Journal of Modern Physics, 2011, 2, 595-601
doi:10.4236/jmp.2011.226069 Published Online June 2011 (http://www.SciRP.org/journal/jmp)
Entropy Production and the Origin of Life
Karo Michaelian
Instituto de Física, Universidad Nacional Autónoma de México, Cto. de la Investigación Científica,
Cuidad Universitaria, Mexico City, Mexico
Received January 28, 2011; revised April 22, 2011; accepted April 25, 2011
Abstract
All irreversible processes arise and persist to produce entropy. Entropy production is not incidental to such
processes, but rather the very reason for their origin and persistence. Here we take such a thermodynamic
perspective on the origin of life, recognizing that entropy production is not only the vital force of life, but the
fundamental link between life in the biosphere today and its origin in the Archean. Today the greatest en-
tropy production in the biosphere is due to visible photon absorption and dissipation into heat by organic
material in liquid water and the subsequent degradation of the established heat gradient through the water
cycle. Following this link back in time to the Archean environment leads to a suggestion for a mechanism for
the origin of life based on UV photon absorption and dissipation by RNA and DNA.
Keywords: Origin of Life, Entropy Production, RNA, DNA, Non-Equilibrium Thermodynamics, UVTAR
1. Introduction
In 1871, Charles Darwin in a private letter to his friend,
the English botanist and explorer Joseph D. Hooker,
suggested that life may have had a chemical origin [1].
However, for lack of an in depth analysis, or perhaps to
avoid perturbing the conservative public of his time,
Darwin wrote in his 1859 book “On the Origin of Spe-
cies” that, “God first blew life into one or a few forms,
and then evolution took over”. One hundred years later,
inspired by Oparin’s 1924 suggestion of a material origin
of life [2], Miller and Urey [3] showed that subjecting
what was then the best hypothesis for the gasses of the
prebiotic atmosphere (methane, ammonia, water, and
carbon dioxide) to electric discharge was sufficient to
produce at least 11 of the 20 then known amino acids
making up the proteins of life (actually there are 22
known amino acids of life). Since then, many other
similar experiments have demonstrated abiogenic routs
to, not only the amino acids, but also to the nucleic acid
bases, the ribose-like sugars, and the polyphosphates; the
basic constituents of RNA and DNA, the probable first
molecules of life [4,5].
Although both single and double strand RNA and
DNA can now be readily abiotically synthesized and
manipulated in vitro, more than 50 years of experimenta-
tion since the first Miller experiments has been insuffi-
cient to produce a replicating life de novo in the labora-
tory. The difficulty has been to demonstrate self-replica-
tion of RNA or DNA without the aid of the enzymes and
the free energy containing molecules such as ATP. To-
day, in even the simplest archaea and bacteria, replica-
tion is carried out with the aid of a large number of en-
zymes, encoded for in the DNA and produced in the ri-
bosome organelles of the complex cell. How then could
RNA or DNA replicate, at the very beginnings of life,
without the availability of these enzymes and the free
energy containing molecules? This problem has been
studied extensively with limited progress to date [4,5].
The most promising avenues led to the premise that RNA
was the first molecule of life, which led to a paradigm
now known as the “RNA World”. Indications that RNA
might have played a part in its own replication are vari-
ous; 1) the observed ability of RNA to self-splice [6], 2)
to act as a rybozyme; i.e. as a polymerase catalyst in
template assisted polymerization of itself [7,8], and 3) its
ability to act as a catalyst for the formation of peptide
bonds between amino acids [9].
Many theories have been proposed, and experiments
performed, in the search for the origin of life (for an
overview of the recent history see Kumar [10]). Most
experiments have considered near-equilibrium conditions
in the presence of mineral or clay catalysts, and look for
the appearance of an auto-catalytic chemical cycle.
