Did you know that, in the past, the Earth experienced periods so cold that it became so icy that it resembled a "snowball"?
While mankind has always had an image of a blue, hospitable Earth, it turns out that this wasn't always the case. Before plants and animals began to populate it, our planet experienced periods cold enough to see its surface completely covered in ice.
How did the Earth, which lies in its star's habitable zone and on which water remains in a liquid state, turn into a ball of ice? And, above all, how did it manage to get out and become suitable again for the development of life?
The Ages of Planetary Glaciations
- Since the formation of the Earth, the atmosphere has played the role of a heating blanket. In its early years, the Sun released 30% less energy than it does today. Since then, every billion years, its power has increased by 7%. Despite this, the Earth was much warmer than it is today. This phenomenon is due to its radiation balance. This is the difference between the energy received from the Sun and that reflected by the continents, oceans and atmosphere.
From the very beginning, carbon dioxide and methane have acted as a heating shield. These two powerful greenhouse gases are responsible for regulating surface temperatures. Oxygen, methane and carbon dioxide are the main forces driving variations in the Earth's climate.
In its early days, the Earth's atmosphere was mainly composed of carbon dioxide. Its concentration is gradually reduced by the erosion associated with the appearance of the first continents. Initially, this decrease was offset by the methane produced by methanogenic bacteria. Gradually, however, oxygen-producing bacteria appear. As the methanogenic bacteria die out, the concentration of methane in the earth's atmosphere falls sharply.
Climate is the result of a balance between the emission of greenhouse gases and their extraction from the atmosphere. For the Earth today, the most important natural source of carbon dioxide is volcanism. Water runoff then reacts with continental rocks to remove CO2 from the atmosphere and fix it in the form of carbonate, which accumulates as sediment on the seabed.
Nevertheless, over 3 billion years ago, although volcanism was already very active, continental surfaces, and consequently erosion, were derisory, resulting in high levels of CO2 in the atmosphere.
How did the very first ice age on Earth occur 2.4 billion years ago? And what are the causes and consequences for the Earth of each glaciation? Before answering these questions, let's take a look at how an ice age is defined.
An ice age is defined as an episode of glaciation that took place during a past geological period. Falling average temperatures cause ice caps to expand across the planet. This phenomenon can last for millions of years. Throughout its history, the Earth has experienced at least 5 major ice ages.
It is now scientifically proven that the Earth goes through cycles of climate change. The causes of these changes are diverse: modification of the Earth's orbit, changes in solar output, geological factors... As a result, temperatures drop significantly over long periods. This is known as an ice age. During an ice age, seabed temperatures drop considerably, allowing large glaciers, comparable in size to continents, to develop over a large part of the planet's surface.
00:00:00 - Introduction
00:04:37 - Ice ages
00:07:24 - Evidence of ice ages
00:11:52 - Causes of climate change
00:13:25 - Huronian Ice Age
00:31:24 - Cryogenian or Varanger ice age
00:40:38 - Andes-Saharan glaciation
00:56:22 - Karoo Ice Age
01:02:10 - The Pliocene-Quaternary Ice Age