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Roger Weller, geology instructor

Ice Age
Kaitlyn O'Rahilly
Physical Geology
Spring 2013

Ice Age 5: The Cause


            When “ice age” comes up in a conversation, it is most likely about the Ice Age movies. These movies confirm the stereotypes that people imagine when thinking about the ice age: giant mammoths, saber tooth tigers, and terrifying blizzards. The ice age is more than just a quadrilogy of cute 3D animated characters. The Ice Age movies may be poking fun at the real ice age, but there is a lot more behind the scenes action than 3D rendering.


            An ice age is a period of time when the Earth’s temperature decreases, creating continental ice sheets and glaciers. The picture below shows the glaciations of Earth over time in millions of years.


Earth has had four (or five) giant ice ages: the Huronian, Cyrogenian, Andean-Saharan, Karoo, and Quaternary. Some geologists claim we are still in an ice age, or consider one of the mini ice ages as a fifth (Quaternary). Over the course of billions of years, it is incredible that there has only been four-five major ice ages (that we know of), and only lasted millions of years. Also seen from the figure above, the ice ages are not spaced out evenly, or even lasting for the same amount of time. What causes the ice ages, and how do we know? There are hundreds of theories about how ice ages, or glacial ages, are formed.

Early geographers/geologists of the 18th century began studying the glaciers in Europe, discovering erratic boulders (former glaciers). This indicated that the glaciers had once been larger and longer. In the late 18th century, European geologists James Hutton, Goran Wahlenberg, and Jens Esmark all contributed to the earliest recognition of the ice ages. They all proposed a part of a theory that stated ice had once covered the entire Earth, and glaciers moved. These geologists were on the right track, but the Earth was never truly covered in ice, as speculated. Only about one third of the world was covered in ice. With modern technology, we can have a closer look at a realistic ice age. The pictures below are simulations of an ice age.




There are several astronomical theories. James Croll suggested that the Earth’s orbit caused ice ages. Milutin Milankovitch, a 1920s-1930s mathematician, proposed that the reason ice ages formed was based on the Earth’s axis and how much sunlight reaches the Earth’s surface. Milankovitch composed a mathematical formula to predict that ice ages would occur every 22,000, 41,000 and 100,000 years. These are called Milankovitch cycles. This seems legitimate if one is looking only at the most recent ice ages. Arthur Holmes stated that Milankovitch’s theory does not apply to the older ice ages. Other unlikely astronomical theories suggested ice dumps from space, or the Earth entering cold areas of space.


            The Continental and Crustal Displacement Theories proposed that the Earth’s land masses contributed to the ice ages. Arthur Holmes explains that the rotation of the Earth affected the Earth’s poles, thus changing their positions ever so slightly, creating drastic effects. Charles Hapgood agreed with Holmes and further suggested that the outer part of the Earth shifted position, while the inner remained untouched, shifting the poles. The Elevation Theory states that the landmasses and water level rose and fell, creating ice ages and warm climates throughout the years. Continental Drift is the theory proposed by Alfred Wegener, suggesting that the continental drifting brought continents to the colder regions of Earth, and then back down again to warmer regions. However, this does not explain why only certain areas on continents are glacially covered and other parts are not.


            Plate Tectonics is another theory. This theory proposed ocean circulation, changes in atmosphere, and changes in planetary albedo (reflected sunlight) created ice ages. Plate Tectonics suggested ice-albedo feedback systems were altered by surpluses of Carbon Dioxide and oceanic currents. The ice-albedo feedback is positive for snow, meaning that it will continue to reflect 85%-90% of sunlight until there is change in the environment. Did ocean currents really have such a drastic temperature/composition change that it affected one third of the entire world? Did giant meteors fall from the sky and change the atmosphere? All is possible, when looking back millions of years. Below is a picture explaining albedo in normal and glacial areas on Earth.


            The previous theories are the most well-known and accepted for the causes of the ice age. However, that does not stop one from speculating. J.W. Humphreys claimed that volcanoes could be changing the temperature. Super volcanoes could cause a dramatic atmospheric change, but not small ones that erupt every couple decades. Michael Oard proposed that there is only one ice age, however that does not explain the gaps in between the glacial periods. Escher von der Linth and Desor proposed that the tropics of Africa had once been a desert, changing the albedo for Africa, allowing ice sheets to form. Another theory proposed that the oceanic currents controlled the circulation to the northern glaciers, and when warm water stopped circulating, the ice ages began. The Greenhouse Effect proposed humans’ pollution trapped sunlight in that was supposed to be reflected back, slowly but steadily ending the ice age we are currently in. The Genesis flood theory stated that a great flood wiped out thousands of plants and animals, allowing mountains to elevate and moisture to accumulate in the atmosphere, creating a cooler climate and the beginning of the ice age.

            The ice age is a mystery to us today. Even when we think we have found the causes of an ice age, there is always evidence against it. Starting from the late 1700s, we knew that giant sheets of ice and glaciers once covered the world. Geologists, scientists, geographers, and ecologists all wonder what starts and ends an ice age. Did super volcanoes, Plate Tectonics, or Continental Drift cause the ice ages? Is the atmosphere to blame? Are humans ending the current ice age, or starting a new one? Can a mathematical formula predict the next ice age? Is a supernatural force controlling everything from above? Maybe all the theories combined are correct, or perhaps everything we studied is wrong. Eventually, either our ‘ice age’ will end, or a real ice age will begin. Nature has had ice ages for millions of years, and will continue to have more in the future. We will never know exactly what caused the ice ages because no one was around to see them. With the expansion of technology, an accepted Ice Age Law is soon to emerge…as well as Ice Age 5, the movie.

Sources: Excellent!