Part 11 First Humans in Maine
Note: This program first aired on June 1, 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’ve reached the third and final (for now) chapter in Maine’s deep history, and it is one we all have a hand in. Before we dive in though, lets quickly recap first two aspects of the existence of the Maine landscape.
About 600 million years ago the very faintest hints of the beginning of Maine were in the air. As a result of the constant movement of the Earth’s tectonic plates, coastal sediments were accreted on to the edge of the North American plate, and volcanic activity added new igneous rock to the mix as well, both above and below the surface. Additionally, little bits of continental plate that likely originated on the ancient European continent also became plastered to the edge of North America. By bits and pieces, the crust of Maine was formed. Two million years ago, the northern hemisphere entered an ice age, and continental glacier after continental glacier advanced over the Maine landscape, scouring and smoothing, and dumping the rocky sediment that challenges gardeners throughout the state.
The last glacier retreated from the state between 15,000 and 13,000 years ago, and the Maine landscape was likely recolonized with Arctic tundra plants, which were then rapidly outcompeted by a forest community as climate continued to warm. Paleopollen analysis indicates that the post glacial environment was mainly forested (with a variety of community compositions). So the types and sizes of trees may have been somewhat different, but after the glaciers left, Maine didn’t look shockingly different than it does today, at least to the casual observer. Botanists and foresters may argue this point, but I think it is important to understand that in the big picture, Maine is solidly a forest community.
It is likely that as soon as there was large game in the post glacial forest, people were here as well. There is archeological evidence to support this. And while there were multiple native cultures that flourished at various times during this post glacial epoch, current thinking posits that the native populations here had a relatively low population density (relative to southern New England or the southeast US), due to an almost entirely hunter gatherer lifestyle. Agriculture was used in more southern regions, and in far southern Maine, but not in the majority of the state. So, early native populations had some kind of impact on the Maine environment, but it was strongly limited by the low population density and lifestyle. Geographically, evidence suggests that the native populations were concentrated on the coast, so for vast stretches of Maine, while there may have been human activity in the past 10,000 years, it left little impact.
In terms of human impact, European colonization was the turning point. It began in earnest in 1607 with the failed Popham colony, and the various French and English 17th century trading and fishing outposts. These early developments were entirely coastal, as transportation was water based. Just think about that for a moment. There were no roads, just overland foot paths. If you wanted to get anywhere you got in a boat. Think about how access to transportation, in this case, the water, must have guided settlement, and in fact, limited it to the thinnest of strips right along coastal waterways and eventually, up major rivers as well. European’s ties to the water, as well as conflict with the native populations kept the majority of human impact along the coast for nearly 200 years.
We’ll look at what happened next, next week, when we finish the chapter of the human influence on the Maine landscape, and perhaps even peer into the future.
References:
Terrific new book by Andrew Barton and friends The Changing Nature of the Maine Woods. Readable and excellent!
A classic: William Cronin’s Changes in the Land. This one looks at the impact of Native Americans on the primeval forest, and is definitely weighted more towards southern New England. Lots of good information though.
Recently Maine Public Broadcasting did an interesting call in show about the first people in Maine. Listen to it here: http://www.mpbn.net/OnDemand/AudioOnDemand/MaineCalling/tabid/288/ctl/ViewItem/mid/3682/ItemId/28278/Default.aspx
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’ve reached the third and final (for now) chapter in Maine’s deep history, and it is one we all have a hand in. Before we dive in though, lets quickly recap first two aspects of the existence of the Maine landscape.
About 600 million years ago the very faintest hints of the beginning of Maine were in the air. As a result of the constant movement of the Earth’s tectonic plates, coastal sediments were accreted on to the edge of the North American plate, and volcanic activity added new igneous rock to the mix as well, both above and below the surface. Additionally, little bits of continental plate that likely originated on the ancient European continent also became plastered to the edge of North America. By bits and pieces, the crust of Maine was formed. Two million years ago, the northern hemisphere entered an ice age, and continental glacier after continental glacier advanced over the Maine landscape, scouring and smoothing, and dumping the rocky sediment that challenges gardeners throughout the state.
