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 universal 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 earliest 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 spatially 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 thermodynamically open system enabled by influx of energy and matter and by a more than compensatory efflux of waste (disorder), which thereby complies with the second law of thermodynamics and 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.

The history of scientific 'origins of life' thinking

"A quantum recipe for [the origin of] life"

Theoretical physicist, cosmologist, astrobiologist and science popularizer, Paul Davies, has imagined a "quantum recipe" for the origin of life:

To take up [physicist Erwin] Schrödinger's suggestion [....that quantum mechanics, or some variant of it, would soon solve the riddle of life....], a radical solution to the problem, 'What is life?' could be that quantum mechanics enabled life to emerge directly from the atomic world, without the need for complex intermediate chemistry. Life must have a chemical basis: organic molecules provide the hardware for biology. But what about the software?

The software, Davies argues, resides in quantum information. "....to get life started all you need is to replicate information." He argues that, at the quantum level of reality, information processing can proceed much more rapidly, by comparison presumably with chemical reactions, can achieve gains in information processing performance through such quantum capabilities as tunneling, superposition, and entanglement. He proceeds to conjecture on the replication of the information in an atomic system through a series of interactions, the information in the systems residing possibly in binary form "....making use of the spin orientation of an electron or atom for example." He asserts that quantum mechanics can thus make discrete 'genetic' information.

Davies refers to his conjectured quantum information replicator as "atomic Adam" and speculates on the best environments where some such "atomic Adams" might exist. He argues that when a population of such quantum information replicators arises, expect variation in the fidelity of replication because of the quantum uncertainty principle. Given variation, an evolution of the information by means of darwinian-wallacean natural selection, or survival of the fittest replicators, might occur in the prevailing environment. "....and the great darwinian game could begin."

Davies then asks, given the reality of quantum information replicators in a darwinian reproductive-type domain, how 'organic' life arose? He supposes that "At some stage, quantum life could have co-opted large organic molecules for back-up memory." How that 'great leap' might have occurred Davies offers no plausible description, except to say that information in one medium does not preclude translation to other media. Not that the medium of organic chemistry strays far from the underpinnings of its quantum chemical medium.

Once that transfer of information occurs — from quantum to chemical information — expect a loss in rapidity of information processing, but also expect greater stability in the organic molecules, and greater versatility, and greater complexity. Those compensations might ensure the dominance of organic living systems, given natural selection, and its enabling of the exploitation of diverse environments.

Davies seems to worry most about the issue of complexity of quantum life:

How complexity emerges in quantum systems is a subject still in its infancy, but the principles involved could be illuminated by applying algorithmic complexity theory to quantum information theory.

We might ask the question how much complexity must precede the transfer of quantum information to organic molecular information, given the potential for natural selection, and other evolutionary forces — not to mention autopoiesis — to enable the emergence of organic complexity?

Pre-biotic chemistry and the origin of organic molecules

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

• Dyson 1982
• Post 1990
• Davies 2000
• Galimov 2004
• Danchin 2007
• Sayer 2006
• Deamer 2006
• Szathmary 2006
• Phil Berardelli 2008
• Robinson R (2005)
• Protocells: Bridging Nonliving and Living Matter. Edited by Steen Rasmussen, Mark A. Bedau, Liaohai Chen, David Deamer, David C. Krakauer, Norman H. Packard and Peter F. Stadler. ISBN 978-0-262-18268-3.
• Follmann,H.; Brownson,C. (2009) Darwin's warm little pond revisited - from molecules to the origin of life. Naturwissenschaften 96(11):1265-1292. In this review, we have concentrated on experimental and theoretical research published over the last two decades, which has added a wealth of new details and helped to close gaps in our previous understanding of this multifaceted field.

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