Fossil Landscape Revealed: Reading the Rocks in New England Summits

It’s remarkable to think that we are discovering ice on a dwarf planet 4.67 billion miles (7.5 billion kilometers) away from Earth, at a time when we are still unraveling clues to the ice that once shaped this planet.

Two New England geologists have spent years studying the rocks and traces left by ancient glaciers in the White Mountains, the northern stretch of the Appalachian Mountains in New Hampshire and Maine. This past October, they co-authored a paper in Geology with 3 other scientists.  And in it, they revealed that the highest summits in New England were covered by solid ice during the Last Glacial Maximum.

 

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View from the summit of Mount Moriah in New Hampshire looking at the White Mountains’ Presidential Range; image by Cappi Thompson at Getty Images.

 

But what does this mean? And why should we care?

“This question about whether or not the New England summits were covered by an ice sheet is long standing, going back over 100 years,” explained Dr. P. Thom Davis by phone.  “And one reason this question is important is because continental ice sheets take a long time to build up, and as they build up, they reduce global sea level.   So ice sheet thickness has implications far beyond just New England.”

Dr. Thom Davis of Bentley University and Dr. Paul Bierman of the University of Vermont actually wrote and presented the paper at the annual Geological Society of America conference in 1999, but they didn’t publish it until 2015.

“We sent a draft around informally to some colleagues,” said Dr. Davis, “and they sort of were giving us a hard time, wanting us to go back and rethink a lot of the implications. And then one thing led to another, and we just kept rethinking and rethinking for the next 15 years.”

“It was a much more radical proposition in 1999 than it is today,” explained Dr. Bierman. “Since then a whole lot of work has come out of the Arctic. So when we finally submitted this now, I guess it was a surprise, but it wasn’t unexpected.”

That ‘radical proposition’ involved whether or not ice covered the mountains, whether it was a certain type of ice, and therefore whether it did or did not preserve “fossil” or “relic” landscapes.   These ideas have been pondered (or dismissed) by various geologists since the mid 1800s.

While the term “fossil landscape” might inspire images of preserved prehistoric environments suffused with traces of ancient life, this is not at all what it means.  Rather, it refers to the geology left behind by cold-based ice–ice frozen all of the way to the ground–that both shielded rocks from the effects of cosmic rays and slowed erosion.

Think of how much impact an enormous sheet of ice can have on an environment.  When ice is not completely frozen to the ground (warm-based ice), water runs through it, pulling dirt, rocks–and the glacier itself!–along with it.  The ground erodes; the debris is carried elsewhere. Remnants can be seen in boulders scattered throughout New England.

Notice the shape of the valley in Crawford Notch, NH.  This valley is a result of glacier ice moving through the environment, albeit at a remarkably slow speed. Image by Mark Zelasko at Getty Images.

Boulder in Salisbury, NH

 

Detail of boulder in Salisbury, NH

Images of a boulder (perhaps a glacial erratic: a rock carried by a glacier and deposited in another location in geologic terms) in Salisbury, NH; photos taken by the author

 

“The word ‘fossil landscape’ sort of worried me from the get-go because of how it might be misconstrued to having more of a biological context, like mammoth bones,” stated Dr. Davis, in reference to the press release describing their work. “We’re looking at the age of exposure, the length of time those surfaces have been exposed to the cosmic ray bombardment.”

Drs Davis and Bierman collected samples near to or on the summits of Mt. Katahdin in Maine and Mt. Washington and Little Haystack Mountain in NH during the 1990s.  Their ‘radical’ suspicion–that these summits were indeed covered by solid ice–could only able be proven recently with advanced technology.

Before that, they–like their peers in the last two centuries–relied on visible clues: the type of rock on summits and in valleys, striations (or grooves) in the rocks that may have been made by  ice, the type of sediment in the valleys and whether this indicated the type of glacier that might have helped create them.  And one of the biggest clues?

Erratics.

“That is,” Dr. Davis explained, “stones that have been transported from another location.”

“Two centuries ago, scientists might have argued [that erratics] were deposited in these high locations by great floods,” he continued. “But that pretty much ended with Agassiz’s glacial theory in the middle of the 1800s.”

He is referring to Louis Agassiz, an eminent Swiss biologist and geologist who taught at Harvard, and perhaps the first to support the idea that these summits were covered by an ice sheet.  It is important to note, however, that he believed that ice sheet was a local glacier rather than a vast continental ice sheet.

