The Earth | 01 - What is the History of our Planet?

Marked by mass extinctions, catastrophic episodes but also periods of stability, the Earth never stops evolving. Mysterious blue planet of the universe, it is the only one known today to shelter a human life form.

Here is a look back at its accretion and evolution. In order to represent more easily the time scale, the values of billions and millions of years are reduced to twelve hours, i.e. one turn of the dial.

The accretion of the Earth occurs at 00h00 and the year 2022 is represented by 12h00. During these twelve hours we will go through four chronological periods: the Hadean, the Archean, the Proterozoic and the Phanerozoic.

Earth History:

Now 4.54 billion years ago, the accretion of the Earth begins with the formation of the Sun.

A few million years earlier, the gravitational collapse of a tiny part of a molecular cloud made our star appear. A disk of gas and dust forms around the young celestial body.

These grains slowly clump together until they form small solid bodies, the first fruits of planets in the making, the planetesimals. Under the effect of gravity, these planetesimals reach up to a few kilometers in diameter, eventually forming embryos of planets while clearing the disk of its original dust.

The farther the orbits are from the Sun, the more massive they are since they find more material to agglomerate along their path.

After a certain distance from the Sun, the planets are able to attract the gases of clouds made of hydrogen and helium until they collapse on themselves giving birth to the gas giants that we know well: Jupiter and Saturn.

Uranus and Neptune being smaller, they do not keep the gases but only their core of rock and ice.

The planets that form closer to the Sun are called telluric, they are composed of rocks and metals. They are violently struck when their orbits cross to such an extent that only four remain: Mars, Venus, Mercury and Earth.

The formation of all these planets lasts 100 million years.

Theia:

Theia, a protoplanet, wanders in a stable zone of the cosmos, at the same distance from the Sun as the Earth.

As it reaches the size of Mars, Theia is destabilized by the gravitational influence of the other planets. Its orbit becomes chaotic and it violently collides with the young Earth in formation 4.52 billion years ago.

The shock is so violent that the iron core of Theia plunges into the heart of the Earth. The rest of the planet and part of the Earth's mantle are ejected into the cosmos.

All these materials in orbit around the Earth eventually gather and give birth to the satellite that is the Moon, some 22 500 kilometers.

The Moon stabilizes the Earth's axis of rotation and slows down this same movement by the phenomenon of tidal friction, which explains why at that time a day lasts only 6 hours and a year has 1,434 days.