🌍 Life.
Life is a natural phenomenon known today exclusively on Earth.
Life is characterized by the ability to reproduce identically, the presence of water, a metabolism and an ability to maintain physicochemical parameters.
The Earth was formed 4.5 billion years ago. No form of life inhabits it in its primitive form. It does not look like the planet we know today. Covered by a thick, extremely hot atmosphere, the Earth has an orange hue. Its surface is totally unrecognizable. Everything is so quiet .... so empty.... so silent....


🔥 As a reminder, videos are published on SUNDAYS at 6:00 PM.


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💥 The Story of Life:
- Over time, the Earth cools. The water contained until then in its primitive atmosphere passes to the liquid state, the hydrosphere appears. It starts to rain. Water fills the depressions and the oceans are formed.
Life appeared on Earth 3.5 billion years ago, about 1 billion years after its formation. At the beginning in the form of simple unicellular organisms, they evolve in an aquatic environment and are small in size, about a few tenths of a millimeter. Little by little, the cells group together and move closer together. They absorb sunlight, water and gas. They develop and invade the sea bed. In several million years, the cells perfect themselves, and gather. They will form multi-cellular beings of various shapes and sizes, larger than the unicellular ones, a single nucleus not being able to control a too large quantity of cytoplasm. Multi-cellular organisms see their cells associate in tissues which will allow them to accomplish functions.

540 million years ago, a real explosion of diversity occurred, the Cambrian explosion. The ideal conditions are met for the evolution of many species of marine animals. The oceans were filled with living creatures similar to jellyfish, shrimp and worms. Some species kill each other and get bigger and bigger. From the abyss to the surface of the water, the aquatic world is teeming with life. Green seaweed grows in the shallow waters and will evolve to become the first plants to grow on land. Mosses cover the land areas.

Today, our planet has an extraordinary richness and diversity of animals and plants. And yet, the history of life is not a calm one. The latter has not been spared and it has undergone great upheavals having each time consequences on its evolution. Today, the forces of nature seem calmer and the Earth seems to have found its balance. And yet... A species is wiped out from the planet every 20 minutes. The equivalent of seven soccer fields are deforested every hour.
After the five great cataclysms that led to the five greatest mass extinctions, it would seem that the Earth is once again entering a brutal phase of upheaval in the climate and the composition of life. But let's go back to these periods of change that were decisive for the evolution of the fauna and flora as we know it today on our planet.

We are in the second of the six systems composing the Paleozoic, the Ordovician which lasts from - 488 million years to - 443 million years. This new period begins following the Cambrian extinction, probably due to an asteroid impact. At the beginning of this period, life existed only in the sea, a continental and shallow sea. The animal world was dominated by trilobites and brachiopods, which had a great evolutionary success in the Paleozoic. On land, it is nothingness, oxygen is rare, neither plants nor animals can develop. The supercontinent Gondwana includes all the continents of the southern hemisphere and is surrounded by the ocean Panthalassa in which all living species are swarming.
More than 490 million years ago, before the Ordovician, the atmosphere was strongly filled with CO2 which induced a greenhouse effect and consequently very high temperatures. The oceans reached up to 45 °C.


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🎬 On the program today:
- 00:00 - Introduction
- 04:54 - 445 million years ago: Ordovician extinction
- 17:45 - 360 to 375 million years ago: extinction of the Devonian
- 28:46 - 252 million years ago: Permian extinction
- 39:00 - 200 million years ago: Triassic extinction
- 53:05 - 66 million years ago: Cretaceous - Paleogene extinction
- 01:04:52 - 2023: Towards a sixth extinction?

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