Prior to this, geologists such as Charles T. Jackson–the first NH State Geologist–or Edward Hitchcock (of trace fossil fame) believed that a flood complete with icebergs was responsible for misplaced boulders. Striations could be explained by the force of rock against rock from powerful currents within that water.

British citizens Mary Horner Lyell and her husband, Charles–another well-known geologist from the 1800s–explored these mountains in 1845, including a trip up Mt. Washington on horseback. Lyell attributed erratics to melting icebergs.

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Frozen tower and communication equipment at the summit of Mt. Washington; image by Onfokus at Getty Images.  Charles Hitchcock — son of Edward and Orra Hitchcock — helped create this year-round weather station.  He was a NH State Geologist and a Dartmouth professor. 

NH geology took a step forward with James W. Goldthwait and then later his son, Richard, in the 1900s.  They proposed that New England summits were covered by solid ice–not warm-based ice–and by a continental–not a local–ice sheet.

“[James W. and Richard P. Goldthwait] recognized this importance long ago, from the turn of the last century,” said Dr. Davis. ‘They both recognized very fresh looking erratics. The only way erratics can arrive on these summits is by continental ice sheets.”

“They made a really good case that the last ice sheet that dropped these erratics on the summits happened during our last glaciation about 20,000 years ago. [I]f the summits had been nunataks during the last major glaciation about 20,000 years ago, then the erratics should have been more weathered, the soils should have been more developed on the summit areas, and the bedrock should have been more weathered, as well.”

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Baxter Peak of Mount Katahdin in Baxter State Park, Maine. View from Knife Edge Trail; image by Posnov at Getty Images.

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Mount Katahdin is the highest mountain in Maine at 5,268 feet (1,606 m). Katahdin is the centerpiece of Baxter State Park: a steep, tall mountain formed from underground magma; image by Simon Massicotte at Getty Images.

The debate about the type of ancient ice in the White Mountains was dropped for a few decades, slowly regaining interest in the 1970s.  But it wasn’t until the recent paper by Drs. Bierman and Davis that proof lent itself to solving the issue.

“[Our method was to] count the abundance of very, very rare isotopes,” Dr. Bierman explained, “And, by that we mean isotopes of the element beryllium and the element aluminum.”

“The beryllium isotope with a total mass of 9 is the normal stuff that you find in nature. The beryllium isotope with a total mass of 10 per atom is extremely rare. And in order to measure these isotopes, we needed the technical ability to do that, and that didn’t come about until the late 1970s with a device called the accelerator mass spectrometer. These are very large, very expensive, difficult to maintain, and rare beasts. Over the past 30 years, they’ve been used increasingly by geologists to make the kinds of measurements that we did.”

“We also used cosmogenic carbon-14,” he continued, “which is an isotope with a much shorter half-life, about 5,730 years. And what that means is that when a rock is exposed to cosmic rays at the surface and then buried, that carbon 14 disappears much more rapidly than beryllium 10 and aluminum 26 isotopes.

“[Data from the accelerator mass spectrometer] tells us the [exposure] age because we can count the number of carbon-14 atoms, just like we can count the beryllium-10 atoms. We know that these are produced at a certain rate every year. It’s a very low rate.

“For beryllium-10, it’s just a few atoms per year per gram of material that we’re measuring. It’s a little bit more for carbon-14.  And since we know how quickly they’re made and we can count how many atoms there are, we can calculate an age–or a residence time–near the surface.”

“A lot of these ages from our exposure dating,” added Dr. Davis, “were coming out much older than we expected, much older than the last glaciation from the summits of both Katahdin and Mt. Washington.”

 

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A view of Mt Washington and Mt Madison along some farmland in Shelburne, New Hampshire during winter; image by Cappi Thompson at Getty Images.

“I think the Goldthwaits were primarily looking at these kinds of qualitative data, like how fresh the erratics in the bedrock were,” Dr. Davis offered. “And based on that, they probably weren’t exposed very long.  But as it turns out, weathering varies dramatically to different latitudes, so is not a very quantitative method. That’s all we had, though, until these cosmogenic radionuclides became available for measuring.”

“The main point of our geology paper is that, apparently, even at temperate latitudes, the higher elevations may have been overrun by ice sheets that were frozen to the bed, leaving what we call ‘relic landscapes,'” he concluded.

“From a geologic point of view,” Dr. Bierman continued, “it points to the complexity of the evolution of the New England landscape. It’s another piece of the puzzle in how this landscape evolved over time.”

 

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Sunrise clouds above the White Mountains’ Presidential Range in Jefferson, New Hampshire; image by Cappi Thompson at Getty Images.

