What are the major ice ages in Earth’s history?

The harsh climate experienced in Europe during the Ice Age spurred the evolution of Neanderthal physical characteristics.

The Earth has experienced at least five major ice ages in its 4.57 billion years of history: the Huronian glaciation (2.4 to 2.1 billion years ago), the Sturtian/Marinoan glaciation (710 to 640 mya), the Andean-Saharan glaciation (460 to 430 mya), the Karoo Ice Age (350 to 260 mya), and the more recent Ice Age, which is ongoing (40 to 0 mya). The definition of an Ice Age is a long-term drop in global temperatures from historical norm, accompanied by an extension of continental ice sheets. Each Ice Age is cyclical, usually on timescales of 44,000 and 110,000 years, during which glacial ice rhythmically extends and retreats.

The Earth has gone through at least five major ice ages.

The precise causes of historical Ice Ages are unknown, but likely arose due to a variety of factors, including: positions of continents, atmospheric composition (greenhouse gases), volcanic activity, the Earth’s albedo (reflectivity), variations in distance from the Sun (Milankovitch cycles), variations in solar production and asteroid impacts. When the right variables are present, an Ice Age begins, and once it starts, the positive feedback effects kick in. The strongest is simply that ice is more reflective than land or forest, so large areas covered by ice sheets reflect the Sun’s rays, causing further drops in temperature and an increase in glaciation.

The ice covering Greenland indicates that the world is in the midst of an Ice Age.

For the most part, the Earth is not in an Ice Age, and the average global temperature is around 22 °C (71 °F). Ice sheets are almost completely absent, found only at high altitudes (alpine glaciers). The poles are cold but not covered in ice, and the forests stretch from pole to pole. Dinosaur fossils have been found less than 10° latitude from the ancient South Pole. Only for about 15% of Earth’s history has there been an Ice Age.

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Antarctica wasn’t always covered in ice.

The two most famous Ice Ages are probably the Sturtian/Marinoan glaciation and the more recent Ice Age. The Sturtian/Marinoan glaciation was so severe that evidence of continental glaciers around the equator was found in this period. The global average temperature may have dropped below -30 °C (-22 °F), colder than present-day Antarctica. Some scientists even believe that the oceans froze from top to bottom during this period, resulting in an “Earth in a snowball” scenario. Life would have survived in refuges such as deep-sea hydrothermal vents.

Human fossils from before the last glacial period are only found in small parts of Europe, such as Spain and southern France.

The most recent Ice Age is well known because we humans had our entire history in it. We think the ice sheets covering Greenland and Antarctica are typical, although they are not. More than about 10,000 years ago, there was a severe glacial period that covered continents in glaciers as far south as Chicago and Paris. During this time period, humans mostly had to avoid colonizing Europe or northern Asia, as these areas were completely frozen over. For this reason, human fossils from before the last glacial period are found only in Africa, the Middle East, China, Southeast Asia, Australia, and only in small parts of Europe, such as Spain and southern France.

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