The last glacier retreated from the state between 15,000 and 13,000 years ago, and the Maine landscape was likely recolonized with Arctic tundra plants, which were then rapidly outcompeted by a forest community as climate continued to warm. Paleopollen analysis indicates that the post glacial environment was mainly forested (with a variety of community compositions). So the types and sizes of trees may have been somewhat different, but after the glaciers left, Maine didn’t look shockingly different than it does today, at least to the casual observer. Botanists and foresters may argue this point, but I think it is important to understand that in the big picture, Maine is solidly a forest community.
In terms of human impact, European colonization was the turning point. It began in earnest in 1607 with the failed Popham colony, and the various French and English 17th century trading and fishing outposts. These early developments were entirely coastal, as transportation was water based. Just think about that for a moment. There were no roads, just overland foot paths. If you wanted to get anywhere you got in a boat. Think about how access to transportation, in this case, the water, must have guided settlement, and in fact, limited it to the thinnest of strips right along coastal waterways and eventually, up major rivers as well. European’s ties to the water, as well as conflict with the native populations kept the majority of human impact along the coast for nearly 200 years.
We’ll look at what happened next, next week, when we finish the chapter of the human influence on the Maine landscape, and perhaps even peer into the future.
References:
Terrific new book by Andrew Barton and friends The Changing Nature of the Maine Woods. Readable and excellent!
A classic: William Cronin’s Changes in the Land. This one looks at the impact of Native Americans on the primeval forest, and is definitely weighted more towards southern New England. Lots of good information though.
Recently Maine Public Broadcasting did an interesting call in show about the first people in Maine. Listen to it here: http://www.mpbn.net/OnDemand/AudioOnDemand/MaineCalling/tabid/288/ctl/ViewItem/mid/3682/ItemId/28278/Default.aspx
Monday, May 27, 2013
The History of Maine Part 10: Sea Level and the Coastline
Note: This program first aired on May 25, 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 looking at some of the landscape features the glaciers left as they retreated 13,000 years ago here in Maine. That period of deglaciation had another profound impact on the Maine landscape, particularly the one most people know Maine for: the coast.
When we look at the location of the coast line, we are really looking at the edge of the water relative to the elevation of the landscape. If the landform is low, the water can move in, if the land form is high, the water is pushed out. There are two factors here that can change, the amount or volume of the water (the more water there is, the more three dimensional space it takes up, the higher it rises relative to the land, if all things are equal), and the level of the land (this is trickier to get your head around, but just remember that the crust of the Earth is floating, just like a ship at sea—the heavier the boat, the lower it floats. Solid crust floats on the more plastic layers of the Earth below.)
When we look at these two things relative to glaciation, we see the complicated and variable history of Maine’s coastline in the past 13,000 years. When glaciers form, they form from water, generally liquid water that evaporates into the atmosphere and then falls back to Earth in solid form. Where does all that liquid come from? The ocean, so overall we see a drop in global sea level when large continental glaciers form, because so much liquid water is taken up out of the ocean. At the height of the last glacial advance, it is thought that sea levels in our neck of the woods were 300 to 400 feet lower than today as a result of this (a level that would have easily exposed the continental shelf, had it not been covered by ice).
The amount of water isn’t the only thing that can change however, remember, the actual relative level of the land can as well. Remember the ship I mentioned, when it is heavy is floats lower in the water, when it is empty it floats at a higher level. The crust that underlies the state of Maine is like that ship. And what could make the crust heavier than normal? How about 10,000 feet of solid ice? That would do it. The continental glacier was so large and massive, it caused the crust to become less buoyant and float a bit lower on the underlying mantle. The crust was literally depressed into the Earth. As a side note, this is happening today in Antarctica, much of that continent is actually below sea level as a result of the weight of its ice cap.
