istoria pământului în limba engleza
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The history of the Earth refers to the development of the planet Earth from its formation to the present. Almost all branches of natural science have contributed to the understanding of the main events of the Earth's past, characterized by constant geological changes and biological evolution.
The geological time scale, as defined by the international convention, presents the great periods of time from the beginning of the Earth to the present, and its divisions describe some decisive events in the history of the Earth. (Graph: Ga means "billion years ago"; Ma, "millions of years ago".) The Earth formed about 4.54 billion years ago, by accretion from the solar nebula, with about a third of the age of the Universe. Volcanic activity probably created the primordial atmosphere and then the ocean, but the early atmosphere contained almost no oxygen. Much of the Earth was melted due to frequent collisions with other bodies that led to extreme volcanism. During the early Earth stage, it is believed that there was a huge collision with a planet called Theia, a collision that formed the Moon. Over time, the Earth cooled, causing a solid crust to form and allowing liquid water to surface.
The Hadean eon represents the time before the reliable (fossil) record of life; it began with the formation of the planet and ended 4 billion years ago. The next Archean and Proterozoic eons produced the beginning of life on Earth and its earliest evolution. The following aeon is the Phanerozoic, divided into three eras: Paleozoic, an epoch of arthropods, fish and the appearance of life on land; Mesozoic, which included the rise, reign and climatic disappearance of non-avian dinosaurs; and the Cenozoic, which saw the rise of mammals. Humans appeared no more than 2 million years ago, a very short period on a geological scale.
The oldest undisputed evidence of life on Earth dates back at least 3.5 billion years, to Eoarchean times. There are microbial-covered fossils, such as stromatolites, 3.48 billion years old, discovered in Western Australia.
Other early physical evidence of a biogenic substance is: graphite on 3.7 billion-year-old metasedimentary rocks discovered in southwest Greenland and "biotic life remains" found in 4.1-billion-year-old rocks. in Western Australia. According to one researcher, "if life appeared relatively quickly on Earth ... then it could be common in the universe."
Photosynthetic organisms appeared 3.2-2.4 billion years ago and began to enrich the atmosphere with oxygen. Life remained largely rare and microscopic until about 580 million years ago, when complex multicellular life emerged, developed over time, and culminated in the Cambrian Explosion about 541 million years ago. This sudden diversification of life forms produced most of the major clusters known today and divided the Proterozoic eon from the Cambrian period of the Paleozoic era. It is estimated that 99% of the species that have ever lived on Earth, over five billion, have become extinct. Estimates of the current number of species on Earth range from 10 million to 14 million, of which about 1.2 million are documented, but over 86% have not been described. Recently, it has been claimed that 1 trillion species currently live on Earth, of which only 0.001% have been identified.
The Earth's crust has changed constantly since its formation, as has life since its first appearance. The species continues to evolve, taking on new forms, dividing into daughter species or disappearing in the face of the ever-changing environment. The process of plate tectonics continues to shape the continents and oceans of the Earth and the life it shelters. Human activity is now a dominant force affecting global change, affecting the biosphere, the Earth's surface, the hydrosphere and the atmosphere with the loss of wild land, overexploitation of the oceans, production of greenhouse gases, ozone depletion and soil degradation in general, air and water quality.
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