However, the expectation of observing the origin of an
irreversible process such as life, without due considera-

596 K. MICHAELIAN
tion, or even recognition, of its thermodynamic function
of entropy production, is erroneous. All irreversible
processes arise and persist to produce entropy. This is
true of the burning flame of a candle, hurricanes, the
water cycle, and, of course, life itself. Irreversible proc-
esses will arise, couple, and persist whenever the global
entropy production of the Universe increases, and as long
as all natural laws and constants are respected [11].
Boltzmann [12] (1886) understood the implications of
this when, only 27 years after the publication of “On the
Origin of Species”, he wrote “The general struggle for
existence of animate beings is therefore not a struggle for
raw materials—nor for energy which exists in plenty in
any body in the form of heat—but a struggle for entropy,
which becomes available through the transition of energy
from the hot sun to the cold earth”. Entropy production is
not incidental to the process of life; the process of life
obtains its vitality and reason for being through entropy
production.
If entropy production is the driving force of life, then
this, of course, must have been the case since its very
beginnings. Entropy production is thus a link that perme-
ates the entire evolutive history of life on Earth. It is then
of interest to follow this link back in time, starting from
the mechanism of entropy production employed by life
today and searching for an analogy which could have
been operating at the very beginnings of life, involving
the probable first molecules of life, RNA and DNA, and
the prevalent ambient conditions. Such logic leads to a
new paradigm for the origin of life, consistent with what
we have learned so far, but incorporating these new
thermodynamic elements which lend direction to life’s
origin.
2. The Thermodynamic Function of Life
By far the most abundant biomass at the surface of the
Earth consists of plants and cyanobacteria [13]. Photo-
trophic plants and cyanobacteria over land and water
have traditionally been considered as the first link of a
food chain, or, as the base of an ecological pyramid with
the highest predators residing at its pinnacle. However,
from a thermodynamic viewpoint, plants and cyanobac-
teria do much more than supply the rest of life with
free-energy rich organic materials obtained through pho-
tosynthesis. In fact, all photosynthetic production uses
less than 0.1% of the free energy available in sunlight
absorbed by the leaves of the plant [14] or absorbed by
cyanobacteria. By far the greatest amount of free energy
in sunlight incident on the plant is consumed in transpi-
ration. Water is drawn up by the roots and evaporated
from the leaves of plants and thereby delivered into the
global water cycle. On the ocean surface and over moist
land surfaces, cyanobacteria absorb sunlight and dissi-
pate this light into infrared wavelengths that can be read-
ily absorbed by water, thereby increasing the evaporation
from the oceans and land and thus also contributing to
the global water cycle [15].
Animals, by degrading the free energy available in
plant and cyanobacterial matter, also augment the en-
tropy production of the Earth in its interaction with its
solar environment. However, this direct entropy produc-
tion is insignificant compared to the increase in entropy
production afforded indirectly to the plants through their
interaction with animals. Animals stimulate plant growth
and dissemination by spreading nutrients and seeds, and
by providing a vehicle for cross fertilization. Their dig-
ging and stirring brings oxygen and nitrogen into the soil
and water, impacting significantly primary productivity.
The most important thermodynamic function of the ani-
mals is therefore to ensure that the plants and cyanobac-
teria are well cared for and able to spread into new areas,
thereby attaining maximal entropy production through
photon dissipation coupled to evapotranspiration [15].
3. Entropy Production Due to Life Today
The plants and cyanobacteria of today absorb light over a
wide range of the most intense part of the Sun’s spec-
trum. Although the chlorophyll (a) and chlorophyll (b)
molecules have narrow absorption spectra, peaking
around 430 nm (in the blue) and 662 nm (in the red),
there exist many accessory pigments, or antenna type
molecules such as the carotenoids, flavonoids, and beta-
lains, that allow the plant to absorb over a much wider
range of the solar spectrum. These accessory pigments
appear to have little physiological role in photosynthesis
or in plant metabolism and in fact release most of the
absorbed light energy as heat rather than in chemical
transformations. Even the absorption of light by chloro-
phyll itself is subjected to many non-photochemical
quenching routs having nothing to do with photosynthe-
sis [16]. This leads to the interesting result that the
photo-absorption spectrum of both plants and cyanobac-
teria is significantly more extent than the photo-activa-
tion spectrum of photosynthesis.
