History of the Earth - SpeedyLook encyclopedia

The history of the Earth roughly covers 4,6 billion years (4.567.000.000 years), since the formation of the Ground starting from the solar Nébuleuse until our days. This article presents a broad outline, summarizing the dominant scientific theories. Because of the difficulty that revêt the representation of broad periods of time, the analogy with one period of 24 hour S will be used, starting there are 4,567 exactly billion years, with the formation of the Earth, and being finished now. Each second of this period represents roughly: 53 000 years (or 53 Thousand-year-old S). The Big Bang and the origin of the Univers, of which the appearance is estimated there are 13,7 billion years, are located practically three Jour S before the release of our stop watch.

Origin

A theory indicates that the Earth was formed during the birth of the Solar system: what became the solar system thereafter was then a broad cloud in rotation, consisted of Poussière, of Roche and of Gaz. It was composed of Hydrogène and of Hélium produces by the Big Bang, as well as chemical elements heavier expelled by Supernova S. Then, as a theory suggests it, there are approximately 4,6 billion years a star near was destroyed in a Supernova and the explosion sent a Shock wave through the solar Nébuleuse, saving to him a Angular momentum. As the cloud accelerated its Rotation, the revolved and the Inertie flattened it in a Disque protoplanétaire directed perpendicularly compared to its axis of rotation.

The essence of the mass concentrated in the center and started to warm up, but small disturbances due to the collisions and the angular momentum of other broad remains created the conditions so that Protoplanète S start to be formed. Fallen from materials, the increase number of revolutions and compression related to gravity created an enormous quantity of kinetic energy in the center. The incapacity to transfer this energy sufficiently quickly outside caused a progressive rise of the temperature in the center of the disc. Finally, the nuclear Fusion of the Hydrogène with the Hélium started, and after contraction, a star T Tauri became our young person Sun. During this time, whereas gravity pushed the Matière to be condensed around the objects previously disturbed, the particles of dust and the remainder of the Disque protoplanétaire started to separate out of rings. Increasingly large fragments entered in collision the ones with the others and became larger objects, ultimement intended to become protoplanètes. Those included a grouping located roughly at 150 million Kilomètre S of the center: the Ground. The Solar wind of the news star T Tauri cleaned most of the material of the disc which had not already condensed in larger body.

The moon

See also: the Moon

The origin of the the Moon is always dubious, although many indices accredit the thesis of the great collision. The Earth could not have been the only planet being formed to 150 million kilometers of the Sun. An assumption indicates that another cluster would have been formed to 150 million kilometers of the Sun and the Earth, with their fourth or fifth Point of Lagrange. This planet, named Théia, would have been smaller than the current Earth, probably about of the size and the mass of Mars. Its orbit could have been stable initially, but have been destabilized as the Earth increased its mass by the accumulation of material.

Théia oscillated compared to the Earth until roughly 4,533 billion years (roughly 0:10 on our watch) date on which it entered in collision according to an angle obliques weak. The angle and speed were not sufficient to destroy, but a broad portion of its crust was ejected. Heavier elements of Théia were inserted in the middle of the Earth, while the materials and remaining ejections condensed in only one body in a few weeks. Under the influence of its own gravity, it became a more spherical body: the Moon. It is as theorized as the impact changed the axis of the Earth to produce broad the Inclinaison of the axis of 23,5° which is responsible for the seasons on the Earth - the ideal model of the origin of planets considers that they would have slopes of axis of 0° without recognizable season. The impact could have also accelerated the rotation of the Earth and initiate the Plate tectonics of planet.

The éon Hadéen

See also: Hadéen

The young Earth, during the éon Hadéen, was very different from the world such as we know it today. There were ocean and no oxygen in the atmosphere. It was bombarded by planetoids and materials resulting from the formation of the solar system. This bombardment, compound with the heat of the nuclear reactions, the after-heat and that due to the pressure of contraction, placed whole planet in a state of fusion. The heaviest elements were inserted in the center while lightest went up on the surface, producing the various envelopes of the Earth (see “internal Structure of the Earth”). The atmosphere of the Earth at its beginnings would have been composed of surrounding materials of solar nebula, particularly of light gas such as the Hydrogène and the Hélium, but the Solar wind and the heat of the Earth would have dispersed this atmosphere.

This changed when the Earth roughly reached 40% of its current ray, the gravitational forces authorizing the retention of an atmosphere which included water. The temperatures crumbled and the earth's crust accumulated on a solid surface. Zones began again to melt at the time of broad impacts, which intervened with intervals of a few tens or hundreds of years, and would be at the origin of partial differentiations.

Surface cools quickly, forming the solid Earth's crust in 150 million years; however new research suggests that the duration was rather of 100 million years, being given the level of Hafnium found to Jack hills in Australia. From 4 to 3.8 billion years before our era, the Earth knew one period of late meteoritic Bombardement. Vapor escaped from the crust and of gases were emitted by the volcanos, forming the terrestrial atmosphere. Additional water was brought by collisions of Bolide S, probably resulting from asteroids coming from the belt of asteroids most distant under the influence from the Jupiter gravity. The planet cools. The clouds were formed. The rain formed the Océan S in 750 million years (there are 3,8 billion years). Recent indices suggest that the oceans started to be formed there is 4,2 billion years. The new atmosphere probably contained Ammoniac, Méthane, Steam, Carbon dioxide and Azote, as well as moreover minor amounts of other gases. Any free oxygen would have been bound by hydrogen or minerals to surface. The volcanic activity was intense and, without Couche of ozone to prevent its entry, the ultraviolet radiation flooded surface.

Beginnings of the life

The first cell

Photosynthesis and oxygen

Endosymbiose and three fields of the life

Pluricellularity

Colonization of the ground

Humanity

Civilization

Recent events

See too

the Big Bang and its chronology
the geological time scale
the evolution of the forms of life
the Chronology of the evolution
the Natural history
the History of the world
the Créationnisme

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