For tens of thousands of years, Maine was covered by the Laurentide Ice Sheet - a sheet of ice that was over a mile thick. The weight of the ice was so great, it pressed the earth’s crust into the mantle, lowering the level of the land. By 14,000 years ago, the ice in Maine had retreated to the northern part of the state, leaving moraines, eskers, glacial outwash plains, till, and erratics on land that was meters lower than it is today. With the land depressed and sea levels rising due to the meltwater coming off of the Laurentide, what is today called Maine flooded.
From Mount Desert Island to Bangor, land less than 420 feet in elevation in central Maine was covered by the sea. Marine and glacial sediments mixed, creating the Presumpscot Formation, the layer of soft gray clay that lies beneath the topsoil, lining much of coastal and central Maine today and is used to make pottery. We know that the sea came so far inland because this layer of clay (found even at Hirundo!) contains marine fossils, such as mollusk and clam shells and occasionally seal and whale bones. But, by 12,200 years before present, the land had rebounded and the sea was back in the Gulf of Maine.
Until approximately 10,000 years ago, the plants and animals of the region looked fairly different from the way they do today. The Wabanaki people were here as soon as the ice retreated, along with wooly mammoths, giant beavers, and caribou that we see in the fossil record. The giant beavers alone were over eight feet tall and weighed over two hundred pounds. The Wabanaki people have stories of these creatures that are still shared today. The land would have been fairly wet at this time, with the Presumpscot clay creating a bathtub-like lining, which, when combined with ice chunks and depressions left by the ice sheet, created many of the lakes we know and love today. The land was still fairly tundra-like, covered in grasses, sedges, herbs, shrubby birch, alder, spruce, fir, Jack pine, oak, and hornbeams. It has since changed in the last 10,000 years, going through many changes in climate, plants, animals, and human activity, to look the way it does today.
Left: Giant Beaver compared to Human. Right: Mammoth Tooth
How do we reconstruct past environments?
Postglacial environments can be difficult to reconstruct due to the acidic nature of Maine’s soils. The acid in the soils breaks down bones left by animals and items that would typically be found in the archaeological record. There are still records that exist in our soils, but sometimes we have to use different tools to look at the past, such as lake sediments.
Lake sediments act as timelines preserved at the bottom of bodies of water. They are environments that typically remain undisturbed for millennia and do not contain oxygen, making them great preservers of the past. We can extract lake sediments and analyze them for different proxies, which are indirect lines of evidence we use to reconstruct the past.
Hirundo Student Trustee Madi Landrum extracting Pollen Core
Some tools to reconstruct the past:
Pollen is one of the toughest materials that exists and can remain intact for millions of years. However, once exposed to oxygen, it begins to break down. Each plant produces a differently sized and shaped pollen grain with different textures, or sculpturing, on the surface. We can look at pollen from slices of sediment dating pack to the appearance of the first plants in Maine after the ice left to see what plants arrived first and how the composition of the forests changed over the last 12,000 years.
Charcoal: We can also look at fragments of charcoal in our samples and use them to reconstruct fire patterns across space and time. Different plants and their composite parts burn differently, so we can use the size, shape, and transparency of the charcoal types to broadly see what material was burning and when on the landscape.
Lipid biomarkers: lipid biomarkers are a new tool being used to see human and animal presence on the landscape in places that the archaeological record may no longer exist. It uses cholesterol chains produced by our gut microbiomes that were washed into lakes to show human and animal presence on a landscape. People, omnivores, and herbivores all produce different types of cholesterol chains, which makes it possible for us to see who and what was on the landscape.
When we combine these proxies with archaeological and climate records, we begin to see the complex relationships that existed between people, plants, fire, and climate on a landscape. We are in the process of working up these records at Hirundo and hope to be able to share the dynamic story of this wildlife refuge over the millennia with you soon!
References:
Beck, J.C., 1972, The giant beaver: a prehistoric memory? Ethnohistory, v. 19, no. 2, p. 109-122.
Borns, H. W., Jr., Doner, L. A., Dorion, C. C., Jacobson, G. L., Jr., Kaplan, M. R., Kreutz, K. J., Lowell, T. V., Thompson, W. B., and Weddle, T. K., 2004, The deglaciation of Maine, U.S.A., in Ehlers, J., and Gibbard, P. L. (editors), Quaternary glaciations - extent and chronology, Part II: North America: Elsevier, Amsterdam, p. 89-109.
Davis, R.B., Bradstreet, T.E., Stuckenrath, R., Jr., and Borns, H.W., 1975, Vegetation and associated environments during the past 14,000 years near Moulton Pond, Maine, Quaternary Research, v. 5, p. 435-465.
Davis, R. B., and Jacobson, G. L., Jr., 1985, Late-glacial and early Holocene landscapes in northern New England and adjacent areas of Canada: Quaternary Research, v. 23, p. 341-368.
Dorion, C. C., Balco, G. A., Kaplan, M. R., Kreutz, K. J., Wright, J. D., and Borns, H. W., Jr., 2001, Stratigraphy, paleoceanography, chronology, and environment during deglaciation of eastern Maine, in Weddle, T. K., and Retelle, M. J. (editors), Deglacial history and relative sea-level changes, northern New England and adjacent Canada: Geological Society of America, Special Paper 351, p. 215-242.
Hoyle, B.G., Fisher, D.C., Churchill-Dickson, L.L., Dorion, C.C., Weddle, T.K., 2004, Late Pleistocene mammoth remains from Coastal Maine, USA, Quaternary Research, V. 61, p. 277-288.
Speck, F.G., 1935, Penobscot tales and religious beliefs, The Journal of American Folklore, v. 48, issue 148, p. 1-107.
Thompson, W.B., 1987, The Presumpscot Formation in southwestern Maine, Maine Geological Survey.
