Evidence and Potential Causes of Ice Ages

  The theory of Ice Ages was first proposed after the discovery of evidence of glaciers (rocks, sand) in areas that do not traditionally have these elements. This “till” was caught up in the motion of the glacier and left behind at a different location (Source 1). Additionally, glacial movement left behind polished and striated bedrock pavement, altered landscapes, and carved rock (Sources 2 and 6).

  There is one large question that scientists cannot establish a definite answer to; how do Ice Ages come about? The theories break down into two major categories Terrestrial and Extraterrestrial.

  The first of the terrestrial theories relates to the presence of mountains and low sea levels. The natural process of uplifting continental blocks creating height fluctuations on the earth’s surface has some affect on the climate through alterations in wind and water patterns. (Source 2 and 4). Additionally, the opening and closing of gateways for ocean currents has the potential to isolate polar regions resulting in rapid growth of ice sheets and temperature inconstancies on the earth. Each of these is a result of plate tectonics either pushing together or pulling apart. A second theory is volcanic ash and dust could reflect the sunlight out of the earth’s atmosphere resulting in a cooler climate (Source 2). The third terrestrial theory is related to carbon dioxide. Plate tectonics have the potential to reduce atmospheric carbon dioxide virtually reversing the greenhouse effect (Source 4).

  The first extraterrestrial theory is that variations in the moon and the sun can periodically change the earth’s orbit, isolating portions enough to cause glacial formation. This theory was later altered to be what is the most likely cause (Source 2). It proposed that the sun varies according to three factors. The first is that the earth spins on its axis un-evenly up to 23.5 degrees to either side. This results in a variation of season strength. Secondly, this wobble takes 41,000 years to make a full rotation (left to right then back to the middle) providing a lot of time where one hemisphere is further away from the sun that the other (Source 5). Finally, there is a change in the earth’s orbit every 100,000 years to a more elliptical pattern moving it further away from the sun for up to 23,000 years. The final extraterrestrial theory relies on an ice dump from outer space (Source 2). Evidence comes from the fact that all major Ice Ages have occurred when these three inconsistencies occur at the same time (Source 5).

Picture courtesy of Source 4 NOVA.