Old_Man_of_the_Mountain_4-26-03

 

Old Man of the Mountain–an iconic NH rock formation, one that seems appropriate to share in a blog post on geology–on April 26, 2003, seven days before the rocks of its face collapsed. A late spring snow fell the night before. Image by Jeffrey Joseph, public domain, Wikipedia.

Dr. P. Thom Davis and Dr. Paul Bierman not only introduced me to a new science, they also piqued my interest in it. Basic geologic vocabulary was foreign to me. I delighted in discovering the meaning behind new words (nunataks, moraines, varve records, basal thermal regime!) in order to better understand their work. Thanks to their time and their research, I now look at the world around me with much more discerning eyes, especially at the many boulders erratics that scatter the landscape.  Fossils in New England may be scarce, but rock formations are not.  I extend a sincere and resounding THANK YOU to both, for their help, their graciousness and the fun three-way conversation we had discussing their paper!

Thank you to Kea Giles at the Geological Society of America for sending me a copy of the paper!

I highly recommend the book “The Geology of New Hampshire’s White Mountains” shown below, co-authored by Dr. P. Thom Davis. It is a fascinating account of NH geology and a great introduction to geology itself.

Woodrow Thompson, another co-author of that book, wrote an engaging account of the history of NH geology (paper is listed below). It was a great help to me in writing this piece, and I encourage anyone interested to read it

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References:

  1. Fossil Landscapes in New England, GSA press release, October 26, 2015
  2. Cold-based Laurentide ice covered New England’s highest summits during the Last Glacial Maximum, Paul R. Bierman, P. Thompson Davis, Lee B. Corbett, Nathaniel A. Lifton, Robert C. Finkel, Geology, October 2015
  3. History of Research on Glaciation in the White Mountains, New Hampshire (U.S.A.), Woodrow B. Thompson, Géographie physique et Quaternaire, Volume 53, 1999
  4. The Geology of New Hampshire’s White Mountains, J. Dykstra Eusden, Woodrow B. Thompson, Brian K. Fowler, P. Thom Davis, Wallace A. Bothner, Richard A. Boisvert, John W. Creasy; Durand Press, 2013

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Dr. Brooke Crowley – Secrets Revealed from Mammoths & Mastodons in the Cincinnati Region

It may seem unlikely to uncover details about what an animal ate thousands of years after its extinction, absent of so much of the flora and fauna that co-existed with that animal.

It might seem even more improbable to illicit that information from fossilized teeth alone.

And yet, this is exactly what Dr. Brooke Crowley and Eric Baumann of the University of Cincinnati have done.

Brooke and Eric Baumann on Kardung La

[image of Eric Baumann and Dr. Brooke Crowley on Khardung La, India; courtesy of Dr. Crowley)

They sampled molars from eight different mammoths and four mastodons, each with a known provenance in the Cincinnati region. Analyzing stable isotopes within each tooth provided information not only about each animal’s diet, but also its habitat.

“Isotopes in our tissues,” Dr. Crowley, Assistant Professor of Quaternary Paleoecology, explained in a phone interview, “are environmental integrators.”

“What we like to say is that isotope values in an animal’s tissues can tell you something about its life. That could be the diet, it could be the environment the animal inhabits, or, in the case of strontium, it could be the actual locality where it lives.”

Over the past 30 years, studying stable isotopes has become an increasingly popular method of understanding both paleontological and archaeological finds in more depth.

These chemical signatures reveal details incorporated within the body over its lifetime and remain in its bones past its death. In other words, what one eats and drinks leave traces of elements that point back to that very same diet and to the region from which one drank water. That organic material has footprints, and scientists—using mass spectrometers and other types of analysis—can read and interpret them.

Remarkably, these chemical footprints remain, even after thousands upon thousands of years. And teeth, with their sturdy crystalline structure, seem to offer reliable stable isotope data.

Dr. Crowley and recent graduate Eric Baumann described their research in a paper to be published in Boreas. Carbon isotopes revealed broad information about what these twelve proboscideans ate; strontium and oxygen isotopes uncovered the region and climate in which these animals lived.

They began their research expecting to uncover that the two species were nomadic, that their teeth were discovered in areas geographically distant from their place of origin. They also expected that mammoths and mastodons ate different types of vegetation.

While their research confirmed the different diet, it provided surprising results for habitat: with the exception of one mastodon, all of these animals actually lived and remained within the Cincinnati region.

