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The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth.Dates in this article are consensus estimates based on scientific evidence, mainly fossils.
From amphibians came the first amniotes: Hylonomus, a primitive reptile, is the earliest amniote known. It was 20 cm (8 in) long (including the tail) and probably would have looked rather similar to modern lizards. It had small sharp teeth and probably ate small millipedes and insects. It is a precursor of later amniotes (including both the ...
During the Paleozoic, many modern groups of life came into existence. Life colonized the land, first plants, then animals. Two significant extinctions occurred. The continents formed at the break-up of Pannotia and Rodinia at the end of the Proterozoic slowly moved together again, forming the supercontinent Pangaea in the late Paleozoic. [148]
Human history is the record of humankind from prehistory to the present. Modern humans evolved in Africa around 300,000 years ago and initially lived as hunter-gatherers.They migrated out of Africa during the Last Ice Age and had spread across Earth's continental land except Antarctica by the end of the Ice Age 12,000 years ago.
Early micro-fossils may have come from a hot world of gases such as methane, ammonia, carbon dioxide, and hydrogen sulfide, toxic to much current life. [226] Analysis of the tree of life places thermophilic and hyperthermophilic bacteria and archaea closest to the root, suggesting that life may have evolved in a hot environment. [ 227 ]
The existence of this distant branch creates a much more complex picture of humankind during the Late Pleistocene than previously thought. [96] [99] Evidence has also been found that as much as 6% of the DNA of some modern Melanesians derive from Denisovans, indicating limited interbreeding in Southeast Asia. [100] [101]
The existential quantifier ∃ is often used in logic to express existence.. Existence is the state of having being or reality in contrast to nonexistence and nonbeing.Existence is often contrasted with essence: the essence of an entity is its essential features or qualities, which can be understood even if one does not know whether the entity exists.