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Ice Age - Geology

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The ice age is a simple geologic time scale in which the ground was covered with thick sheets of ice. The ice age geologic time scale is also known as the glacial age and such periods of large-scale glaciation lasted for several million years. There have been a number of major ice ages throughout the geological history of the Earth. The earliest known Ice age was the Precambrian Ice age which was about 570 million years ago and the most recent one was the Pleistocene Epoch Ice Age which was about 2.6 million years ago. The Ice age geology affected and reshaped many of the landmass features of the continents. 


The Ice Ages and Its Characteristics

According to geology, an ice age is a long period of reduction in the temperature of the Earth’s surface and atmosphere which results in the presence of or expansion of continental and polar ice sheets and glaciers. There have been four major geologic events of ice age geology in the geological history of the Earth. They belong to the periods of Huronian, Cryogenian, Andean-Saharan, the late Paleozoic period.


The Ice age is a period of the alternating cycle of events of temperature changes in the climatic conditions. They are the periods of ice age geology to greenhouse geology, during which there are no glaciers or ice sheets on the surface of the earth. Currently, the earth is in the Quaternary glaciation period which is more commonly known as the period of the Quaternary ice age. The current Quaternary ice age started approximately 2.6 million years ago at the beginning of the current Quaternary Period of the current Cenozoic Era when the ice sheets began spreading in the Northern Hemisphere.


Ice age, according to the glaciology terminology, is the period when extensive ice sheets cover both the northern and southern hemispheres. Going by this definition we are in the Holocene period which is an interglacial period (an intermittent warm period within an ice age). The extent of the ice sheets spread over the surface of the Earth is not retained over the full interval. And as pointed out earlier, the Ice age geology affects and changes the shape of the surface of the Earth. Many times certain evidence of prior ice sheets are removed by the later ice ages. Ice age rocks are also weathered down by the scouring action of each of the glaciations. 


Evidence and Reasons for the Ice Ages


Evidence of the Ice Age Geologic Time Scale

There are three main sources that provide evidence for the existence of the ice ages. The three types of evidence are geological evidence, chemical evidence, and paleontological evidence.

  • Geological Evidence: 

The geological evidence is provided majorly in the form of the remains of the weathering from the washing off of the ice age rocks, glacial moraines, valley cutting, drumlins, etc. Usually, subsequent ice ages destroy any evidence of the previous ice age geology which was problematic for earlier geological studies determining the ice age geologic time scale. With the study involving sediment and ice cores, it was possible to get more accurate information about the ice age geologic time scale. An example of this is the revelation of the true situation that the glacial periods are long, and interglacials are short, which was not claimed previously.

  • Chemical Evidence: 

Much of the chemical evidence for the ice age geology comes from the ratios of the isotopes in the fossil records present in the sediments, sedimentary rocks, and ocean sediment cores. Based upon the chemical composition of the isotopes present in the ice cores and the bubbles of air a temperature record was constructed.

  • Paleontological evidence: 

The geographical distribution of the fossils provides the basis for the paleontological evidence of the ice age geology. An example is the phenomenon of animal locomotion. During the peak of ice age periods when ice sheets cover most of the land surface, the cold-weather animals come down to the lower altitudes from higher elevations. Also, as the ice age starts spreading, the hot-weather animals come down to the lower elevations to save themselves from colder temperatures.

Although there have been difficulties, the analysis of the ice age cores and ocean sediment cores provide one of the most credible records of glacial and interglacials over the past million years.


Cause for the Ice Ages

The reason for the Ice Ages is not clearly known and understood but there are a number of factors that are thought to have contributed to the ice age geology. The consensus for the factors leading to the occurrence of ice age geology is atmospheric composition - such as the concentrations of carbon dioxide and methane (both are greenhouse gases), changes in earth’s orbit around the Sun known as Milankovitch cycles, the motion of tectonic plates that resulted in changes in the relative location and the amount of continental and oceanic crust which affected the wind and ocean currents, variations in solar output, the orbital dynamics of the Earth-Moon system, the impact of relatively large meteorites and the activities of volcanoes and supervolcanoes. 


One of the factors of variations in the earth’s orbit or the Milankovitch cycles is the cyclic variations in the characteristics of Earth’s orbit around the Sun, which enforces the changes for the Ice Age occurrence over a period of 1,00,000 years. An example of this is the Pleistocene Epoch ice age involving a period of both the early and late Pleistocene ice age map on the ice age geology timeline. The late Pleistocene ice age map is suggested as a jump in-between three quasi-stable climate states. These jumps are induced by the orbital forcing or changes in the orbital variations of Earth around the Sun. 


The Current Quaternary Ice Age

The Quaternary ice age is the current phase of the geologic time-scale. The Quaternary period ice age is also known as the Pleistocene Epoch ice age. The Quaternary ice age timeline started approximately 2.6 million years ago and is a series of alternating glacial and interglacial periods. Since there are ice sheets yet present on the poles, it is believed by geologists that we are currently in the Quaternary ice age with an ongoing interglacial period. In popular culture, the ice age is generally referred to as the most recent of the Pleistocene Epoch ice age.

FAQ (Frequently Asked Questions)

1. When was the Last Ice Age on Earth?

Ans: The last ice age when Earth’s surface was surrounded by ice sheets occurred about 2.6 million years ago and lasted till 11,700 years ago. It occurred during the Pleistocene Epoch of the geologic time-scale of the Earth. Since there are ice sheets present at the poles, many geologists believe that the Quaternary ice age of the Pleistocene glaciation period is still ongoing with Earth experiencing an interglacial period. 

2. What Causes an Ice Age?

Ans: There are various factors that are agreed upon by the geologists as factors that lead to the ice age. One such factor is continuing lower summer temperatures in the Earth’s atmosphere. When the summer temperatures of the northern hemisphere do not go above freezing for years, it is said to trigger an ice age.