The Hadean is the most distant time in the history of planet Earth, the one where the formation of the solar system "ends". The Hadean begins there are ≈4,54 billion years and lasts ≈700 million years.
The solar system was born of a huge cloud of gas and dust certainly caused by the explosion of a nearby supernova.
When starting the Hadean, the protosolar nodule has already collapsed and our Sun, which captured alone 99.86% of the mass of the nebula, shines with all its lights since ≈100 million years. The rest of the nebula (0.14%), made of the same materials as the Sun, forms a disk (see picture) that is pushed by the solar wind 100,000 times more powerful than today. Dust grains located in the same plane, have identical speed and without rebound easily agglutinate forming material grains, the size of a rock to the size of a protoplanet (size of the moon). This accretion phase will last 100,000 years.
Larger objects capture the smallest, by their gravitational force and thus begin to get a place around the Sun. But the sky is dark, it remains congested with rocks billion, more or less massive crashing on each other. A dense disk of small planetesimals of rock and ice, extends still further, to 35 AU Founded in 1958, it is the distance unit used to measure distances to objects in the solar system, this distance is equal to the distance from Earth to the sun. The value of the astronomical unit is exactly 149 597 870 700 m, at its General Assembly held in Beijing from 20 to 31 August 2012, the International Astronomical Union (IAU) adopted a new definition of the astronomical unit, unit of length used by astronomers around the world to express the dimensions of the solar system. One will retain about 150 million kilometers. A light year is approximately 63,242 AU. Mercury: 0.38 AU, Venus 0.72 AU, Earth: 1.00 AU, March: 1.52 AU, Asteroid Belt: 2 to 3.5 AU, Jupiter 5.21 AU, Saturn: 9 54 ua, Uranus: 19.18 ua, Neptune: 30.11 ua, Kuiper Belt: 30 to 55 AU, the Oort Cloud: 50 000 AU. from the Sun. The orbits are unstable, and objects are constantly deflected by the gravitational perturbations of the largest planetesimals and in this infernal ballet, all these bodies often cross and collide incessantly. This is the time of the Late Heavy Bombardment, called (LHB), it was at this time that the number of large objects decreases. There remains only about twenty bodies of a size between that of the Moon and Mars and the bodies turn now on nearly circular orbits.
The orbits are always crossed by fireballs and the number of very large objects will further decrease. Thus sets up the accretion phenomenon that will lead to the formation of the current planets.
Among the millions of small impacts, a cataclysmic impact will transform our young Earth.
One object, about the size of Mars (ten times less massive than the current Earth) will collide with the primitive Earth.
The infernal collision tear a portion of terrestrial mantle without touching the core and disperses the material in an orbit beyond the Roche limit The Roche limit and Roche radius is the distance at which a small celestial body will disintegrate because of tidal forces of another celestial body whose attraction force exceeds the self-attraction of the small body. In other words, the Roche limit is the minimum distance from the center of the planet, which allows the material to come together to form, for example, a sufficiently large moon..
The gigantic heat impact vaporizes its atmosphere and refractory materials retained by Earth's gravity will form the Moon.
Quickly in a few thousand years, a huge ball of rock covered with incandescent lava, succeed to get a place on a privileged orbit near the Sun. A young Earth will impose in this burning chaos and its history will begin, then we are at the beginning of the Hadean.
During the first million years, the Earth will cool quickly is during this cooling that forms a solid earth's crust (≈160 million years after its formation) and a new atmosphere resulting from degassing fluids inner layers.
nota : there are some rocks dating from the Hadean, the first moments of the Earth, especially in the east of Australia, in the Jack Hills an area known for it. Zircon extracted from a rocky outcrop in 2001 attests. The age of the zircon was estimated at 4.4 billion years, only 100 million years after the formation of the Moon, there are 4.5 billion years. The earth's crust was formed ≈160 million years after the formation of our planet there are 4.54 billion years.
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|Primitive Nebula||4.60 billion years|
|Sun||4.568 billion years|
|Earth||4.54 billion years|
|Moon||4.50 billion years|
|Earth's crust||4.40 billion years|
|Earth's atmosphere ||4.40 billion years|| || |
Image : an accretion disk forms around the rising star, the real picture is the most accurate, ever made, of a nebula proto stellar and therefore protoplanetary. This picture was taken in the millimeter wave, more accurate than the images usually obtained in the visible with the Space Telescope NASA / ESA Hubble. We clearly see the protoplanetary disk around the young star HL Tauri. These new observations ALMA reveal structures in the disk never seen before and even reveal the possible locations of training planets in dark areas at the heart of the emerging system. This image was taken with the network of 66 antennas of the giant radio (ALMA) located in the Atacama Desert in northern Chile. HL Tauri is 450 light years away in the constellation Taurus.
Credit : ALMA (ESO/NAOJ/NRAO).