The polar position Hypothesis

This idea was suggested early on and said that ice sheets should appear on continents when they are located at polar, or near-polar, locations (high latitudes). If there were not any continents near the North or South Poles, then no ice should exist anywhere on Earth. This theory only takes into effect movement of the continents through plate tectonics.

While this theory has proven true for many demonstrated time intervals in the past, it has not always been true. Today is one example. There are ice age sheets at high latitudes (polar ice caps and ice sheets), that exist because of (1) cold temperatures caused by low angles of sunshine, (2) high albedoes (reflectivity) because of the snow and sea ice cover, and (3) adequate snow being added on a regular basis to the ice sheets. But there are also glaciers that exist in many other places in the world that are not at high latitudes.

During a time interval from 425 to 325 million years ago, land existed at the South Pole for almost 100 million years without any ice sheets forming. Although this is one hypothesis, it illustrated that there was more involved in determining cooling and warming periods than just the polar position of continents. It introduced the concept that there had to be other inputs necessary to explain large-scale glaciations. By experimenting with general circulation models (GCMs), it was proposed that periods of warmer climate were caused by elevated levels of CO2 in the atmosphere.

Several paleoclimatic studies concerning Pangaea support this theory. It has been determined that no ice sheets existed on Pangaea 200 million years ago, even though the supercontinent's northern and southern limits lay well within the Arctic and Antarctic Circles. These areas correspond with areas today like Greenland, which is ice covered. Because Pangaea did not have any polar ice, paleoclimatologists believe that Pangaea's climate was warmer than the Earth's climate is today.

Fossil evidence of trees dating back to the time of Pangaea also supports this theory. A variety of different palmlike vegetation grew at latitudes as high as 40 degrees. This could not happen today—winters would freeze them. Using evidence like this indicates that the Earth had a much more tropical environment at higher latitudes during this time period. This leads to a conclusion that the reason for a warmer Earth during this time period is that the CO2 level was much higher then than it is today. Many different climate models have been run using different thresholds of CO2 levels in the atmosphere and compared to the results of the geologic evidence from Pangaea. It has been determined that during this period the atmospheric level of CO2 was 1,650 ppm, nearly six times the level of CO2 before the Industrial Revolution (280 ppm).

Climate models also predict high aridity in the interior of Pangaea due to the high CO2 content. Geologic evidence also supports the model's predictions of widespread aridity. A major source of evidence is the existence of an extensive distribution of evaporite deposits. Evaporite deposits are salts that precipitate out of water that does not drain into the ocean. This occurs when evaporation is greater than precipitation. Because there is no outlet to an ocean, when the water evaporates, it leaves the salts behind as a deposit. A well-known example of this today is the Bonneville Salt Flats in Utah. It is a remnant of ancient Lake Bonneville, a large lake that existed from about 32,000 to 14,000 years ago. It occupied the lowest, closed depression in the eastern Great Basin and at its largest extent covered about 20,000 square miles (51,800 km2) of western Utah and smaller portions of eastern Nevada and southern Idaho. The lake eventually breached and drained during the last ice age. Today, the only remnants of this massive lake are the Great Salt Lake and the Bonneville Salt Flats.

The Salt Flats are massive evaporite deposits that extend for miles. They are extremely flat—one of the flattest places in the world. Geologists have determined that more evaporite salt was deposited at the time of Pan-gaea than at any time in the last several hundred million years. Because most of these deposits exist in what would have been the interior of the Pangaen continent, this gives climatologists valuable insight into what will happen to the interior areas of large continents if CO2 levels increase and global warming intensifies.

Paleoclimatologists also believe that the warmer climate of Pangaea kept the temperatures so far above freezing that any snow melted quickly, never accumulating long enough to allow glaciers to form.

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Responses

  • chilimanzar
    What is the polar position hypothesis?
    5 years ago
  • poppy
    What is polar position hypotthesis?
    6 years ago
  • MINNA
    Why the climate would be warmer on pangaea?
    5 years ago
  • zewdi
    What is polar positioning?
    5 years ago
  • dina
    How pangaea could have created warmer climate?
    5 years ago

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