What Is An Ice Age?
The term ice age is used to refer to a period of time in which the earth experiences colder temperatures on average. These cold temperatures result in the growth and expansion of glaciers and ice sheets around the globe. Ice ages may last for millions of years and when they end, the earth begins experiencing warmer temperatures once again. Scientifically speak, the world experiences an ice age any time ice sheets are present over the extreme points of the northern and southern hemispheres. According to this definition, the earth is currently in the midst of an ice age and has experienced at least five over the course of history. This article takes a closer look at each of these 5 ice ages: Quaternary, Karoo, Andean-Saharan, Cryogenian, and Huronian.
How Many Ice Ages Have Been Recorded?
The Quaternary Ice Age, also known as the Quaternary Glaciation, is the ice age that is currently being experienced by earth. This period of glaciation began approximately 2.58 million years ago and is characterized by the expansion of ice sheets over both Greenland and Antarctica. As these ice sheets have grown, the amount of sunlight reflected back into the atmosphere has also increased, resulting in cooler temperatures across the globe. Several theories exist to explain why the Quaternary Glaciation period has occurred. These theories include everything from the influence of ocean currents to tectonic plate activity.
One thing is certain, the current ice age has had a massive effect on the general geography of the surface of the earth in less time than previous ice ages. The erosion and sedimentary deposits caused by these glaciers has been instrumental in the creation of large mountain ranges, deep river valleys, and lakes and rivers. It is believed that this ice age has resulted in more lakes than any other ice age in the past.
The Karoo Ice Age took place sometime between 360 and 260 million years ago and was initially recorded during the 1800’s. During the earliest part of this ice age, scientists believe that ice sheets grew from the southern region of both present-day Africa and present-day South America. Most theories of how this ice age was first created are primarily rooted in the knowledge that plants on land began to undergo significant evolutionary changes during this time. As these plants grew to immense sizes, they worked to reduce the levels of carbon dioxide and increase the levels of oxygen in the atmosphere. As these changes occurred, the summers were not warm enough to melt the ever-increasing ice sheets around the world.
The major effect of the Karoo Ice Age is often cited as the increased evolution of plants and animals during this time. As oxygen levels increased, animals began to experience changes to their metabolic systems. As a result, large vertebrate (both land roaming and flying species) were able to evolve.
The Andean-Saharan Ice Age, also known as the Andean-Saharan Glaciation, took place between 450 and 420 million years ago. Its name is drawn from the pattern of glaciation that occurred during this time. Researchers believe that ice sheets began to form over the present-day Sahara Desert across Morocco, West Africa, and Saudi Arabia between 450 and 440 million years ago. As the temperatures continued to drop, ice sheets were later formed over present-day South America, across the Amazon region and into the Andes Mountains. The majority of the ice and glaciers were concentrated over Africa and the eastern region of present-day Brazil. Because of its short duration, many geologists consider the Andean-Saharan Ice Age to be a minor period of glaciation.
Geologists have not yet reached an agreement as to how this particular ice age occurred. This lack of consensus is largely due to the conflicting data collected from this era. For example, researchers agree that the strength of the sun was weaker at the beginning of this time period and that this weakened solar energy could possibly prompt a period of glaciation, given the right circumstances. At this time, however, the amount of carbon dioxide in the air was at extremely high levels and carbon dioxide is known to be a greenhouse gas that generally contributes to rising temperatures on earth.
The Cryogenian Ice Age is recorded to have taken place between 720 and 635 million years ago, making it the second oldest period of glaciation known. This glaciation event occurred during the Neoproterozoic Era, which happened before the Ediacaran Era. Within this span of 85 million years, the earth experienced its two coldest times: the Marinoan Glaciation (which lasted for 15 million years, between 650 and 635 million years ago) and the Sturtian Glaciation (which lasted for approximately 74 million years, between 717 and 643 million years ago). Many scientists believe that during these two particular periods, the entire earth was covered in ice. A differing theory, however, suggests that an area of ocean located near the equator was left only partly frozen. The academic community has still not reached an agreement about how the Cryogenian Ice Age came to pass. This period of glaciation is known as the time when animals (in the form of ocean sponges) first came into existence.
The Huronian Ice Age took place between 2.4 and 2.1 billion years ago, making it the oldest and longest known period of glaciation on record. This glaciation event occurred during the Paleoproterozoic Era, between the periods known as Siderian and Rhyacian. Researchers have determined that this ice age was caused by the overproduction of cyanobacteria, which evolved the ability to photosynthesize in an environment that was largely made up of methane gas. The bi-product of their photosynthesis was oxygen, which slowly began to accumulate in the atmosphere. This overabundance of oxygen in the air led to the first major mass extinction known, during which all of the anaerobic organisms were killed. In addition, the large amount of oxygen resulted in an extreme decrease in the temperatures on earth. The Huronian Ice Age was first mentioned in the American Journal of Science in 1907.