So that is how the stage was set when the last ice age began to end here in Maine, about 13,000ish years ago. Just like a trampoline with some one sitting on it, the Earth’s crust is deformed by the weight of the glacier, and there was less water in the ocean. That less water in the ocean bit was changing fast though, as the glacier was melting quite rapidly. All of that melt water returned to the ocean, which rose quite rapidly in response. And as the glacial melted, it relived the pressure on the underlying crust, and just like a trampoline when you bounce off it, the crust rebounded. These two events didn’t happen simultaneously though, the glacier melted a great deal faster than the Earth rebounded, which meant, the ocean water easily covered the newly exposed but still depressed landscape of Maine. This event is called the Marine Incursion and at its maximum the coastline was as far inland as Medway, near Baxter State Park. Soon though the Earth’s rebound caught up with the rising ocean, and then some (again, think of our trampoline; a bouncer gets pushed up above the equilibrium level before coming back down). At the height of the crust’s rebound, sea level was much lower than it is today, as the land rose up above the level of the ocean. During this period, about 11,000 years ago, much of the Gulf of Maine, in particular Georges Bank on the edge of the continental shelf, was dry land. Terrestrial fossils, including trees and mammoth tusks have been recovered from Georges Bank, and the Gulf of Maine was a shallow inland sea cut off from the Atlantic Ocean. Soon thereafter though, the rebound eased and even subsided a bit, and the rising ocean caught up. The present day coastline was more or less established in the last few thousand years, as the rapid changes that resulted from deglaciation ended and temporary equilibrium was restored.
Maine has what is called a drowned coastline, and I hope now you can see why. Next week we will look at the third major force that shapes the Maine landscape, us.
References:
D. W. Caldwell Roadside Geology of Maine 1998
Harry Thurston The Atlantic Coast: A Natural History 2011
David L. Kendall Glacier and Granite 1987
The Maine Geological Survey makes its surficial geology map available on line, in a printable 11x17 inch format. It has lots of good info on the results of the last glacial advance and retreat, and it’s free!
http://www.maine.gov/doc/nrimc/mgs/pubs/online/surficial/surficial11x17.pdf
Super nerds unite: check out the Maine Ice Age Trail, and you too can tour Hancock and Washington counties looking at gravel pits (I’ve done it, its awesome). http://iceagetrail.umaine.edu/ also includes an excellent overview of the last ice age in Maine http://iceagetrail.umaine.edu/content/iceageinmaine/iceageinmaine.php
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 looking at some of the landscape features the glaciers left as they retreated 13,000 years ago here in Maine. That period of deglaciation had another profound impact on the Maine landscape, particularly the one most people know Maine for: the coast.
When we look at the location of the coast line, we are really looking at the edge of the water relative to the elevation of the landscape. If the landform is low, the water can move in, if the land form is high, the water is pushed out. There are two factors here that can change, the amount or volume of the water (the more water there is, the more three dimensional space it takes up, the higher it rises relative to the land, if all things are equal), and the level of the land (this is trickier to get your head around, but just remember that the crust of the Earth is floating, just like a ship at sea—the heavier the boat, the lower it floats. Solid crust floats on the more plastic layers of the Earth below.)
When we look at these two things relative to glaciation, we see the complicated and variable history of Maine’s coastline in the past 13,000 years. When glaciers form, they form from water, generally liquid water that evaporates into the atmosphere and then falls back to Earth in solid form. Where does all that liquid come from? The ocean, so overall we see a drop in global sea level when large continental glaciers form, because so much liquid water is taken up out of the ocean. At the height of the last glacial advance, it is thought that sea levels in our neck of the woods were 300 to 400 feet lower than today as a result of this (a level that would have easily exposed the continental shelf, had it not been covered by ice).
The amount of water isn’t the only thing that can change however, remember, the actual relative level of the land can as well. Remember the ship I mentioned, when it is heavy is floats lower in the water, when it is empty it floats at a higher level. The crust that underlies the state of Maine is like that ship. And what could make the crust heavier than normal? How about 10,000 feet of solid ice? That would do it. The continental glacier was so large and massive, it caused the crust to become less buoyant and float a bit lower on the underlying mantle. The crust was literally depressed into the Earth. As a side note, this is happening today in Antarctica, much of that continent is actually below sea level as a result of the weight of its ice cap.
