Do you like physical geography? If so, the clip below may interest you. It presents results from the analysis of the glacial deposits contained in soils. By mapping these deposits and dating the shells found in ancient glacial lakes, geologists and geomorphologists were able to determine when the territory of the Eastern Townships first became habitable. So without further ado, let’s watch the clip and explore the folder. Note: This subject is complicated for those younger than 14.
Enjoy exploring!
On-screen text: Soils
[ Animated character ] Soils
An image of a young sprout in black earth.
[A.C.] Why study soils? What is the link between archaeology and the earliest inhabitants?
On-screen text: The area's suitability for habitation
[ A.C. ] The area’s suitability for habitation
Image of a young sprout in black soil.
[A.C.] The composition of the soil and its layout provide valuable information on the history of landscapes and on the area’s suitability for habitation. The area has not always been habitable!
Scrolling images: Dense coniferous forest; interactive clip of the Earth 480 million to 300 million years ago. The Earth was separated into several continents and formed a single continent known as Pangaea 300 million years ago. The word Appalachians appeared at the meeting point of the continents.
[A.C.] The geological history of the Eastern Townships dates back to the formation of the Appalachian mountain range. The mountain range began to be formed about 450 million years ago, long before the arrival of dinosaurs and humans.
On-screen: An interactive clip of the Earth from 180 million years ago until present day. The continents moved to their current shape. The word Atlantic appeared 160 million years ago.
[ A.C. ] Over the course of some 200 million years, a series of collisions between land masses and ocean floors caused the land to fold and rise, thus creating a mountain range on a supercontinent.
A photograph of a flat, square-shaped stone with the caption Sedimentary shale is displayed on an illustration of a clipboard. Change to a photograph of another stone, triangular in shape, with ridges, and the wording Metamorphic shale. The photo fades out to show images of the Earth in which we see red lava fissures.
[A.C.] Pressure and heat from the collisions altered the rocks on the seabed: Sedimentary shale became metamorphic schist. The rock cracked in several places and formed volcanic extrusions. Then, about 200 years ago, the supercontinent split into several continents.
Scrolling video images: View from the top of a cliff of sandy soil at the water's edge; waves crashing in the middle of the ocean.
[A.C.] These continents gradually moved further apart, making room for the Atlantic Ocean. Thus, the Appalachians ended up on both sides of the ocean. During this entire period and to this day, the two shores of the Atlantic are spreading further apart at a rate of one to five centimetres per year, depending on the latitude.
Scrolling video images: Heavy rainfall over a shaded forest landscape with a sunrise in the background, mountainside covered with shrubs.
[A.C.] This explains the structure of the Appalachians. Rain and wind eroded the rocks, a process which is still underway. But over the past 2 million years, since humans have existed, the history of the Appalachians has been dominated by major glaciations, that of the Northern Hemisphere.
A timeline of glaciations with the markings 0 to 2000 thousand years is shown on an illustration of a clipboard. From top to bottom, the most recent to the oldest: Post-glacial period, Wisconsinan glacial period, Sangamonian interglacial period, Illinoian glacial period, Yarmouthian interglacial period, Kansan glacial period, Aftonian interglacial period, and Nebraskan glacial period.
[A.C.] More than 20 glacial periods of varying significance were spread over the higher latitudes of the Northern Hemisphere. There were 4 main stages, interspersed with interglacial periods similar to the current situation.
Images of glaciers are displayed.
[A.C.] During the glacial periods, the Eastern Townships region was uninhabitable, covered with 2 kilometres of ice.
Scrolling video images: Snowflakes falling in front of a solid background, big shells and stones on sandy soil, mound of shells on sandy soil.
[A.C.] Therefore, the question is to find out when the last ice sheets retreated. A number of geologists and geomorphologists have studied this question. By mapping the debris accumulated at the fronts of glaciers and by dating the shells from glacial lakes, they have succeeded in retracing the retreat of the glaciers.
An interactive map of Canada and the northern United States is displayed on screen, with the title Laurentide Ice Sheet, illustrating glacier melt that began 21 500 years ago and continued until 13 500 years ago. On the map there are red dots at various locations; the more the ice melted, the more red dots there are.
[ A.C. ] Here is a clip of this deglaciation that began 21 500 years ago. The coloured dots represent seashells and organic sediments that have been dated using the carbon-14 dating technique. Their presence indicates that there were no longer glaciers in the area.
An interactive map of Canada and the northern United States 13 500 years ago with red dots is displayed. STOP! is written in red. A magnifying glass appears over the Eastern Townships region. It zooms over the Eastern Townships and the City of Sherbrooke is indicated, with a close-up view of Sherbrooke where an animated clip shows glaciers melting.
[A.C.] Stop! This is an interesting time of the Eastern Townships region. Some 13 500 years ago, the ice was at the American border, very gradually retreating to the north. The accumulation of melted water created glacial lakes. Water levels in these lakes rose as the ice prevented them from flowing into the ocean. Once the ocean became accessible, the lakes emptied and ocean water flooded the area.
