ancient Michigan basin area and discuss a brief geological history of the area and how the mammals that lived during the Ice Age adapted to their environment over the years.
Use at least 12 sources of information; use quotes
Michigan experienced the great Ice Age and was covered by glaciers several times. These events in turn affected the mammals that inhabited what are now the Great Lakes region and the state of Michigan.
Mammals of Michigan
History of Ice Age Michigan
Twenty thousand years ago, mile-thick glacial ice sheets that extended from Canada to the Ohio River covered Michigan and most of northern North America. It took more than 12,000 years for the ice to melt, leaving Michigan a glacially scarred landscape with the Great Lakes. Four huge continental glaciers that formed over the Midwest eventually formed the state's features. The last one known as the Wisconsin Glacier occurred about 14,000 years ago. This mass of ice swept across almost four million square miles, dragging millions of tons of earth and rocks over the landscape.
In addition, Michigan geology is also characterized by a major horizontal break-bedrock geology vs. surficial geology. Mush of the state is veneered by deposits of Pleistocene age, the results of glacial and glaciofluvial depositional processes. These sediments are unconsolidated tills, gravel, sands, silts and clays. They effectively mask much of the bedrock geology, particularly in the Southern Peninsula. With a few exceptions, the spectacular metallic mineral deposits for which Michigan is justly famous occur in rocks of Precambrian age. The younger Paleozoic rocks are by no means devoid of mineral deposits or occurrences, but their variety is smaller and their mineral assemblages are more severely restricted.
We've learned from Michigan's geology and fossil patterns that Michigan was not always underwater. The oldest known vertebrate fossils are Devonian fish, such as the placoderms and primitive sharks. There are also fossil land plants from the Devonian and Mississippian periods, more than 300 million years old. Other fossils such as the lungfish burrows from the Pennsylvania Period also indicate that there was dry land 280 million years ago.
As the climate began to warm, soil and rocks were carried away from the melting glacier, creating low-lying hills across the terrain. As this mix of pebbles, stones, soil and boulders dried, they formed a mixture of sand, silt and clay. As the glacier continued to disappear, plants began to appear on the drying landscape. The glaciers disappeared and never returned. They had carved and shaped the landscape as the climate began to dramatically change. As the glaciers created hilly belts, rolling plains and uplands, the retreating ice blocked drainage channels creating the many lakes, swamps and marshes that characterize modern day Michigan.
What is initially interesting to note about Michigan is that it is divided into two areas, the Northern and Southern Peninsulas and that these two areas are geographically separate. These two areas also exhibit different bedrock that identifies the western part of the Northern Peninsula as Precambrian and Cambrian and the eastern part coupled with the Southern Peninsula as younger, dating to the Ordovician to Pennsylvania periods.
The area's bedrock is Paleozoic bedrock deposited in marine and near-shore environments. This Paleozoic bedrock was deposited in a crater basin, known as the Michigan basin, which was occupied by marine waters from the Silurian through Pennsylvanian Periods. Mississippian and Devonian bedrocks are nearest the surface in the south and along the Great Lakes shorelines; Pennsylvanian bedrock is near the surface in the north (at the center of the Michigan basin).
According to the Michigan Department of Environmental Quality, Geological Survey Division, "within Michigan, the oldest Precambrain rocks have been subjected to at least three major periods of crustal deformation and mountain building and to at least three to four additional major or minor deformational episodes. Metamorphism of varying degrees of intensity accompanied many of the disturbances and transformed sedimentary, intrusive igenous and volcanic rocks into their metamorphic equivalents. Thus basalt became greenstone; granite became granitic gneiss; sandstone was converted to quartzite; limestone to marble and shale became slate or mice schist."