So that is how the stage was set when the last ice age began to end here in Maine, about 13,000ish years ago. Just like a trampoline with some one sitting on it, the Earth’s crust is deformed by the weight of the glacier, and there was less water in the ocean. That less water in the ocean bit was changing fast though, as the glacier was melting quite rapidly. All of that melt water returned to the ocean, which rose quite rapidly in response. And as the glacial melted, it relived the pressure on the underlying crust, and just like a trampoline when you bounce off it, the crust rebounded. These two events didn’t happen simultaneously though, the glacier melted a great deal faster than the Earth rebounded, which meant, the ocean water easily covered the newly exposed but still depressed landscape of Maine. This event is called the Marine Incursion and at its maximum the coastline was as far inland as Medway, near Baxter State Park. Soon though the Earth’s rebound caught up with the rising ocean, and then some (again, think of our trampoline; a bouncer gets pushed up above the equilibrium level before coming back down). At the height of the crust’s rebound, sea level was much lower than it is today, as the land rose up above the level of the ocean. During this period, about 11,000 years ago, much of the Gulf of Maine, in particular Georges Bank on the edge of the continental shelf, was dry land. Terrestrial fossils, including trees and mammoth tusks have been recovered from Georges Bank, and the Gulf of Maine was a shallow inland sea cut off from the Atlantic Ocean. Soon thereafter though, the rebound eased and even subsided a bit, and the rising ocean caught up. The present day coastline was more or less established in the last few thousand years, as the rapid changes that resulted from deglaciation ended and temporary equilibrium was restored.
Maine has what is called a drowned coastline, and I hope now you can see why. Next week we will look at the third major force that shapes the Maine landscape, us.
References:
D. W. Caldwell Roadside Geology of Maine 1998
Harry Thurston The Atlantic Coast: A Natural History 2011
David L. Kendall Glacier and Granite 1987
The Maine Geological Survey makes its surficial geology map available on line, in a printable 11x17 inch format. It has lots of good info on the results of the last glacial advance and retreat, and it’s free!
http://www.maine.gov/doc/nrimc/mgs/pubs/online/surficial/surficial11x17.pdf
Super nerds unite: check out the Maine Ice Age Trail, and you too can tour Hancock and Washington counties looking at gravel pits (I’ve done it, its awesome). http://iceagetrail.umaine.edu/ also includes an excellent overview of the last ice age in Maine http://iceagetrail.umaine.edu/content/iceageinmaine/iceageinmaine.php
Monday, May 20, 2013
The History of Maine Part 9: The Glacial Landscape
Note: This program first aired May 11, 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 talking about the patterns of glaciation in this past ice age.
As I said last week, each time an ice sheet advances, it essentially wipes out the evidence left by the ice sheet before it, so while there were several cycles of advance and retreat here in Maine, we really only see evidence from the last one.
The ice sheet originated in northern Canada, and spread under its own weight as far south as Long Island New York. It reached its maximum extent some time between 24,000, and 28,000 years ago, mere nanoseconds on the geologic timescale. As a glacier moves over the landscape, it scours the earth, scraping away all the soil and loose debris down to the bed rock. Much of that material gets incorporated into the base of the glacier, frozen into the ice, and acts as giant grit sand paper, further scouring and smoothing the bedrock below. So the first effect of the glacier on Maine’s landscape is one of smoothing, rounding and eroding. The repeated scourings that resulted from the cycles of advance and retreat have given us the rolling landscape we see here today.
By picking up all that surficial material, the glacier is also a very effective earth mover. Rocks originating in bedrock in one part of the state, can be found on the tops of mountains on the other side of the state, confusing many a geologist in the days before the ice age was understood. We can think of the second effect of the glacier as being that of a redistributor of the surface sediments and materials of a Maine.
When the glacier melted, it dropped all of that material in place, so most of Maine is covered with a layer of what is called glacial till, essentially gravel, sand and rocks, broken up to varying degrees and transported in the glacial ice. A glacier is in retreat when the leading edge is melting faster than snow is accumulating at the center. The leading edge melts back and leaves all that till behind. A glacier advances when the snow accumulation rate is higher than the melting rate at the leading edge. Sometimes however, the rate of melting equals the rate of snow accumulation, and the glacier appears to stand still. It isn’t really stationary, as it is still advancing, but the leading edge is melting at the same rate, so the edge of the glacier is stationary relative to the land around it. When this happens the glacier is still melting and dumping till, but it isn’t moving back when it does this, meaning, a big ridge of till piles up at the foot of the glacier. That pile of till is called a moraine, and they are very common on the Maine landscape. My house is built into the end of one. Moraines tend to be hills or ridges full of unsorted till, meaning you find all sizes of materials in them, in no logical pattern. Giant boulders coexist with fine sand or gravel. They were simply dropped where the ice melted, with virtually no sorting of any kind.