In response to why they originally thought these animals might be nomadic, Dr. Crowley pointed to the behavior of existing species.

“Most large animals aren’t sedentary.”

“In general,” she explained, “big creatures move a fair amount; they have large stomachs and they eat a lot of food. And there may be different reasons for moving. It could be a dietary need, it could be there’s some particular nutrient in the soil that they want from time-to-time, or there may be a particular region they like for birthing or mating.”

We see this today in humpback, gray and blue whale populations on either side of the North American continent, migrating from warmer regions in the ocean to colder regions thousands of miles north.

“African elephants, in particular, are typically very destructive by nature. They are what we call ‘environmental engineers.’ Their behavior changes the environment around them.”

Perhaps the most notable affect elephants leave in their wake are the trees they knock down. Consider, too, that elephants eat 160 – 300+ pounds of vegetation a day per elephant.

“[T]hey heavily modify an area. Then they move and modify another area. And they typically have pretty large home ranges. Some populations seasonally migrate from one place to another; others are just more continuously on the move.”

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But, she cautions, “we can’t necessarily use that information to interpret the behavior of extinct species. They’re not necessarily that closely related. But it is something we have to go on.”

In their research, the authors include data from water samples taken from rivers and creeks in Ohio and Kentucky.

What, one might wonder, do modern-day water samples have to do with ancient teeth and their composition?

Strontium within water reflects the geology from which it came. This information is stored within teeth, thereby leaving yet more footprints the scientists can interpret.

Of the types of isotopes analyzed, Dr. Crowley explained that “[a] lot more work has been conducted on carbon and oxygen. So we didn’t really need to establish a local baseline for either of those two isotopes. But strontium’s a little less studied, and we didn’t know what sort of regional variability to expect.

“Without any comparative baseline, it’s hard to interpret what strontium in the animals might mean. We could say, ‘well, they’re all really similar’, but if we didn’t really know what to expect for this region, we wouldn’t know if they’re similar to the region or if all of those animals may have come from somewhere else. So we needed to establish a local baseline.”

In other words, they needed to understand the chemical signatures within local water in order to see if they matched the chemical signatures within these teeth.

“[This is] the first step,” she continued, “in what will hopefully be a long-term research direction: thinking about North American fauna and ecological change over time here on our own continent.”

When asked if this meant she would study other extinct animals or continue researching mammoths and mastodons, her response was “potentially both.”

“Currently I’m [working on a] project using strontium isotopes to look in a little more depth at particular individuals.”

Brooke and a bison scapula

[image of Dr. Brooke Crowley with a bison scapula; courtesy of Dr. Crowley]

She referenced a mastodon from Michigan as an example.

“[W]e’ve sampled little increments of his tusk to see how he moved during his lifetime.”

“One drawback of teeth,” she mentioned, “is that they just give you a relatively brief snapshot in time, whereas a tusk gives you a continuous record of an individual’s life.”

But she is equally interested in what she described as “big-scale patterns” of behavior across various species. And in this research, ‘behavior’ refers to details about their diet, and whether specific species roamed or remained in a specific region.

“If there is any living taxa that we could sample,” she added, “it would be interesting to see how they may have changed, even if they didn’t go extinct.”

“There’s interesting work that’s been done,” she said, referring to research of one of her colleagues, “[regarding the origins of] fossil deposits that indicates mastodons may have retreated to a particular part of the United States just before the Terminal Pleistocene.”

The Pleistocene is a period of time on earth that dates from about 2 million years ago through about 11-10, 000 years ago. The ‘Terminal Pleistocene’ refers to an extinction event within this period.

“Prior to the Terminal Pleistocene, they were found all over the United States. At the Terminal Pleistocene, they’re only found in a little tiny patch of the United States. Something affected their distribution. And I call it ‘retreat’ because it’s a much smaller distribution than they had before.

“By analyzing isotopes in bones and teeth, we would potentially be able to build off of these fossil distributions to paint a more interesting ecological picture of the Terminal Pleistocene.”

Painting more interesting ecological pictures is a strong focus of Dr. Crowley’s work. A scientist who has travelled extensively throughout the world, her research has taken her to the Canary Islands, the Dominican Republic, Trinidad and Madagascar. Reading her blog and her website, one recognizes a distinct fondness for the aforementioned African country.

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When asked if Madagascar was where her heart was, she responded, “In many ways, yes. Part of that is that I’ve devoted a lot of time and energy into learning a lot about it. So, now I’m invested.”

