Life

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Life is matter that has biological processes, such as signaling and the ability to sustain itself. It is defined descriptively by the capacity for homeostasis, organisation, metabolism, growth, adaptation, response to stimuli, and reproduction. All life eventually reaches a state of death, and none is immortal. Many philosophical definitions of living systems have been proposed, such as self-organizing systems. Defining life is further complicated by viruses, which replicate only in host cells, and the possibility of extraterrestrial life, which could be very different from life on Earth. Life exists all over the Earth in air, water, and soil, with many ecosystems forming the biosphere. Some of these are harsh environments occupied only by extremophiles. The life in a particular ecosystem is called its biota. Life has been studied since ancient times, with theories such as Empedocles's materialism asserting that it was composed of four eternal elements, and Aristotle's hylomorphism asserting that living things have souls and embody both form and matter. Life originated at least 3.5 billion years ago, resulting in a universal common ancestor. This evolved into all the species that exist now, by way of many extinct species, some of which have left traces as fossils. Attempts to classify living things, too, began with Aristotle. Modern classification began with Carl Linnaeus's system of binomial nomenclature in the 1740s. Living things are composed of biochemical molecules, formed mainly from a few core chemical elements. All living things contain two types of macromolecule, proteins and nucleic acids, the latter usually both DNA and RNA: these carry the information needed by each species, including the instructions to make each type of protein. The proteins, in turn, serve as the machinery which carries out the many chemical processes of life. The cell is the structural and functional unit of life. Smaller organisms, including prokaryotes (bacteria and archaea), consist of small single cells. Larger organisms, mainly eukaryotes, can consist of single cells or may be multicellular with more complex structure. Life is only known to exist on Earth but extraterrestrial life is thought probable. Artificial life is being simulated and explored by scientists and engineers.

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Article title : Life
"Life is matter that has biological processes, such as signaling and the ability to sustain itself. It is defined descriptively by the capacity for homeostasis..."
Article title : Life (disambiguation)
"Look up Life or life in Wiktionary, the free dictionary. Life is the characteristic that distinguishes organisms from inorganic substances and dead objects..."
Article title : Life unworthy of life
"The phrase "life unworthy of life" (German: Lebensunwertes Leben) was a Nazi designation for the segments of the populace which, according to the Nazi..."
Article title : Life After Life
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Article title : That's Life!
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Article title : This Life
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Article title : The Life of a Showgirl
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Article title : That's Life
"that's life in Wiktionary, the free dictionary. That's Life may refer to: That's Life! (film), a 1986 comedy-drama directed by Blake Edwards That's Life (1980..."
Article title : Extraterrestrial life
"Could life have arisen elsewhere? What are the requirements for life? Are there exoplanets like Earth? How likely is the evolution of intelligent life? More..."
Article title : Tomodachi Life
"Tomodachi Life, known in Japan as Tomodachi Collection: New Life, is a 2013 social simulation game developed and published by Nintendo for the Nintendo..."

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