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False-color Cassini radar mosaic of Titan's north polar region; the blue areas are lakes of liquid hydrocarbons. "The existence of lakes of liquid hydrocarbons on Titan opens up the possibility for solvents and energy sources that are alternatives to those in our biosphere and that might support novel life forms altogether different from those on Earth."—NASA Astrobiology Roadmap 2008 [1]
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 ...
[4] [5] Plate tectonics are needed for life over a long time span, and carbon-based life is important in the plate tectonics process. [6] Iron- and sulfur-based Anoxygenic photosynthesis life forms that lived from 3.80 to 3.85 billion years ago on Earth produced an abundance of black shale deposits. These shale deposits increase heat flow and ...
This form of biosignature is called an "agnostic biosignature" because it is independent of the form of life that produces it. It is widely agreed that all life–no matter how different it is from life on Earth–needs a source of energy to thrive. [71] This must involve some sort of chemical disequilibrium, which can be exploited for metabolism.
Non-cellular life, also known as acellular life, is life that exists without a cellular structure for at least part of its life cycle. [1] Historically, most definitions of life postulated that an organism must be composed of one or more cells, [2] but, for some, this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements.
Basic chemical ingredients of life – the carbon-hydrogen molecule (CH), the carbon-hydrogen positive ion (CH+) and the carbon ion (C+) – can be produced by ultraviolet light from stars. [93] Complex molecules, including organic molecules, form naturally both in space and on planets. [ 94 ]
A scenario is a set of related concepts pertinent to the origin of life (abiogenesis), such as the iron-sulfur world.Many alternative abiogenesis scenarios have been proposed by scientists in a variety of fields from the 1950s onwards in an attempt to explain how the complex mechanisms of life could have come into existence.
All life forms require certain core chemical elements for their biochemical functioning. These include carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—the elemental macronutrients for all organisms. [135] Together these make up nucleic acids, proteins and lipids, the bulk of living matter. Five of these six elements comprise the ...