An image of an interactive map of the period between 13 000 and 11 000 years ago is displayed. At the beginning, there was the Champlain Sea left of Sherbrooke, then, the lake at Lampsilis located at the same spot.
Scrolling images: Top-down view of a valley of rocks and grass, with snow in the crevices, caribou on the tundra, image of a prehistoric man with a caribou hide with antlers on his head hunting caribou, image of two prehistoric men, hidden behind rocks, who are hunting caribou.
[A.C.] The emptying of the glacial lake at Candona caused the Champlain Sea to flood the St. Lawrence lowlands. Then, slowly but surely, the ground rose, freed from the weight of the ice. The Champlain Sea lost its access to saltwater and gave way to the lake at Lampsilis. All of these bodies of water had been obstacles to access to the land, but their emptying opened up new paths to new habitable sites.
An image of an interactive map from 10 000 years to 5 000 years ago of Canada and the northern United States is displayed. More and more red dots appear. The ice on the continent is melting, covering only the section north of what is currently Quebec and Greenland.
[A.C.] The sediments left behind by the glaciers and increasing temperatures enabled the emergence of vegetation and the formation of layers of soil. About 13 000 years ago, nearly all of the Eastern Townships region was covered with tundra. This attracted caribou. With its milder temperatures and available food, the Eastern Townships region became habitable... at least during the summer periods.
Images of water flowing in a sloped stream, then of running river water with tiny chunks of ice floating in the direction of the current are displayed.
[A.C.] During the subsequent thousands of years, expansion of the habitable area followed the edges of the continental ice and the banks of glacial lakes and inland seas. For archaeologists, the area's suitability for habitation due to the retreat of the ice is significant information. But studying the soils is also interesting for another reason.
On-screen text: Prospecting strategy
[A.C.] Prospecting strategy
A clip of the evolution of a soil, starting from the fragmentation of the bedrock caused by climate conditions is displayed. Growing plants are shown, followed by a photograph of a coniferous forest on a rock wall.
[A.C.] Most of Quebec’s soil was formed from loose sediments that accumulated, before being revealed during the retreat of the glaciers or during postglacial events. In the Appalachians, rock was exposed in several locations, but most often it was covered with glacial or postglacial deposits. There is no hope of finding artifacts on rock.
On screen : An image of bedrock with an upper layer of loose soil and a third upper layer named ground.
On-screen: An image of bedrock with an upper level of sand, and higher up a flat surface with the inscription Terrace. Fade in of an image of the cross-section of soil with several shades of soil: Some artifacts are located deep in the soil and others closer to the surface.
[A.C.] Artifacts with the greatest potential for conservation are those that were left on flat areas, on valley slopes. These terraces were also hospitable environments for the earliest inhabitants. Soil was formed there through changes to loose sediments. When layers were superimposed, the oldest artifacts are those buried the deepest.
Images of a tractor plowing farmland are displayed.
[A.C.] In other cases, artifacts are often moved deeper by the natural burying processes, such as freezing and thawing, or trees falling. A puzzle for archaeologists.
[A.C.] Familiarity with the various models of glacial deposits thus helps archaeologists in their search for artifacts. Another element, equally important, is the phosphate content of the soils.
A schematic image of a phosphate atom with the text Phosphate PO3-4 is displayed. It is followed by a clip of a human body turning into a skeleton, and then an animated image of a laboratory with storage cupboards, test tubes, an oven, measuring instruments, and a microscope.
[A.C.] Phosphates are naturally found in low concentrations in soils. However, they are found concentrated in human bones and excrement. Certain other components, like calcium, nitrogen, and potassium, easily decompose. This does not occur with phosphates. Studying concentrations of phosphates makes it possible to establish the likelihood of human presence when searching for artifacts.
On-screen text: Conclusion
[A.C.] Conclusion
Images scrolling on a clipboard: Image of an expert measuring the depth of the soil at an archaeological site, map of the Eastern Townships 13 250 years ago with the City of Sherbrooke indicated, image of rocks with ridges indicating wear, image of a hole at an archaeological site near a river, stone artifact and striped arrow in soil, schematic image of a phosphate PO3- 4 element on which phosphorous and oxygen elements are indicated.
[A.C.] When archaeological searches are conducted, the evolution of the milieu and the soil cannot be ignored. In the Eastern Townships, and throughout all of North America, the determining factor is the retreat of the glaciers. The area was not habitable before this period. Deposits of all kinds, left by the glaciers, impacted the area’s geography and vegetation. The shores of lakes, oceans, and rivers affected human migration, determining the locations where artifacts can be found. Deposits also affected the nature of the soil, and thus the likelihood of finding preserved artifacts. Lastly, the soil's phosphorus content is an element that makes it possible to refine searches.
Clip produced by the Sherbrooke Museum of Nature and Science
Date: September 2018
Length: 6:54
An animated character, Éric Graillon, explains the role of soil analysis in the history of the area's suitability for habitation and the search for archaeological artifacts. The clip presents the chronology of the continental glacial retreat in Canada, particularly in the Eastern Townships.