Recently, a large variety of related molecules known
as microsporine-like amino acids (MAAs), which absorb
over the UVA and UVB region of the Sun’s spectrum,
have also been discovered in plants and phytoplankton
[17]. A single plant may contain many MAAs, leading to
an approximately flat absorption spectrum in the near
ultraviolet. The existence of these pigments and antenna
type molecules has hitherto been assigned as rudiments
of the evolutionary development of the photosynthetic
apparatus [18], principally as agents that protect (or,

K. MICHAELIAN
597
protected) the photosynthetic apparatus from damage
caused by an excess of photons, or photons of very high
energy. However, since photosynthesis contributes little
to the total entropy production of plants or cyanobacteria,
while transpiration contributes overwhelmingly, a more
likely thermodynamically consistent explanation is that
such pigments and antenna molecules are still very rele-
vant, acting primarily to aid in photon dissipation and -
transpiration, the primary entropy producing process of a
plant or cyanobacteria.
An interesting experimental result corroborating this
idea—that the primary thermodynamic function of life
today is entropy production through photon dissipation
and transpiration—has been obtained by Wang et al. [19].
They find vanishing derivatives of transpiration rates
with respect to leaf temperature and CO2 flux, suggesting
a maximum transpiration rate in these variables for
plants. In fact, they found that the particular partition of
latent and sensible heat fluxes to be such that it leads to a
leaf temperature and leaf water potential giving maximal
transpiration rates, and thus maximal production of en-
tropy. Although such an optimality principle has fre-
quently been suggested to be operating for the process of
photosynthesis, to the author’s knowledge, no empirical
evidence has so far confirmed this. Plants, therefore, ap-
pear to have evolved for optimizing transpiration rather
than photosynthesis.
4. Entropy Production Due to Life in the
Archean
Can entropy production through photon dissipation and
the subsequent transpiration of water by life today be
traced back in time to the very beginnings of life? Since
life is an open irreversible process dependent on external
thermodynamic forces (in particular, the solar photon
flux), to answer this, it is first necessary to determine the
environmental conditions existing at the surface of the
Archean Earth some 3.8 billion years ago. A discussion
of the most probable, given present knowledge, ambient
conditions of the prebiotic Earth relevant to the begin-
nings of life have been given elsewhere [20]. Here we
summarize only the most important aspects relevant to
the proposed hypothesis.
The surface of the Archean Earth was initially very hot,
due to the heat of accretion, high internal radioactivity,
and asteroid bombardment. The surface temperature fell
to roughly (70 ± 15)˚C during the 3.5 - 3.2 Ga era [21],
as determined from geochemical evidence in the form of
18O/16O ratios found in cherts of the Barberton green-
stone belt of South Africa. The atmosphere was probably
composed of nitrogen, carbon dioxide and reducing
gases containing a lot of hydrogen. The photon absorp-
tion spectrum of such an atmosphere, taking into account
the aldehydes formed by UV photochemical reactions on
these gases [22], would have lead to an atmospheric
window of transparency in the ultraviolet of between
approximately 240 nm and 290 nm [20,22]. In fact, de-
tailed simulations of the Archean atmosphere, consider-
ing the light absorption and scattering properties of these
gases, as well as the fact that the young Sun was much
more intense in the ultraviolet during the Archean, show
that the amount of ultraviolet light at 254 nm reaching
the Earth’s surface during the Archean could have been
up to 1031 times that of what it is today [23].
The high surface temperature of the Archean Earth
would also imply a greater amount of water vapor in the
atmosphere than today. More prevalent volcanic erup-
tions would also mean a larger amount of sulfur dioxide
in the atmosphere. UV photochemical reactions on these
gases would have produced a thin layer of sulfuric acid
clouds that would have been highly reflective in the visi-
ble, as on Venus today. It is then probable that an en-
thropically important part of the Sun’s spectrum reaching
the surface of the Earth would have been that in the ul-
traviolet between roughly 240 nm and 290 nm.
