Mysteries of the Earth’s formation
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Mysteries of the Earth’s formation

Mysteries of the Earth’s formation
Planets are born when stars form. Our planet, Earth, formed at the same time as the Sun. Before the Sun came into being, a huge cloud of gas and dust (the pre-solar nebula) occupied the area where the solar system would be born.

Mysteries of the Earth’s formation
Planets are born when stars form. Our planet, Earth, formed at the same time as the Sun. Before the Sun came into being, a huge cloud of gas and dust (the pre-solar nebula) occupied the area where the solar system would be born. About 4.6 billion years ago, this cloud began to contract in on itself under the effect of its own mass; the contraction was perhaps itself triggered by the explosion of a neighbouring star (a supernova).

This gravitational collapse took a long time, about 100 million years. It started very slowly and gradually increased in speed and violence as particles of dust and gas aggregated to form larger and larger masses. Over time, the matter at the centre of this collapse became increasingly dense, massive and hot (the future star). Around the centre spun a disk of matter called the protoplanetary disc that would eventually give rise to the planets.

By 4.54 billion years ago, the proto-Earth had formed and was being constantly bombarded by a rain of meteorites large and small. Then, a few million years later, 4.53 billion years ago, an event of extreme violence and importance occurred: the cataclysmic encounter of Earth with Theia, a sister planet about the size of Mars currently. This tremendous collision led to the fusion of the two planets and created a ring of debris that would eventually form the Moon.

Since then, the Moon has been Earth’s companion and causes, in particular, the phenomenon of the tides. Some researchers believe that the tides—which were much more frequent 4 billion years ago because the Earth turned on its axis every 12 hours instead of every 24, and much higher because the Moon was twice as close to the Earth as it is today—may have contributed to the emergence of life on Earth by helping the formation of the nucleic acids that are central to the development of genetic information contained in cell nuclei.
Between 4.1 and 3.9 billion years ago, the Earth went through another period of intense meteoritic bombardment (the late heavy bombardment), which may have been triggered by the migration of the gas giants to their current orbits. During these several hundred million years, the Earth, Moon, Mars, Venus, and Mercury were riddled with craters and on several occasions, Earth suffered impacts so monumental they would have evaporated the oceans and melted the planet’s crust. If life appeared before this tumultuous period, it would certainly have been wiped out by these meteor strikes. However, some scientists believe that bacteria could have survived a number of kilometres below the Earth’s surface.

And hence, it is 3.8 billion years ago that the first traces of an important event in the history of the Earth (and perhaps the universe?) become visible, and the first forms of living matter were born out of non-living matter. While there are still some murky areas about this transition, scientific understanding of the origins of life has progressed rapidly over the past 60 years. In 1952, biochemists Stanley Miller and Harold Urey conducted one of the most famous experiments of the 20th century. They showed that simple chemical compounds (amino acids, nucleic acids, sugars, lipids, etc. ), which are needed for the development of the complex molecules that make up living cells, could form relatively easily on the primitive Earth. In the lab, they reproduced the “recipe” of prevailing conditions on Earth 3.8 billion years ago—i.e., water, methane, ammonia, and hydrogen, along with heat and simulated lightning—which created 20 amino acids and other organic compounds.

Since the 1970s, very strange life forms have been discovered in different sites around the world with extreme conditions, whether they be very hot, very cold, very salty, very acidic, very alkaline, very dry, very high pressure, or very isolated. These life forms are called extremophiles. Not only to they tell us about what life might be like elsewhere in the universe, they also tell us about what the first living things on Earth may have been like.

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