Helping Children Understand Geologic Time and Changes to the BiosphereCertain central principles reoccur throughout prehistory and should be noted as patterns.
For example, when the climate is warm and there is little or no glacial ice, sea levels are high and there are many shallow marine habitats. A high level of tectonic activity with its large undersea mountains increases sea level as well. When glaciers and ice caps form, sea level drops and the continent shelves are exposed.
Land masses that were separated by shallow oceans may be connected by dry land when the sea level is low, and shallow marine habitats are more restricted. When continents are separate there is much more coastline than when they all are joined.
The tidal zone for organisms to inhabit is more extensive. When continents are joined, the interiors can be quite dry and have large temperature extremes. When mountains rise, the area downwind from them may have a “rain-shadow” effect and be much drier.
The position of the continents on the planet changes their climates. The Phanerozoic Eon began with the land masses, including the future North America, in the Southern Hemisphere. North America didn’t move totally into the Northern Hemisphere until the Jurassic Period. It has spent quite a lot of time in the tropics.
Paleogeographic maps help children understand the climates of the Earth through the ages. When there is land at the poles, this may promote more ice accumulation. The latitude of land masses can affect whether land masses have a dry climate or a moist, warm one. Generally, land near the equator is very warm, but at times in Earth’s past, even land near the Arctic and Antarctic Circles has been warm and at other times, land in temperate latitudes has been ice-covered. This tells us that the average global temperature is also an important factor.
Read much more in An Outline of Geologic Time and the History of Life, Written by Priscilla Spears, PhD. Published March 2010 and revised July 2010.