Another thing that happens when a glacier melts is the formation of rivers of melt water within and underneath the ice. All that water has to go some were, and channels form in cracks in the ice, that follow gravity and eventually make it to the ground, melting their way out to the snout of the glacier. As the ice melts, it releases its sediment burden, but in this case, the sediment is released into moving water. The energy of the moving water provides a mechanism to sort the sediment; it takes more energy to move a large boulder than it does to move a small grain of sand. Deposits from this melt water are called eskers, and they are characterized by well sorted sediment, making them a favorite for gravel pit operators. They also tend to be quite prominent and run for long distances on top of the surrounding landscape. Many roads in Maine run along the tops of eskers as a result.
We’ll finish today with everyone’s favorite depositional feature of our glacial landscape, glacial erratics. These are large boulders dropped by the glacier as it melted, that stand out prominently on the landscape, instead of being buried in glacial till. In some cases they were deposited as part of glacial till and either by the luck of the draw or erosion of the surrounding sediment, ended up on the surface. In other cases though they were deposited by icebergs. Yes, at many points in the retreat of the last glacier in Maine, the sea came right up to the melting edge of the glacier (much like some of the glaciers in western Greenland today). The melting edge of the glacier could actually float on the sea water, and chunks of it would break off. These chunks or ice bergs still held the rocks, boulders and gravel that makes up glacial till, and as they melted the rocks rained down onto the bottom of the sea. Large boulders deposited this way are called drop stones.
Those are some of the depositional features we see around us here in Maine that resulted from the retreat of the last glacier not so very long ago. We’ll leave off there today, but join us in the coming weeks as we finish up the glacier chapter of the story of Maine’s landscape history.
References
D. W. Caldwell, Roadside Geology of Maine
David L. Kendall Glaciers and Granite: A guide to Maine’s landscape and geology, 1987 North Country Press, Unity Maine
http://nsidc.org/cryosphere/glaciers/life-glacier.html
The National Snow and Ice Data Center (yes there is such a thing!) All About Glaciers!
The Maine Geological Survey makes its surficial geology map available on line, in a printable 11x17 inch format. It has lots of good info on the results of the last glacial advance and retreat, and it’s free!
http://www.maine.gov/doc/nrimc/mgs/pubs/online/surficial/surficial11x17.pdf
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 talking about the patterns of glaciation in this past ice age.
As I said last week, each time an ice sheet advances, it essentially wipes out the evidence left by the ice sheet before it, so while there were several cycles of advance and retreat here in Maine, we really only see evidence from the last one.
The ice sheet originated in northern Canada, and spread under its own weight as far south as Long Island New York. It reached its maximum extent some time between 24,000, and 28,000 years ago, mere nanoseconds on the geologic timescale. As a glacier moves over the landscape, it scours the earth, scraping away all the soil and loose debris down to the bed rock. Much of that material gets incorporated into the base of the glacier, frozen into the ice, and acts as giant grit sand paper, further scouring and smoothing the bedrock below. So the first effect of the glacier on Maine’s landscape is one of smoothing, rounding and eroding. The repeated scourings that resulted from the cycles of advance and retreat have given us the rolling landscape we see here today.
By picking up all that surficial material, the glacier is also a very effective earth mover. Rocks originating in bedrock in one part of the state, can be found on the tops of mountains on the other side of the state, confusing many a geologist in the days before the ice age was understood. We can think of the second effect of the glacier as being that of a redistributor of the surface sediments and materials of a Maine.
