This web site introduces the reader to a new theory of the origin of life, originally proposed by Dr. Karo Michaelian of the National Autonomous University of Mexico (UNAM) in 2009 (http://arxiv.org/abs/0907.0042 and http://www.earth-syst-dynam.net/2/37/2011/esd-2-37-2011.html). Unlike traditional theories that require some sort of accidental auto-catalytic chemical cycle, this theory is based on the realization that life, like all irreversible processes, arose and persists to produce entropy. The most relevant general thermodynamic potential available at the surface of the earth during the Archean would have been the solar UV photon flux within the 220 to 280 nm range. The proposed theory suggests that first nucleobases, and then RNA and DNA, would have proliferated on the Earth’s surface during the Archean due to their propensity to dissipate UV photons into heat, particularly when in water. This theory is neither “replication first” nor “metabolism first”, it is rather “dissipation first”.
Any model for the origin of life must take into account the fact that life is an irreversible thermodynamic process which arises and persists because it produces entropy. Entropy production is not incidental to the process of life, but rather the fundamental reason for its existence. Present day life augments the entropy production of Earth by dissipating high energy photons into heat and catalysing the water cycle through evapotranspiration. Michaelian argues that if the thermodynamic function of life today is to produce entropy through photon dissipation and coupling with the water cycle, then this probably was its function at its very beginnings. It turns out that both RNA and DNA when in water solution are very strong absorbers and extremely rapid dissipaters of ultraviolet light within the 200–300 nm wavelength range, which is just that part of the sun’s spectrum that could have penetrated the dense prebiotic atmosphere. Cnossen et al. have shown that the amount of ultraviolet (UV) light reaching the Earth’s surface in the Archean eon could have been up to 31 orders of magnitude greater than it is today at 260 nm where RNA and DNA absorb most strongly. Absorption and dissipation of UV light by the organic molecules at the Archean ocean surface would have significantly increased the temperature of the surface skin layer and led to enhanced evaporation and thus to have augmented the primitive water cycle. Since absorption and dissipation of high energy photons is an entropy producing process, Michaelian argues that non-equilbrium abiogenic synthesis of RNA and DNA utilizing UV lightwould have been thermodynamically favored.
A simple mechanism that could explain the replication of RNA and DNA without resort to the use of enzymes could also be provided within the same thermodynamic framework by assuming that life arose when the temperature of the primitive seas had cooled to somewhat below the denaturing temperature of RNA or DNA (based on the ratio of 18O/16O found in cherts of the Barberton greenstone belt of South Africa of about 3.5 to 3.2 Ga., surface temperatures are predicted to have been around 70±15 °C, similar to RNA or DNA denaturing temperatures). During the night, the surface water temperature would drop below the denaturing temperature and single strand RNA/DNA could act as a template for the formation of double strand RNA/DNA. During the daylight hours, RNA and DNA would absorb UV light and convert this directly to heat the ocean surface, thereby raising the local temperature enough to allow for denaturing of RNA and DNA. The copying process would have been repeated with each diurnal cycle. Such a temperature assisted mechanism of replication bears similarity to polymerase chain reaction (PCR), a routine laboratory procedure employed to multiply DNA segments. Since the proposed mechanism also depends on UV absorption and dissipation, it has been called Ultraviolet and Temperature Assisted Reproduction (UVTAR). Michaelian suggests that the traditional origin of life research, that expects to describe the emergence of life from near-equilibrium conditions, is erroneous and that non-equilibrium conditions must be considered, in particular, the importance of entropy production to the emergence of life.
Since denaturation would be most probable in the late afternoon when the Archean sea surface temperature would be highest, and since late afternoon submarine sunlight is somewhat circularly polarized, the homochirality of the organic molecules of life can also be explained within the proposed thermodynamic framework.
(see the Homochirality button, this web site)