Earth History.
The history of Earth covers approximately 4.6 billion years (4,567,000,000 years), since the formation of the Earth from the solar nebula to date.
Summary |
Origin
The age of the universe is estimated to be approximately 13.7 billion years . These include a group at approximately 150 million kilometers from the center: the Earth. The solar wind of the new T Tauri star cleans up the largest portion of gas and dust disk, which had not already condensed into larger bodies.
The Moon
The origin of the Moon is still uncertain, although many indices supports the theory of the big crash. Earth could not have been the only planet to have formed at 150 million km from the Sun. One hypothesis indicates that another cluster will be formed at 150 million km from the Sun and Earth, in their fourth or fifth Lagrangian point. This planet named Theia , would have been smaller than the present Earth, probably about the size and mass of Mars. Its orbit could be stable at first, but have progressively destabilized as the Earth increased its mass by the accumulation of material.
Theia oscillates relative to the Earth to approximately 4.533 billion years , when it collided at an oblique angle low. The angle and speed are not sufficient to destroy the Earth, but a large portion of the crust is ejected. Heavier elements of Theia sinking at the heart of the Earth, while the remaining materials and ejections are condensed into one body in a few weeks. Under the influence of its own gravity, it becomes more spherical body: the Moon . At that time, the Moon orbit more slowly and at a distance 15 times less than today . It also advances the theory that the impact would have changed the Earth's axis to produce the large axial tilt of 23.5 which is responsible for the seasons on Earth - the ideal model of the origin of planets considered they have inclinations of 0 axis, so no recognizable season. The impact could also have accelerated the rotation of the Earth by giving it a turnaround time of six hours , and initiated the tectonic plates of the planet.
The Hadean Eon
The young Earth during the aeon Hadean , was very different from the world as we know it today. There was no ocean and no oxygen in the atmosphere. It was bombed by planetoids and materials from the formation of the solar system. This bombing, combined with the heat of radioactive transformations, residual heat and that due to the pressure of contraction, putting the entire planet in the molten state. The heavier elements sink to the center while the lighter rise to the surface, forming the various envelopes of the Earth (see " Structure of the Earth ") and thus producing additional heat.
The atmosphere of the Earth in its infancy was composed of material surrounding the solar nebula, particularly in light gases such as the hydrogen and helium , but the solar wind and the heat of the Earth would have dispersed this atmosphere. A new atmosphere is created from magma degassing. These gases from terrestrial rocks were molten mainly of nitrogen , of carbon dioxide , the ammonia of methane , the water vapor and smaller amounts of other gases.
The earth cools and the crust is formed around bacteria on the surface. Enter new areas of molten during large impacts, which occur at intervals of a few tens or hundreds of years and are the cause of partial differentiation . 4 to 3.8 billion years before our era, the Earth experienced a period of Late Heavy Bombardment , as the Moon and other solar system bodies. This phase is probably due to rearrangement of the outer solar system.
The planet continues to cool, and rain lead to the formation of the oceans there are 4.2 billion years , .
Early life
The origins of life , which are thought to date from about 3.5 to 3.8 billion years, remain uncertain. There are three main hypotheses explaining the origin of the first molecules Organic
- Condensation on mineral surfaces.
- Hydrothermal vents on the ocean floor.
- The primitive extraterrestrial origin, called "exogenesis" (which only pushes the origin but also does not explain the mechanisms).
In the first 2 cases, the Earth is so favorable prebiotic conditions (probably water , ammonia , methane and hydrogen ...) the creation of simple organic molecules ( urea , formaldehyde , hydrogen cyanide , amino acids ...). These building blocks of life are changing protocells then isolated from membranes and whose RNA (ribonucleic acid) is capable of replication. The DNA then replaces the RNA in the supporting role of the genome and that the onset of the current organization of the living.
The most commonly accepted hypothesis is that life may have formed in hot springs. These hot springs were first stripped of water, but clay, because the organics are very easily soluble in water. However, the concentration of amino acids is low. To increase the likelihood that life is likely to emerge, it is possible that life may have formed in porous rocks, in hot springs. So, these rocks form a sort of bottleneck, where the amino acids and other molecules would be compiled. Thus, the concentration increases, the collisions between the molecules as well, and the likelihood of complex organic structures are also increasing.
The first cell
The exact dates of onset of the first cell is not known by scientists. The oldest known fossil of cells are stromatolites dating from 3.5 billion years.
Scientists have found fossils of micro organisms in rocks from Isua in Greenland dated at 3.8 billion years. But it is not certain that it is not artifacts.
Other paleontological traces of life were found:
- Warrawoona microfossils (Australia) dated 3.5 Ga
- of Microfossils Onverwacht and Fig Tree (South Africa) dated to 3.4 to 3.5 Ga
- microfossils in Bulawayo (Zimbabwe) dated 2.8 Ga
- Gunflint microfossils (Ontario) dated 2 Ga
- Bitter Springs microfossils (Australia) dated from 850 Ma
Photosynthesis and oxygen
Endosymbiosis and the three domains of life
multicellularity
Colonization of the land
Humanity
The Homo sapiens appears in modern Africa there are approximately 200 000 years.
Civilization
Recent Events
See also
- The Big Bang and its chronology
- The geologic time scale
- The evolution of life forms
- The chronology of developments
- The natural history
- The history of the world
Notes
- New Image of Infant Universe Reveals Era of First Stars, Age of Cosmos, and More , NASA, February 11, 2003
- Eric J. Chaisson, Solar System Modeling , Tufts University, 2005
- Carsten Munk, Jrg A. Pfnder, Stefan Weyer, Anette Bchl, Thorsten Kleine, Klaus Mezger, Evolution of Planetary Cores and the Earth-Moon System from Nb / Ta Systematics , Science (volume 301, No. 5629, pp 84-87), July 4, 2003
- G. Jeffrey Taylor, Origin of the Earth and Moon , NASA, April 26, 2004
- a and b VNR Super-science 2 - "The Moon and its mysteries" dated 2005.
- Hannes Alfven, Gustaf Arrhenius, Evolution of the Solar System , National Aeronautics and Space Administration, 1976
- Robert Roy Britt, Evidence for Ancient Bombardment of Earth , Space.com, July 24, 2002.
- Cavos AJ, JW Valley, SA Wilde, EIMF, Magmatic 18 O in 4400-3900 Ma detrital zircons: A Record of the alteration and recycling of crust in the Early Archean , Earth and Planetary Science Letters (volume 235, issue 3 -4, pp. 663-681), July 15, 2005)
- Edward Young, Executive Summary 2005 , July 4, 2005.
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