When the glacier melted, it dropped all of that material in place, so most of Maine is covered with a layer of what is called glacial till, essentially gravel, sand and rocks, broken up to varying degrees and transported in the glacial ice. A glacier is in retreat when the leading edge is melting faster than snow is accumulating at the center. The leading edge melts back and leaves all that till behind. A glacier advances when the snow accumulation rate is higher than the melting rate at the leading edge. Sometimes however, the rate of melting equals the rate of snow accumulation, and the glacier appears to stand still. It isn’t really stationary, as it is still advancing, but the leading edge is melting at the same rate, so the edge of the glacier is stationary relative to the land around it. When this happens the glacier is still melting and dumping till, but it isn’t moving back when it does this, meaning, a big ridge of till piles up at the foot of the glacier. That pile of till is called a moraine, and they are very common on the Maine landscape. My house is built into the end of one. Moraines tend to be hills or ridges full of unsorted till, meaning you find all sizes of materials in them, in no logical pattern. Giant boulders coexist with fine sand or gravel. They were simply dropped where the ice melted, with virtually no sorting of any kind.
Another thing that happens when a glacier melts is the formation of rivers of melt water within and underneath the ice. All that water has to go some were, and channels form in cracks in the ice, that follow gravity and eventually make it to the ground, melting their way out to the snout of the glacier. As the ice melts, it releases its sediment burden, but in this case, the sediment is released into moving water. The energy of the moving water provides a mechanism to sort the sediment; it takes more energy to move a large boulder than it does to move a small grain of sand. Deposits from this melt water are called eskers, and they are characterized by well sorted sediment, making them a favorite for gravel pit operators. They also tend to be quite prominent and run for long distances on top of the surrounding landscape. Many roads in Maine run along the tops of eskers as a result.
We’ll finish today with everyone’s favorite depositional feature of our glacial landscape, glacial erratics. These are large boulders dropped by the glacier as it melted, that stand out prominently on the landscape, instead of being buried in glacial till. In some cases they were deposited as part of glacial till and either by the luck of the draw or erosion of the surrounding sediment, ended up on the surface. In other cases though they were deposited by icebergs. Yes, at many points in the retreat of the last glacier in Maine, the sea came right up to the melting edge of the glacier (much like some of the glaciers in western Greenland today). The melting edge of the glacier could actually float on the sea water, and chunks of it would break off. These chunks or ice bergs still held the rocks, boulders and gravel that makes up glacial till, and as they melted the rocks rained down onto the bottom of the sea. Large boulders deposited this way are called drop stones.
Those are some of the depositional features we see around us here in Maine that resulted from the retreat of the last glacier not so very long ago. We’ll leave off there today, but join us in the coming weeks as we finish up the glacier chapter of the story of Maine’s landscape history.
References
D. W. Caldwell, Roadside Geology of Maine
David L. Kendall Glaciers and Granite: A guide to Maine’s landscape and geology, 1987 North Country Press, Unity Maine
http://nsidc.org/cryosphere/glaciers/life-glacier.html
The National Snow and Ice Data Center (yes there is such a thing!) All About Glaciers!
The Maine Geological Survey makes its surficial geology map available on line, in a printable 11x17 inch format. It has lots of good info on the results of the last glacial advance and retreat, and it’s free!
http://www.maine.gov/doc/nrimc/mgs/pubs/online/surficial/surficial11x17.pdf
The History of Maine Part 8: Ice Age Patterns
Note: This program first aired May 4, 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 talking about the basic mechanics of continental glaciers, from their formation to their plastic-y deformation and movement.
The most recent ice age on Earth began about two and a half million years ago, and marked the beginning of what geologists refer to as the Quaternary Period. This ice age was the culmination of a gradual cooling trend in Earth’s overall climate that began about 75 million years ago, while dinosaurs still roamed the Earth. On the geologic time scale, two and a half million years is chump change, and when compared to the time required for opening and closing of an ocean or the subduction of a plate, it is hard to believe anything significant could happen to a landscape in such a short time. But believe it. The effects of the ice age absolutely define the hardscrabble nature of Maine’s land forms and biotic communities today.
