If humanity has always had the image of a blue and hospitable Earth, it turns out that this was not always the case. Before plants and animals began to populate it, our planet experienced periods cold enough to see its surface entirely covered in ice.
How did the Earth, located in the habitable zone of its star and on which water remains in a liquid state, transform into a ball of ice? And above all, how did she manage to get out of it and become capable of developing life again?
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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 radiative balance. It is the difference between the energy received from the Sun and that reflected by the continents, oceans and atmosphere.
From the beginning, carbon dioxide and methane acted as a heat shield. These two powerful greenhouse gases are responsible for regulating surface temperatures. Oxygen, methane and carbon dioxide are the main forces causing variations in Earth's climate.
In its early days, the Earth's atmosphere was composed mainly of carbon dioxide. Its concentration is gradually reduced by erosion linked to the appearance of the first continents. Initially, this decrease was compensated by the methane produced by methanogenic bacteria. But little by little, oxygen-producing bacteria appear. As methanogenic bacteria disappear, the concentration of methane in the Earth's atmosphere decreases sharply.
Climate is the result of a balance between the emission of greenhouse gases and their extraction from the atmosphere. Today, for Earth, the most important natural source of carbon dioxide is volcanism. The 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.
However, more than 3 billion years ago, when volcanism was already very active, continental surfaces, and consequently erosion, were minimal, leading to high levels of CO2 in the atmosphere.
How did the very first ice age occur on Earth 2.4 billion years ago? And what are the causes and consequences for the Earth of each glaciation? Before answering these questions, let's look at how an ice age is defined.
An ice age is defined as an episode of glaciation that occurred during a past geological period. Declining average temperatures are causing ice caps to expand across the planet. This phenomenon can last for millions of years. Throughout its history, Earth has experienced at least five major ice ages.
It is now scientifically proven that the Earth is going through cycles of climate change. The causes of these changes are diverse: modification of the Earth's orbit, changes in solar production, geological factors, etc. As a result, temperatures drop considerably over long periods. This is called an ice age. During an ice age, seafloor temperatures drop dramatically, allowing large glaciers, comparable in size to continents, to develop over much of the planet's surface.
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Today's program:
– 00:00 – Presentation
– 04:37 – Ice Ages
– 07:24 – Evidence of ice ages
– 11:52 – Causes of climate change
– 1:25 p.m. – Huronian Ice Age
– 31:24 – Cryogenian or Varanger Ice Age
– 40:38 – Andean-Saharan glaciation
– 56:22 – The Karoo Ice Age
– 01:02:10 – The Pliocene-Quaternary ice age
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