When there is a prolonged decrease in the Earth’s temperature, large sheets of ice cover vast lands.
The geological history of the Earth characterizing polar ice sheets and alpine glaciers is known as the Ice Age.
Throughout history, the Earth has gone through various phases of the ice age and greenhouse periods, the latter characterizing a period where no glaciers exist on the planet.
During the Ice Age, the snow is prevented from melting into the water due to the drop in the temperatures. This causes the lowermost layer of the precipitation to become ice and the subsequent weight of the accumulated snow slowly moves forward resulting in what is known as a glacier.
The ice and snow trap the earth’s moisture in a cyclical pattern leading to the rapid expansion of the ice sheets and consequent decline of sea levels.
Scientists agree that there have been over 5 ice ages in the last millions of years. They also say that in the 4.6 billion years of Earth’s history there may have been close to 11 ice ages.
The largest ice age covered one-third of the Earth’s surface resulting in the extinction of several species. Such long periods of polar ice sheets can drastically change the geography of entire continents.
Scientists have been able to date the first Ice Age to more than 570,000 years ago. It took place during the Precambrian Time.
The last massive ice age is said to have taken place between 2.7 million years ago and lasted till 11,700 years ago. It is called the Pleistocene Epoch.
The Ice age is characterized by very scant vegetation, glaciers and large expanses of lands covered with snow which can sometimes be thousands of feet thick.
Scientists like Louis Agassiz and Milutin Milankovitch have played an instrumental role in determining the causes of the ice ages.
They explained that the different cycles of the Earth’s Orbit and the moving of the tectonic plates underneath the surface of the Earth trigger the increase or decrease in temperatures.
The Ice Age is also known as the Glacial Age and we are currently in a period known as the Holocene.
How did we Discover it?
Various studies by prominent scientists led to the discovery of the Ice Age. The first one in Europe began with an expedition in the valley of Chamonix.
Pierre Martel in 1742 reported that the residents of the town in the Alps of Savoy believe that the ‘erratic boulders’ found in the location are a result of glaciers. Erratic boulders are rocks totally different from the ones that are naturally found in the region.
In Switzerland, there were other scholars and scientists that offered very similar explanations for the presence of the boulders like Jean de Charpentier and Johann Wolfgang von Goethe.
Bavarian naturalist Ernst von Bibra attributed the presence of debris also known as glacial till in the Chilean Andes to the movement of glaciers.
Slowly the discussions spread to many parts of Europe, in 1818, a botanist from Sweden called Goran Wahlenberg wrote the theory of glaciation of the Scandanavian Peninsula while a Norwegian geologist called Jens Esmark developed his theory of the sequence of ice ages worldwide.
In Esmark’s paper of 1824, he pinpointed the changes in the Earth’s orbit and the consequent changes in the climate on Earth as the causes of glaciation. Albrecht Reinhard Bernhadi was influenced by Esmark’s paper.
Apart from these developments, several other engineers and scientists had collaborated to study and research the presence of erratic boulders in Europe, the mosses that grow on them, and the possible ways in which they were transported.
Ignaz Venetz was a Swiss civil engineer. He along with his friend Jean de Charpentier developed a theory of glaciation limited to the Alps. In 1834, they presented it to the Schweizerische Naturforschende Gesellschaft.
Soon Karl Friedrich Schimper joined Jean de Charpentier along with Louis Agassiz and they developed the theory of sequence of glaciations. Schimper called the period of glaciers ‘ice age’.
After several expeditions and researches, the theory was accepted by scientists. It was accepted internationally after the publication of James Croll’s work in Climate and Time in 1875.
The scientists based their studies and researches on the geological evidence from the sites. Scratching on the rocks, presence of debris in the area, unusual or erratic boulders, valley cutting, etc.
Scientists also used the chemical evidence found in the form of ratios of isotopes in the fossils. Water with denser isotopes evaporates faster with higher temperatures than lower. The atmospheric samples which included bubbles of air helped in the construction of a temperature record.
The study of fossils also aided the discovery of the ice age because of the patterns in which the fossils were distributed. The animals that preferred colder climates moved southwards pushing the animals adapted to warmer climates into the lower latitudes.
Types of Ice Age
The Earth is said to have had at least 5 massive ice ages in the Earth’s history, namely, Huronian, Cryogenian, Andean-Saharan, Late Paleozoic, and the Quaternary Ice Age.
The longest of the ice ages is the Huronian Ice Age which was formed about 2.4 billion years ago. Various rocks, glacial till, varves, outwash, etc. near Lake Huron are evidence of this time.
This ice age is said to have taken place due to the shortage of atmospheric methane during the Great Oxygenation Event.
The Cryogenian ice age was probably the most intense in the last billion years and has been well researched.
Scientists suggest that between 720 to 630 million years from now, the Earth may have been fully covered with glacial ice sheets extending all the way down to the equator.
