Carbon-based life

Carbon-based life
Left: a depiction of an light-induced animated carbon-based molecule (retinal); which is similar to a human, also a light-induced animated carbon-based molecule, a CHNOPS+22 molecule specifically. Right (top): a carbon element tattoo on a human, oft-conceptualized as a form of "carbon-based life", who states: “I am a biochemist, studying to be a molecular biologist, the tattoo is carbon on the periodic table of elements. Since all living things on this planet at least are carbon based, from a chemical standpoint, it doesn’t get much more basic than carbon. Hence the tattoo.” –ErinExternal link icon (c)(2008)
In science, carbon-based life, or "carbon-based organism", refers to the 1950s model that humans and animate things similar to humans are based compositionally, structurally, and or mentally on the element carbon.

The versatilities of the bonding geometries and dynamics of the carbon atom, with its four available valencies or bonding sites, is what gives carbon-based molecules the ability to be animated when exposed to light and various other reaction environments.

Overview
In 1934, Harold Blum, in his chemical peneplanation theory, discussed the possibility of ammonia (NH3) based life, in comparison to water (H2O) based life, seen on earth.

In 1950s, the term “carbon-based”, in contrast to silicon-based theories of life, began to appear in discussions of the possibility of life on Mars; the following begin one example:

“Our knowledge of physics, therefore, seems to tell us that living things anywhere in the universe must depend either upon carbon or upon silicon. Carbon-based life must be essentially similar to our own; there is no room for doubt upon that.”
— Author (1955), “Article”, Science Digest (Ѻ), Vol 37

In 1967, people were citing Harold Morowitz per the assertion that “that if there is any life on Mars it is based on carbon. The chemical composition of the biosphere on Mars should be analogous to the terrestrial biosphere, though it may not be identical.” (Ѻ) The term ‘carbon-based life’, soon thereafter became a popular phrase in extraterrestrial life search circles, on the hypothesis that extraterrestrial life, if it exists, must be constructed primarily from carbon. [1]

CHNOPS-based
The 19th century model of a human as a carbon-based organism, eventually was supplanted by the CHNOPS-based organism model; which is outlined below:

Carbon-based to CHNOPS-based

(add discussion)

Light-induced movement
See main: Retinal molecule, Induced movement
In the absence of light, the carbon–carbon bond (red) at carbon 11 adopts a cis configuration and the chromophore adopts a bent structure (all of the other C=C bonds are trans). The two methyl groups (CH3, blue) at carbon atoms 9 and 13 point away from each other as indicated by the arrows. When exposed to light, retinal absorbs photons and the double bond at carbon 11 isomerizes from cis to trans and the now ‘all-trans’ retinal molecule straightens. This process also aligns the two CH3 groups, which now point in the same direction away from the main carbon chain. In vivo, the straightening of the retinal chromophore causes it to be released from the protein to which it is attached, because it no longer fits in the binding site. This, in turn, causes a change in the shape of the protein, which triggers a cascade that ultimately results in an electrical impulse being sent along the optic nerve, leading to visual perception. [2]

Quotes
The following are related quotes:

“It is well known that carbon is required to make physicists.”
— Robert Dicke (1961), “Dirac’s Cosmology and Mach’s Principle” [1]

References
1. Venter, J. Craig. (2006). What We Believe But Cannot Prove (pg. 21). Harper.
2. Liu, Zheng, Yanagi, Kazuhiro, Suenaga, Kazu, Kataura, Hiromichi, and Iijima, Sumio. (2007). “Imaging the Dynamic Behavior of Individual retianal Chromophores Confined inside Nanotubes” (figure 1), Nature nanotechnology, 2: 422-25.
3. Dicke, Robert H. (1961). “Dirac’s Cosmology and Mach’s Principle” (abs)(Ѻ), Nature, 192:440, Nov.

External links
Carbon-based life – Wikipedia.
Carbon chauvinism – Wikipedia.
Hypothetical types of biochemistry – Wikipedia.


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