Now, it is an interesting fact that the nucleic acid bases,
adenine, thymine, cytosine, guanine, and uracil absorb
very strongly just at these wavelengths (peak absorption
of DNA at 260 nm) and in water dissipate the photon-
induced excitation energy directly and rapidly (10–12 s) to
heat (vibrational and rotational molecular motion) of the
surrounding water [24-27] (see Figure 1). The nucleic
acid bases are thus excellent entropy producing mole-
cules in the ultraviolet region of the Sun’s spectrum.
During the Archean, these molecules would have played
a thermodynamic role analogous to the chlorophyll
molecule and other pigments of today in dissipating the
high energy photons reaching the Earth’s surface and
catalyzing the water cycle.
Under the very high flux of UV light prevalent during
the Archean, the absorption and rapid non-radiative de-
cay characteristics in the ultraviolet of the nucleic acid
bases would have given these a selective advantage over
other organic molecules more prone to photolysing or
photochemical reactions [22]. The nucleic acid bases
would then fair better in the competition for the more
basic constituent molecules needed for their synthesis.
Other molecules which could attach themselves to the
nucleic acid bases would also obtain, by association,
significant UV protection, and thus selective advantage
[28]. Such molecules might have included adenosine
triphosphate (ATP) and the five nucleotides. However,
over and above the selective advantage of UV protection,
the important ability of these molecules to absorb and
dissipate into heat a high energy photon would promote

598 K. MICHAELIAN
(a)
(b)
Figure 1. (a) Absorption maximum in the ultra violet at 260 nm
of single strand and double helix DNA. The difference,
marked by the double arrow, is known as hypochroism and
is due to the random orientation of the bases in single
strand DNA (or RNA); (b) Rapid non-radiative decay of the
excited bases of DNA when in water (within a pico-second).
Reproduced with permission from Pecourt et al. [27].
their existence and proliferation as a thermodynamic
imperative. A non-equilibrium chemical rout to the pro-
duction, maintenance and multiplication of these mole-
cules would have been sought out by Nature simply due
to their entropy producing characteristics in the intense
UV environment of Archean Earth [20].
5. Multiplication of RNA and DNA without
the Aid of Enzymes
Molecules containing the UV absorbing and dissipating
nucleic acid bases would thus gradually have accumu-
lated on the surfaces of the shallow seas; their survival
being favored by their rapid and non-radiative excited
state decay dynamics, and their multiplication being fa-
vored by the increase in entropy production afforded to
the Earth within its solar environment. However, the
most difficult question remains: Just how could their
multiplication have occurred without the aid of enzymes
or free energy containing molecules? Here I suggest that
the ambient conditions of Archean Earth could have
played an important part in the replication of primordial
RNA or DNA.
Given a large accumulation of nucleic acid bases and
other derivatives of the bases, protected from UV lysing
and photochemical reactions, at the sea surface, it is rea-
sonable to expect at least some polymerization of the
nucleotides. Polymerization would, in fact, be thermo-
dynamically driven since UV excited single strand RNA
and DNA is more apt to decay through rapid intersystem
crossing channels, and therefore be less prone to
photolysing or photoreactions, than are the isolated bases
which can loose efficiency by decaying to a much longer
lived 1* n

state [29].
If the surface of the Earth was initially very hot, fal- ling
to a temperature of (70 ± 15)˚C during the 3.5 - 3.2 Ga era
[21], then it is probable that just before the very begin-
nings of life at approximately 3.8 Ga, the surface tem-
perature of the seas would have been above the de-
naturing temperature of RNA and DNA (generally
around 85˚C, but dependent on the amount of guanine-
cytosine pairs, which tend to increase the denaturing
temperature). Continued cooling of the seas would have
led to a situation at which the surface temperature of the
sea at night would have been below the denaturing tem-
perature of at least some segments of RNA and DNA,
allowing these segments to act as templates for the con-
struction of a complimentary segment overnight. As the
sun rose, the surface of the seas would again heat up
through ultraviolet, visible, and infrared light absorption,
such that by late afternoon the temperature of the surface
water would be sufficient to denature double strand RNA
or DNA. In this way, new templates would be formed for
continued replication. An important part of the heating of
the surface water in the local neighborhood of the double
strand RNA/DNA would have come from the direct ab-
sorption and rapid dissipation of UV photons by the
bases within the 240 to 290 nm region [20].
