Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
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.
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.
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.
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.