The Bacterium that will kill the Earth "the Man" (eBook)
206 Seiten
Books on Demand (Verlag)
978-2-322-53112-7 (ISBN)
Georges Ballin born on January 15, 1953, in a small village in the beautiful and green department of Aisne in France. Purely self-taught, decided at the age of 71 to take up writing. He embarks on the resumption of Memory and Worship Books in order to share them with the whole world.
Chapter / 1
Formation of the Solar System
The formation and evolution of the Solar System, the planetary system that houses the Earth, is determined by a model now widely accepted and known as the «solar nebula hypothesis». This model was developed in the eighteenth century by Emanuel Swedenborg, Emmanuel Kant and Pierre-Simon de Laplace. Developments following this hypothesis have involved a wide variety of scientific disciplines including astronomy, physics, geology and planetology. Since the beginning of the conquest of space in the 1950s and following the discovery of exoplanets in the 1990s, models have been questioned and refined to take into account new observations. According to estimates from this model, the solar system began to exist 4.55 to 4.56 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the mass of the initial cloud collapsed in the center of this area, forming the Sun, while its scattered remains formed the protoplanetary disc on the basis of which the planets formed, moons, asteroids and other small bodies of the Solar System.
The Solar System has evolved considerably since its initial formation. Many moons were formed from the gaseous disc and dust surrounding their associated planets, while it is assumed that others were formed independently and then captured by a planet. Finally, others, like the Earth’s natural satellite, the Moon, would (most likely) be the result of cataclysmic collisions. Collisions between bodies have occurred continuously to the present day and have played a central role in the evolution of the Solar System. The positions of the planets have slipped noticeably, and some planets have exchanged their places. It is planetary nebulae, and will leave behind a stellar corpse: a white dwarf. In the distant future, the gravitational attraction of stars passing in the neighborhood will then gradually tear the procession of planets of the old system away from its star. Some planets will be destroyed while others will be ejected into space. After several thousand billion years, it is likely that the Sun, having become a black dwarf, will be alone and frozen, without any gravitating body in its orbit.
The history of the current theory
Pierre-Simon de Laplace, one of the founders of the solar nebula hypothesis. The ideas relating to the origins and the future of the world are reported in the oldest known writings. Nevertheless, as the existence of the Solar System as it is currently defined was not yet known, the formation and evolution of the world did not refer to it. The first step that opened the door to a rational explanation was the acceptance of heliocentrism, which placed the Sun at the center of the system and the Earth in orbit around it. If this conception was known to the precursors, such as Aristarchus of Samos as early as 280 BC. J.-C., it remained in gestation for centuries, and it was widely accepted only at the end of the seventeenth century. The term "Solar System", strictly speaking, was first used in 1704. Immanuel Kant in 1755 and, independently, Pierre-Simon de Laplace in the eighteenth century were the first to formulate the hypothesis of the solar nebula. This hypothesis is the embryo of the standard theory currently associated with the formation of the Solar System. The most important criticism of this hypothesis was its apparent inability to explain the relative lack of angular momentum of the Sun compared to the planets. However, since the early 1980s, the observation and study of young stars have shown that they are surrounded by cold disks of dust and gas, exactly as predicted by the solar nebula hypothesis, which earned him renewed credit. Determining what the future evolution of the Sun, the main actor in the Solar System, will be, requires understanding where it gets its energy from. Arthur Eddington's validation of Albert Einstein's principle of relativity teaches us that the Sun's energy comes from the nuclear fusion reactions taking place at its heart. In 1935, Eddington continued this reasoning and suggested that other elements could also have formed within the stars. Fred Hoyle elaborates on these bases and explains that evolved stars which are called red giants create a large number of elements heavier than hydrogen and helium within them. When a red giant finally ejects its outer layers, the elements that it has accumulated there are released and can be reintegrated into the formation of new star systems.
The current model of the formation of the planets of the Solar System, by accretion of planetesimals, was developed in the 1960s by the Russian astrophysicist Viktor Safronov.