The Earth may have looked like a snowball during the Cryogenian Period before warming down due to the presence of greenhouse gases like CO2 in volcanoes.
The Andean-Saharan ice age happened from 460 to 420 years ago. Its evidence is found in West Africa, Arabia, Sahara, South Amazon, and the Andes.
The late Paleozoic was the result of the evolution of land vegetation and is also known as the Karoo glaciation because the geological evidence was found in the Karoo region of South Africa. The increase in oxygen and decrease in CO2 resulted in the late Paleozoic Icehouse.
The Quaternary Ice Age began when the Northern Hemisphere was covered with ice around 2.58 million years ago.
The ice sheets have been expanding and shrinking since the interval of 40,000 to 100,000 years which are also known as glacial and interglacial periods as well as glacial advances and glacial retreats.
We are now in an interglacial period with ice sheets present only in Greenland, Antarctica, and Baffin Island.
Why does the Ice Age Happen?
Though the causes are not fully understood by modern scientists, a wide range of factors is said to play a critical role in the formation of the ice ages.
The reduction of greenhouse gases from the environment leads to cooling periods while the increase in greenhouse gases lead to warmer temperatures, this may have triggered the various phases of the ice age.
The moving of continents and volcanism are said to have affected the release of greenhouse gases in the Earth’s atmosphere.
Geologists say that when the flow of warm water is blocked from the equator to the poles, ice sheets begin to form. The surface of the ice sheets reflects the sun’s rays which further reduces the absorption of solar radiation.
The ice age intensifies until greenhouse gases are released to trigger warming of the ice sheets and better absorption of the sun’s radiation.
We are currently said to be in an ice age because our present geographical positioning meets the criteria of an ice age.
There is a continent that is placed at the pole called Antarctica, a landlocked polar sea that exists as the Arctic ocean, and the existence of a supercontinent near the equator like present-day Eurasia.
Scientists believe that a major factor in the current Ice age is the Himalayas. It was formed due to tectonic shifts and the collision of the Indo-Australian Plate and the Eurasian Plate about 70 million years ago.
These mountains have caused an increase in the Earth’s total rainfall which has led to the reduction of the greenhouse effect due to the eradication of carbon dioxide from the Earth’s atmosphere.
The ocean currents also play a vital role in the way the temperatures on Earth get affected. The ocean currents change with the position of the continents, sea levels, and salinity.
Volcanic activity is a key factor that can lead to changes in the atmosphere over time leading to ice ages. The carbon dioxide from the volcanoes may have contributed to the highest temperatures.
The orbit of the Earth can also play a significant role in the forming and ending of ice ages. The closer the Earth is to the sun, the hotter it gets.
The slightest variations in the axis of the Earth’s orbit can affect solar absorption over time and lead to changes in climate. The Milankovitch cycles describe the variations caused by the Earth’s Orbit around the sun.
Scientists have found sufficient evidence to link the Milankovitch cycles to the glacial and interglacial periods in an ice age.
The lower energy output of the sun has also been narrowed down as a possible cause for ice ages to form. Similarly, the axis of the Earth can affect its energy absorption if it tilts in different ways.
Life in the Ice Age
Animals have adapted themselves to live in the different climates that the Earth provides. However, changes in climate also bring about the extinction of the animals that cannot adapt to the changing environment fast enough.
Many animals of the ice ages resemble the animals we find today. Some of them were unusually large and quite a few of them are completely extinct.
Fossils found in the Americas reveal the presence of a cat with two very large canine teeth on the upper jaw. This cat is called the Saber-Toothed Cat because it could stab its prey with its strong upper jaw and tear very thick skin like that of a rhinoceros.
The woolly mammoths were plant-eating mammals with some resemblance to the present-day Indian elephant. Their body was covered with thick and dense hair and underfur. The tusks were curved and were used for digging the ice for grass.
Glyptodon was a type of large armadillo. It was herbivorous and about the size of a small car. It had no front teeth but its powerful jaws had a set of grinding teeth at the back. It was shaped like a dome and had body armor covering its tail, head, and back.
The woolly rhino or Coelodonta is closely related to the rhinos of the present-day. There were two horns on the wooly rhino’s snout, one smaller than the other. It was about 11 feet tall and ate plants. It had a stocky body with short and thick legs. It had a very hairy skin and small ears.
The Giant short-faced bear lived in Alaska and was bigger than any bear of the present time. It was a carnivore and ate small as well as large prey. It had a powerful jaw and a huge head. It was taller and leaner than the grizzly bears and did not gain weight during the winter.
The Steppe bisons did not look like the bisons of America and Canada. They looked more like cows and ate a variety of different grass. There were more steppe bison fossils found in Alaska than any other animal that lived there during the ice age.
The cave lion was one of the largest lion species to have evolved in history and was about 10% larger than the present-day lions. It is depicted in the cave paintings with stripes and some fur around the neck.
It was called the cave lion not because it lived in caves but because it preyed on cave bears.