The Earth has had some seriously cold periods. Two major ice ages happened during the Neoproterozoic Era. These were the Sturtian and Marinoan ice ages. During these times, the planet was covered in ice from pole to pole. This is known as a "snowball Earth. " The ice ages lasted for millions of years. They were caused by a runaway ice-albedo feedback. This means that as ice covers more of the Earth, it reflects more sunlight back into space. This makes the planet even colder. This process can lead to a runaway effect, where the planet freezes over completely.

The duration of these ice ages is important. It affects how habitable the planet is. For example, animals first appeared on Earth between these two ice ages. Scientists have figured out that the Sturtian ice age lasted about 56 million years. The Marinoan ice age, however, is less clear. It lasted between 4 and 15 million years. This is a big range of uncertainty. New research has narrowed it down. The Marinoan ice age in Namibia lasted about 4 million years. During this time, the ice sheet did not move much vertically. This means it was very stable. This stability is consistent with a "hard snowball" state. This is a state where the ice is very thick and stable. It does not melt or advance much.

The difference in duration between the Sturtian and Marinoan ice ages is interesting. It suggests that there were different paths to deglaciation. The Sturtian ice age ended due to a slow buildup of carbon dioxide. This gas traps heat in the atmosphere. The Marinoan ice age, however, ended due to a sudden change in radiation. This could have been caused by a change in the Earth's orbit or a volcanic eruption. This sudden change caused the ice to melt quickly.

The short duration of the Marinoan ice age may have been important for life. It allowed animals to survive and evolve. This is an important lesson for understanding habitability on other planets. If a planet has a short ice age, it may be more likely to support life. This is because life has a better chance to survive and evolve. The study of these ice ages can help us understand the conditions that are necessary for life to exist.

Earth's Big Freeze: How It Ended and What It Means for Life

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