Dating
Using radioactive dating, scientists estimate the age of the Solar System to be about 4.6 billion years old. Terrestrial zircon grains included in rocks newer than them have been dated to more than 4.2 billion years ago, or even up to 4.4. The oldest terrestrial rocks have an age of about 4 billion years. Rocks of this age are rare, because the Earth's crust is constantly being shaped by erosion, volcanism and plate tectonics. To estimate the age of the Solar System, scientists need to use meteorites that formed at the beginning of the condensation of the solar nebula. The oldest meteorites, such as the Diablo Canyon meteorite, are 4.6 billion years old; therefore, the Solar System must at least be that age. The condensation of the Solar System from the primitive nebula would have occurred in 10 million years at most.
Training
Pre-solar-Nebula
According to the hypothesis of the presolar nebula, the Solar System was formed as a result of the gravitational collapse of a fragment of a molecular cloud several light-years in diameter. Even a few decades ago, it was commonly believed that the Sun formed in a relatively isolated environment, but the study of ancient meteorites revealed traces of isotopes with a reduced half-life, such as iron 60, which is formed only during the explosion of massive short-lived stars. This reveals that one or more supernovas occurred in the vicinity of the Sun while it was forming. A shock wave resulting from a supernova could have triggered the formation of the Sun by creating denser regions within the cloud, to the point of initiating its collapse. Because only short-lived massive stars form supernovae, the Sun would have appeared in a wide region of massive star production, probably comparable to the Orion nebula. The study of the structure of the Kuiper Belt and the unexpected materials found there suggests that the Sun was formed among a set of stars grouped in a diameter of 6.5 to 19.5 light-years and representing a collective mass equivalent to 3,000 times that of the Sun. Different simulations of a young Sun, interacting with nearby stars during the first 100 million years of its life, produce abnormal orbits. Such orbits are observed in the outer Solar System, especially those of scattered objects. One of these collapsing regions of gas, the "pre-solar nebula", would have formed what would become the Solar System. This region had a diameter between 7,000 and 20,000 astronomical units and a mass just greater than that of the Sun. Its composition was approximately the same as that of the current Sun. It included hydrogen, accompanied by helium and traces of lithium produced by primordial nucleosynthesis, forming about 98% of its mass. The remaining 2% of the mass represent the heavier elements, created by nucleosynthesis of older generations of stars. At the end of their lives, these ancient stars had expelled the heavier elements in the interstellar medium and in the solar nebula.
Because of the conservation of angular momentum, the nebula rotated faster as it collapsed. As the materials within the nebula condensed, the frequency of collisions of the atoms that composed them increased, converting their kinetic energy into heat. The center, where most of the mass was collected, became hotter and hotter, much more than the disk surrounding it. Over a period of 100,000 years, the competing forces of gravity, gas pressure, magnetic fields and rotation caused the contraction and flattening of the nebula into a rotating protoplanetary disk with a diameter of about 200 au and forming at its center a hot and dense protostar (a star within which hydrogen fusion cannot yet begin). At this point in its evolution, the Sun was probably a variable star of the T Tauri type. Studies of T Tauri stars show that they are often accompanied by disks of pre-planetary matter with masses of 0.001 to 0.1 solar mass. These disks extend over several hundred astronomical units — the Hubble Space Telescope has observed protoplanetary disks up to 1,000 au in diameter in star-forming regions such as the Orion nebula— and reach a temperature of a thousand kelvins at most.
After 50 million years, the temperature and pressure in the heart of the Sun became so high that its hydrogen began to merge, creating an internal energy source that opposed gravitational contraction until hydrostatic equilibrium was achieved. This marked the entry of the Sun into the first phase of its life, known as the main sequence. Main sequence stars get their energy from the fusion of Hydrogen into helium in their core. The Sun remains a main sequence star to this day.
Formation of planets
It is assumed that the various planets were formed on the basis of the solar nebula, a disc-shaped cloud, made of gas and dust, not having been directly engulfed in the formation of the Sun. The phenomenon, currently retained by the scientific community, according to...
Erscheint lt. Verlag | 16.5.2024 |
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Sprache | englisch |
Themenwelt | Naturwissenschaften ► Geowissenschaften ► Mineralogie / Paläontologie |
Sozialwissenschaften ► Politik / Verwaltung | |
Technik | |
Schlagworte | evolution of bacteria • history of the climate • Pangea • science and life of the earth • the ancestors of the human species |
ISBN-10 | 2-322-53112-X / 232253112X |
ISBN-13 | 978-2-322-53112-7 / 9782322531127 |
Informationen gemäß Produktsicherheitsverordnung (GPSR) | |
Haben Sie eine Frage zum Produkt? |
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