The ice age that began two and a half million years ago* is actually a series of repeating expansions and retreats of continental glaciers, which originate at high latitudes, and spread into temperate or mid latitudes at their furthest reach. The pattern has been generalized as 100,000 year cycles, about 60-90 thousand years of glaciation, followed by a warmer period lasting 10 to as much as 40 thousand years, but there is certainly variability. These warmer periods are called interglacials, and we are in one right now—if we weren’t, Maine winters and summers would be a whole lot colder than we currently experience.
It is difficult to say with certainty just how many times the continental glacier that originated in northern Canada advanced over the landscape of Maine, as each glacial advance essentially obliterates all evidence left by the glacial advance before it. Billions and billions of pounds of one to two mile thick ice quite literally wipes the slate clean every where it goes. But we do have a very clear picture of the global climate during this time, which gives us a good sense of cooler periods and warmer periods, which are relatively safe to correlate with periods of glacial advance and retreat in the northern hemisphere. The climate record is recorded in the ice sheets that persist today (in Antarctica, in Alaska, in Greenland). Scientists drill into these ice sheets and retract a core (essentially a long skinny tube) of ice. Remembering that glaciers are formed from repeated snow fall, researchers can actually discern the layers of snow, compressed but still distinct, and like scientists looking at tree rings, actually reconstruct the climate history with amazing resolution. Tiny bubbles of gas from the fossil atmosphere and dust, ash and other atmospheric particles are clues that aid this research.
While all this glacial activity was going on, and the Earth was over all a bit cooler and probably a bit drier as well, something else was happening, something we are pretty interested in. Importantly for us, this past ice age coincides with the period of hominid evolution, us. While it is impossible to say that humans evolved because of the ice age, it is true that we evolved in a relatively uncommon climatic regime. In the big picture, Earth has been much much warmer than it is now, humans evolved during a cool spell. While it is hard to predict with any certainty just how hot it will get as a result of human influenced climate change, the possibility that keeps climate scientists up at night is that it will get warmer than humans, ANY humans have ever experienced. That is the kind of climate shift that marks the end of the evolutionary line for many a species. We see it over and over again in the fossil record. That is why many people define climate change as an existential threat, it is estimated that 99% of every species that has lived on Earth is extinct, primarily due to the fact that they were not able to evolve fast enough to adapt to rapidly changing climate regimes. Ice ages come and ice ages go, changing the shape of the land along the way, but probably more importantly, ice ages are a symptom of instability in the global thermostat, with significant repercussions for everything that lives on Earth.
We digressed a bit today, but join us next week as we get back on track and look at the direct impact of the glaciers on the landscape of Maine.
References:
Caldwell, D. W. Roadside geology of Maine
http://nsidc.org/cryosphere/glaciers/life-glacier.html
The National Snow and Ice Data Center (yes there is such a thing!) All About Glaciers!
Super nerds unite: check out the Maine Ice Age Trail, and you too can tour Hancock and Washington counties looking at gravel pits (I’ve done it, its awesome). http://iceagetrail.umaine.edu/ also includes an excellent overview of the last ice age in Maine http://iceagetrail.umaine.edu/content/iceageinmaine/iceageinmaine.php
Nice bigger picture material from PBS (written quite a while ago by a UMaine researcher):
http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html
Some scholarly business, though there has been a flurry of research in the past two decades on ice sheets, so this is likely a bit dated: Richmond, G.M. and D.S. Fullerton, 1986, Summation of Quaternary glaciations in the United States of America. Quaternary Science Reviews. vol. 5, pp. 183-196
On Extinction—From the Bristol University late Triassic Website: http://palaeo.gly.bris.ac.uk/palaeofiles/triassic/extinction.htm
Explore UMaine’s Climate Change Institute http://climatechange.umaine.edu/ especially this link to the basics of ice core research:
http://climatechange.umaine.edu/icecores/IceCore/Ice_Core_101.html
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 talking about the basic mechanics of continental glaciers, from their formation to their plastic-y deformation and movement.
The most recent ice age on Earth began about two and a half million years ago, and marked the beginning of what geologists refer to as the Quaternary Period. This ice age was the culmination of a gradual cooling trend in Earth’s overall climate that began about 75 million years ago, while dinosaurs still roamed the Earth. On the geologic time scale, two and a half million years is chump change, and when compared to the time required for opening and closing of an ocean or the subduction of a plate, it is hard to believe anything significant could happen to a landscape in such a short time. But believe it. The effects of the ice age absolutely define the hardscrabble nature of Maine’s land forms and biotic communities today.
