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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 earliest evidence for life on Earth includes: 3.8 billion-year-old biogenic hematite in a banded iron formation of the Nuvvuagittuq Greenstone Belt in Canada; [30] graphite in 3.7 billion-year-old metasedimentary rocks in western Greenland; [31] and microbial mat fossils in 3.48 billion-year-old sandstone in Western Australia.
Rare Earth was succeeded in 2003 by the follow-on book The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of our World, also by Ward and Brownlee, which talks about the Earth's long-term future and eventual demise under a warming and expanding Sun, showing readers the concept that planets like Earth ...
In the 2008 lecture series through The Teaching Company's Great Courses entitled Big History: The Big Bang, Life on Earth, and the Rise of Humanity, Christian explains Big History in terms of eight thresholds of increasing complexity: [51] The Big Bang and the creation of the Universe about 14 billion years ago [51]
The definition of life has long been a challenge for scientists and philosophers. [2] [3] [4] This is partially because life is a process, not a substance. [5] [6] [7] This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth.
It took 4.5 billion years before humanity appeared on Earth, and life as we know it will see suitable conditions for 1 [94] to 2.3 [95] billion years more. Red dwarfs, by contrast, could live for trillions of years because their nuclear reactions are far slower than those of larger stars, meaning that life would have longer to evolve and survive.
The ozone layer protects the planet from the harmful radiations from the Sun, and free oxygen is abundant enough for the breathing needs of terrestrial life. [24] Earth's magnetosphere, generated by its active core, is also important for the long-term habitability of Earth, as it prevents the solar winds from stripping the atmosphere out of the ...
A life form (also spelled life-form or lifeform) is an entity that is living, [1] [2] such as plants , animals , and fungi . It is estimated that more than 99% of all species that ever existed on Earth, amounting to over five billion species, [3] are extinct. [4] [5] Earth is the only celestial body known to harbor life forms. No form of ...