“There are certainly conservation issues in our own country,” she continued, “but there are other places–and Madagascar is one of them–where there’s a real need to try to make some changes happen now for future conservation and biodiversity management.”

“Up until recently, the recent past of Madagascar was rather understudied. It turns out that there are a lot of interesting questions that are still unanswered.”

Her website, Agoraphotia.com, describes her specific interests:

I investigate ecological interactions among living and recently extinct animals using stable isotope biogeochemistry. My interests include niche partitioning, conservation biology, and paleoecology. I am particularly interested in the causes and consequences of recent extinctions, and the ecological repercussions of habitat fragmentation and degradation.

She has studied fossilized rodents, lemurs and orangutans; she has researched climate change; she has studied plants and soil.

She lists research projects in which she has been involved:

•Assessing the utility of stable oxygen isotopes in distinguishing dietary niches.

•Distinguishing isotopic niches of fossil rodents in the Dominican Republic.

•Establishing the stable isotope ecology of modern and Prehistoric Trinidad.

•Exploring ecological change following human settlement on the Canary Islands.

•Identifying responses of the animal community to climate change and human impacts in Madagascar.

•Quantifying spatial variability in bioavailable strontium and assessing changes in mobility patterns of extinct and extant North American megafauna.

Prior to the University of Cincinnati, she lectured at the University of Toronto and volunteered at the Royal Ontario Museum in the OWLS (Open the World of Learning to Students) program.

She describes herself as “a relatively new professor in Cincinnati”, one who actively works to try and include students into her research projects. In this, she feels she has been successful, as she has had a number of students involved in her postdoctoral and graduate research and currently has students working with her in the lab.

The study of proboscidean teeth that lead to the paper to be published in Boreas was, she said, “originally designed to be a student project.”

Given her vast and varied experience, one might wonder why the focus was extinct North American fauna.

Explaining that most of her students are either from Ohio or the surrounding region, she said, “It’s a little more relevant for them to think about animals that lived in their backyard than animals that lived on the other side of the planet.”

This, too, is why they used teeth from the Cincinnati Museum of Natural History, rather than the collections of other neighboring state museums.

Brooke in Madagascar2

[image of Dr. Crowley in Madagascar next to a sign that warns visitors that “Lake Ravelobe is forbidden” and that “Crocodiles attack”; courtesy of Dr. Crowley]

“Many of the reasons that I do what I do and that I am where I am is because of other people who have helped me along the way or inspired me. And really one of the biggest reasons that I wanted to go into academia in the first place was because I feel like I have been empowered in many ways to try to make a difference.

“And I feel like that’s something that I can share with others and then try to make a difference by empowering others and helping them find their way and be compassionate as well.

“So that’s sort of my goal.”

She chuckled. “I don’t know how much I have really met that goal, but I do try, and I’m still pretty new to being a professor. So, I’m finding my way. It’s a challenge, but it’s a good learning experience, and I find it to be pretty rewarding.”

Brooke on a promontory in Tenerife

[image of Dr. Crowley on a promontory in Tenerife, Canary Islands; courtesy of Dr. Crowley]

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A Mammuthus primigenius-sized THANK YOU to Dr. Brooke Crowley for her generous time, help and fascinating responses to my questions!  What a great honor to connect with her!

You can read the paper in Boreas, Stable isotopes reveal ecological differences amongst now-extinct proboscideans from the Cincinnati region, USA:  http://onlinelibrary.wiley.com/doi/10.1111/bor.12091/abstract

I had a very difficult time grasping the concept of isotopes. This is due to my struggle with chemistry in general and not a reflection of the gracious people below who took the time to try to help me understand it.  I extend sincere thank you’s to:

  • Dr. Brooke Crowley
  • my dad
  • my sister-in-law who studies science
  • Dr. Suzanne Pilaar Birch (@suzie_birch)
  • Ariel Zych (@Arieloquent) and Science Friday (@scifri)

If you are interested in understanding more, here is further reading:

  1. Dr. Brooke Crowley, Stable Isotope Ecology: http://crowleyteaching.wordpress.com/courses/stable-isotope-ecology/
  2. Stable Isotopes in Zooarchaeology: http://sizwg.wordpress.com/bibliography/
  3. New insight from old bones: stable isotope analysis of fossil mammals, by Mark Clementz: http://www.mammalogy.org/articles/new-insight-old-bones-stable-isotope-analysis-fossil-mammals
  4. Applications of Stable Isotope Analysis, K. Kris Hirst: http://archaeology.about.com/od/stableisotopes/a/si_intro.htm