The ice age that began two and a half million years ago* is actually a series of repeating expansions and retreats of continental glaciers, which originate at high latitudes, and spread into temperate or mid latitudes at their furthest reach. The pattern has been generalized as 100,000 year cycles, about 60-90 thousand years of glaciation, followed by a warmer period lasting 10 to as much as 40 thousand years, but there is certainly variability. These warmer periods are called interglacials, and we are in one right now—if we weren’t, Maine winters and summers would be a whole lot colder than we currently experience.
It is difficult to say with certainty just how many times the continental glacier that originated in northern Canada advanced over the landscape of Maine, as each glacial advance essentially obliterates all evidence left by the glacial advance before it. Billions and billions of pounds of one to two mile thick ice quite literally wipes the slate clean every where it goes. But we do have a very clear picture of the global climate during this time, which gives us a good sense of cooler periods and warmer periods, which are relatively safe to correlate with periods of glacial advance and retreat in the northern hemisphere. The climate record is recorded in the ice sheets that persist today (in Antarctica, in Alaska, in Greenland). Scientists drill into these ice sheets and retract a core (essentially a long skinny tube) of ice. Remembering that glaciers are formed from repeated snow fall, researchers can actually discern the layers of snow, compressed but still distinct, and like scientists looking at tree rings, actually reconstruct the climate history with amazing resolution. Tiny bubbles of gas from the fossil atmosphere and dust, ash and other atmospheric particles are clues that aid this research.
While all this glacial activity was going on, and the Earth was over all a bit cooler and probably a bit drier as well, something else was happening, something we are pretty interested in. Importantly for us, this past ice age coincides with the period of hominid evolution, us. While it is impossible to say that humans evolved because of the ice age, it is true that we evolved in a relatively uncommon climatic regime. In the big picture, Earth has been much much warmer than it is now, humans evolved during a cool spell. While it is hard to predict with any certainty just how hot it will get as a result of human influenced climate change, the possibility that keeps climate scientists up at night is that it will get warmer than humans, ANY humans have ever experienced. That is the kind of climate shift that marks the end of the evolutionary line for many a species. We see it over and over again in the fossil record. That is why many people define climate change as an existential threat, it is estimated that 99% of every species that has lived on Earth is extinct, primarily due to the fact that they were not able to evolve fast enough to adapt to rapidly changing climate regimes. Ice ages come and ice ages go, changing the shape of the land along the way, but probably more importantly, ice ages are a symptom of instability in the global thermostat, with significant repercussions for everything that lives on Earth.
We digressed a bit today, but join us next week as we get back on track and look at the direct impact of the glaciers on the landscape of Maine.
References:
Caldwell, D. W. Roadside geology of Maine
http://nsidc.org/cryosphere/glaciers/life-glacier.html
The National Snow and Ice Data Center (yes there is such a thing!) All About Glaciers!
Super nerds unite: check out the Maine Ice Age Trail, and you too can tour Hancock and Washington counties looking at gravel pits (I’ve done it, its awesome). http://iceagetrail.umaine.edu/ also includes an excellent overview of the last ice age in Maine http://iceagetrail.umaine.edu/content/iceageinmaine/iceageinmaine.php
Nice bigger picture material from PBS (written quite a while ago by a UMaine researcher):
http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html
Some scholarly business, though there has been a flurry of research in the past two decades on ice sheets, so this is likely a bit dated: Richmond, G.M. and D.S. Fullerton, 1986, Summation of Quaternary glaciations in the United States of America. Quaternary Science Reviews. vol. 5, pp. 183-196
On Extinction—From the Bristol University late Triassic Website: http://palaeo.gly.bris.ac.uk/palaeofiles/triassic/extinction.htm
Explore UMaine’s Climate Change Institute http://climatechange.umaine.edu/ especially this link to the basics of ice core research:
http://climatechange.umaine.edu/icecores/IceCore/Ice_Core_101.html
Subscribe to:
Posts (Atom)