Ice Age
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The book I chose to read is Frozen Earth: Explaining the Ice Age by R. V. Fodor, the associate Professor of Geology at North Carolina State University. It presents the recent discoveries and history of the ice age in an easy-understanding and accessible way. He first begins with a little background of ice ages. He then talks about glaciers and how they form and act. Then he talks about the different theories of how this happened. He concludes with speaking of the future and the climate it possesses.
Scientists have discovered that in the past million years, glaciers have covered the Earths surface on several different occasions. There have been several “ice ages” in the Earths past, and twenty thousand years ago was Earths most recently recorded. Large blankets of ice covered a large majority of land, forcing man and animals southward. Much of North America was under ice. Seven-thousand years ago the glaciers had melted off and that marked the end of it. Because of the glaciers being such ancient history it is hard for scientists to obtain and interpret data. The study of glaciers and the ice age is relatively new. In Switzerland around 1800, rocks attracted geologists in developing the first ideas of the ice ages. They wondered why large smooth boulders, called erratics, were lying out of place in fields and forests. Charles Lyell argued that icebergs had placed them there. Two other scientists stated that the boulders in the valley floors were similar to those found in the glaciers of the Alps. Louis Agassiz, a Swiss scientist, proved that ice could do this. He showed other scientists of places where large moving ice sheets had scratched and carved the surface of valley walls and floors. He was finally able to prove to the scientists that there had been an ice age. All of many doubts that ice sheets could occupy such large areas of land, were silenced after an expedition to Greenland in 1852. Furthermore, in the 1850s scientists proved that there had been more than one period of colder climates followed periods of warmth. It was believed by the twentieth century that up to four ice ages had occurred during the last million years.
Glaciers are large masses of ice. The north and south poles of the globe are covered with snow and ice year-around. These areas with year-around snow are said to be above the snowline. The elevation of a snowline above sea level varies depending on the amount of heat present and the amount of snowfall a certain area receives. Ice glaciers form not only from the freezing of water but also by compaction. The best example of this is; when you balled up some snow when you were a kid and compressed it into a snowball to throw at your friend. Over hundreds of years of built up snow, glaciers form and begin to grow slowly down hill like molasses. These glaciers move from a few inches a day to rarely a couple yards a day. There are glaciers on every continent except Australia. There is actually a glacier the size of the entire United States in Antarctica. In some places it is deep as one mile! An interesting fact about glaciers; there is enough ice in the world to cover all the land in the world and the sheet would be 400 feet deep! They move like rivers through valleys. The top portion of glaciers moves faster than the bottom portion that scrapes and drags on the surface. Scientists discovered the speed of a glacier at the top of Mt. Blanc in Switzerland from the tragic burial of an entire climbing team. Fourty-one years after, there bodies were found ten-thousand feet away at the foot of a glacier. The bodies had moved eight inches a day. Glaciers move relatively slow, but there has been cases of glaciers moving rapidly out of control. The speed depends on the amount of snow being applied to the source of the glacier. Geologists focus on the rocks and moraines at the mouth of the glaciers that have been scoured and carved by the ice. The evidence is highly informal, but the cause of the ice ages has yet to be discovered. However, there has been many educated theories of why the ice ages took place.
The cause of ice ages must explain why the Earths climate was relatively colder during periods of the Earths history. Scientists first looked at the sun for the answers to the ice age. They also thought that volcanoes could have caused the glaciers. When volcanoes erupt, they produce a large area of dark smoke in the air, blocking out the sun. Could many eruptions cause black layers of smog large enough to block out the suns heat triggering the formation of glaciers? It is possible, but modern scientist have found no evidence of that caliber of volcanic eruptions in the Earths past. Scientists also looked at the history of sunspots. There was a period in Earths history of no sunspots, causing the temperature to drop. It was also believed that the sun moved through large areas of dust in the solar system, causing the Earths climate to change. Both of these theories are possible, but cannot be proved or tested. No explanation for ice ages has received more attention than one based on how the earth travels around the sun and spins on its axis. Hipparchus discovered that the earths North Pole has not always pointed the same direction in space. What Hipparchus determined 2000 years ago was that the earths axis “wobbles”. The top of the earth moves, drawing an imaginary circle in space. At one time the Earth can tilt away from the sun. This movement is called axial precession and it takes about 22,000 years to complete the circle. What he didnt know is that the wobble effects climate. This set the background for the only theory proven to be a cause of ice ages: the astronomical theory. Johannes Kepler made a striking discovery about how the earth travels around the sun. The earths orbit around the sun is not a circle, but an ellipse. Two centuries later, a French astronomer Urbain Leverrier, discovered that the shape of the orbit gradually changes over thousands of years. It changes from an ellipse to a circle. The amount of elongation in the orbit at any time is called the orbital eccentricity. In the 1800s, James croll showed that the change in the earths orbit from high to low eccentricity is approximately every 100,000 years. The orbit is in a period where it carries the earth unusually far from the sun for part of each year. Croll combined the 22,000 year axial precession cycle with the 100,000 year orbital cycle to account for cooler climates, causing the ice age. Through his calculations, he showed that over the period from 80,000 to 250,000 years ago, the Northern and Southern hemispheres had many alternating ice ages and warm periods. His theory appealed to many scientists, but met defeat because some glacial tills