The Paleozoic rocks of Michigan do not represent a completely continuous record of Paleozoic sedimentation. At several times uplift interrupted the general sinking of the basin and erosion, or at least nondeposition, characterized that particular time interval. Thus, the stratigraphic sequence contains time gaps, some local and some regional, e.g., in the Early Ordovician, the Early Devonian and the Late Mississippian Periods. The post-Pennsylvanian geological record for Michigan is divided into two main parts: "the lost interval," a nearly unrepresented period of time between the end of the Pennsylvanian and the youngest Pleistocene glaciation, and the Pleistocene glacial epoch. Missing are the rocks of the youngest Paleozoic Period (Permian), nearly all of the Mesozoic Era (Triassic, Jurassic and Cretaceous) and all of the Cenozoic, except for the Pleistocene. The complete Pleistocene Epoch involved four major glacial periods, but only deposits from the youngest, the Wisconsinian, are represented as surficial deposits in Michigan.
Looking back even further in prehistoric Michigan's history, during the Devonian Period, some 350 million years ago, Michigan was believed to be near the equator. The area was covered with warm and shallow seas that contained coral reefs. Eventually, the coral became fossilized, producing what is now known as Michigan's state stone -- Petosky Stones.
The stone is found only in the rocks from the Gravel Point Formation. This Middle Devonian (345-395 million years ago) limestone formation only outcrops near Petosky, which is near the northern tip of Michigan's Southern Peninsula. Ice Age glaciers gouged Petoskys from the bedrock and spread them far and wide.
Most Michigan fossils represent either the ancient Paleozoic Era or the recent Pleistocene Epoch or Ice Age. Actually, Michigan's oldest fossils predate the Paleozoic Era. Algal stromatolites -- fossils of plantlike creatures called algae -- found in the Canadian or Laurentian Shield in northern Michigan date back to the middle of the Precambrian Era.
In early 2000, an ABC News article highlighted a forest that was found in Michigan's Upper Peninsula that was underwater. The belief is that fast melting ice and sand drown the spruce trees and unintentionally preserved them. The wood was prevented from rotting by the rush of fine-grained sand and this precipitated fossilization. According to Professor Kurt Pregitzer, University of Michigan Forestry Department, "it looks very much like a forest you would find today near Hudson Bay." Based on the preliminary evidence, the scientists believe that the sudden and dramatic changes that took place climactically were not always detectable in advance. This may be an indicator of why some mammals became extinct.
Mammal and Ice Age Environmental Factors
There are many theories as to why certain animals became extinct during the Ice Age and why others adapted and often mutated to survive as their environment changed. More than 15,000 years ago, giant animals roamed North America, including what is now Michigan. During the late Pleistocene Era, which is during and after the last ice age, many mammals became extinct.
The last time glaciers covered large parts of North America was from approximately 132,000 years ago until 10,000 years ago. Changes in climate account for the advance and retreat of the glaciers. Because the late Pleistocene extinctions occurred so long ago and involved so many species, it is difficult to be accurate about exactly when they occurred, but it appears that they occurred when the glaciers were retreating. Many archeologists believe the extinctions occurred about 12,000 years ago.
The end of the Permian Period (280 to 230 Million years ago) witnessed the extinction of a large number of species. This event is often called the Permo-Triassic Boundary. The Permian Extinction was one of the largest extinction events in geologic history, with approximately 50% of all animal families going extinct. It is estimated that 85-95% of marine species, 70% of all terrestrial species and many tree species went extinct in less than one million years.
It is often theorized that humans, who entered the area about 12,000 years ago in search of food, may have hunted many of the mammals into extinction. Michigan's original inhabitants arrived 11,000 years ago, probably in search of food after the glaciers had melted. Archeologists believe that throughout the next 10,000 years groups passed through the region, settling in villages for a while and then moving on. These prehistoric settlers are referred to as Paleo-Indians (approximately 11,000 years ago), the Old Copper People (approximately 8,000 years ago) and the Mound Builders (approximately 3,000 years ago).
The coincidence that humans arrived about the time that many of the animals became extinct provides an explanation for the extinctions that occurred during this time.
Known as the "Pleistocene overkill hypothesis," argued since the 1960s by Paul S. Martin, a researcher has states that the mammoths had lived in North and South America for a long time before the arrival of humans around 12,000 years ago. He believes strongly that the rapid colonization by big…
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