Origin of life

In a scientific context, in order to discuss, much less discover, the origin of life, we must first answer the question, "What is Life?" We can pose that question more coherently by asking, "What essential processes underpin the activity of living?" Knowing the fundamental physico-chemical processes that underpin the activity of all living systems gives us a starting point for making observations, generating hypotheses, and performing experiments in the search for life’s origin — for those processes somehow must have given rise to the first cells, the basic building blocks and working units of all living things on Earth. We must discover the characteristics of the earliest cells from which all current living things descended.

Because we must look backward to a time nearly four billion years ago, we will find little, but not nothing,  in the way of remains to examine. We can hypothesize, and submit those hypotheses to existing knowledge of earth's early conditions and to experiments attempting to reproduce those conditions. We can narrow our hypotheses and search-paths by dissecting out the most basic and essential physico-chemical processes common to all known living things — the universal biophysics,   biochemistry  and metabolism  of living things — because as conserved core processes they have the greatest probability of embryonic status.

We search for the origin of a system we recognize as living in virtue that it has the informational content and information-processing ability to remain as a compartmentalized near-steady-state self-organized dynamical system of hierarchical robust modular molecular networks, where the networks operate autonomously in their own behalf, to offset responses to perturbations, adapt to changing conditions, and facilitate the system's reproducing itself. We search for the origin of a system enabled by influx of energy and matter and by a more than compensatory efflux of waste (disorder), which thereby permits sustaining and exploiting a dynamically organized state far from the equilibrium state of randomness. Finally, we search for the origin of a system capable, through its self-reproductive ability, of participating in the evolutionary processes  that enable transgenerational evolution of the species to which it belongs, adapting to changing environments.

Scientists do not know the origin of life on Earth. They do have pieces of the puzzle, however, and many conflicting plausible scientific scenarios.

Pre-biotic chemical evolution

Pre-biotic chemical evolution as prelude to origin of living systems. See, for example:

• Dyson 1982
• Post 1990
• Galimov 2004
• Danchin 2007
• Sayer 2006
• Deamer 2006
• Szathmary 2006
• Davies 2000

The RNA World

• Koonin
• Baaske

References

External links

• Geological timescale.

• Origins of the Eukarya.

• Hadean Eon

Further reading

• Vetsigian, K et al. (2006) Collective evolution and the genetic code Proc Natl Acad Sci USA 103:10696–1070. PMID 1681888

• Goldenfeld N Woese C (2007) Essays: Connections. Biology's next revolution The emerging picture of microbes as gene–swapping collectives demands a revision of such concepts as organism, species and evolution itself. Nature 445:369 (25 January 2007) doi:10.1038/445369a

• Forterre P (2006) Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: A hypothesis for the origin of cellular domain PNAS 103:3669-3674

• Davies P. (2000) The Fifth Miracle: Search for the Origin and Meaning of Life. Simon & Schuster ISBN 978-0684863092
  

• From The New York Times Book Review, by Lee Smolin: "If you are going to read only one book on the origin of life, seriously consider this one. From Scientific American: "His thesis is that 'the first terrestrial organisms lived deep underground, entombed within geothermally heated rocks in pressure-cooker conditions.' Davies also looks at the theories that life began by chemical assembly in a watery medium and that it came to the earth from space in the form of already viable microbes--the panspermia hypothesis.

See also

• Life