The day-night temperature cycling of the sea surface
around the denaturing temperature of RNA/DNA, along
with the direct absorption and dissipation of a UV photon,
would have provided a mechanism for replication similar
to that which is in general use today in the laboratory,
known as “polymerase chain reaction” [30]. The mecha-
nism postulated here for early replication may be called

K. MICHAELIAN
599
“UV and Temperature Assisted Replication (UVTAR)”
and is depicted in Figure 2.
very intense UV radiation. As the hydrogen containing
prebiotic molecules gradually became depleted from the
Archean atmosphere, the skies would have begun to clear
of the aldehydes and sulfuric acid clouds, allowing more
visible radiation to penetrate to the surface. The normal
evolution of solar type stars implies a Sun brightening in
the visible and dimming in the ultraviolet. Further in-
creases in entropy production would thus have come
from dissipating more light towards the visible region of
the spectrum. This would have meant the gradual selec-
tion of RNA or DNA coding for pigments that absorbed
and dissipated in the UVA and UVB spectrum, such as
the microsporine pigments based on the most readily
abiogenically synthesized amino acid glycine, and even-
tually pigments in the visible, such as the chlorophyll
molecule, based on the porphyrins.
As the seas continued to cool, those RNA/DNA seg-
ments with lower denaturing temperature, or with sec-
tions coding for a simple denaturing enzyme, could con-
tinue replicating while the rest of the double strands
would become locked, unable to denature, and thus be
effectively removed from competition for the nucleotides.
Coding for a simple denaturing enzyme may thus have
been the first utility of information storage for RNA or
DNA. As the seas cooled further, continued entropy
production would require the natural selection of RNA or
DNA segments coding for still more complex enzymes
that could perform the denaturing at still cooler tempera-
tures, or for antenna type molecules that could dissipate
more of the solar spectrum and deliver the resultant heat
locally. RNA/DNA segments that coded for enzymes
that could attract and then polymerize nucleotides on
existing strands (for example, polymerase-type) would
become more favored still as the seas cooled further.
In contrast to the RNA-first theory on the origin of life,
in the present theory, information content and fidelity of
replication were not prerequisites to the beginning of life
since replication was afforded by the UVTAR mecha-
nism without the need for enzymes, at least while envi-
ronmental conditions were favorable. However, as the
ambient conditions at the Earth’s surface moved ever
further from those relevant for UVTAR, information and
fidelity of replication became ever more important to the
maintenance and multiplication of the photon dissipating
molecules, and thereby to global entropy production of
Earth.
Thus may have begun the first steps of evolution
through natural selection. The tendency of Nature to
discover new routs to greater entropy production, often
building on existing routs, under the imposed solar pho-
ton flux over the Earth, was, and still is, the driving force
behind evolution. Entropy production in the early days of
life was afforded by the remarkable absorption and dis-
sipation characteristics of single strand RNA/DNA ex-
isting in abundance at the surface of the seas exposed to
Figure 2. (a) Double strand RNA/DNA floats on the Archean sea surface in the early morning hours. (b) By late afternoon the
sea surface temperature heats up beyond the denaturing temperature of RNA/DNA and the strands separate, in part due to
the direct absorption of UV photons by RNA/DNA; (c) Over night, the sea surface temperature cools to below the denaturing
temperature and single strand RNA/DNA act as template for the formation of a complimentary strand. The entire replication
process is driven by entropy production resulting from the absorption and dissipation of UV photons.

K. MICHAELIAN
600
6. Conclusions
Entropy production is the link that permeates all of life
from its humble beginnings in the Archean to the vast
and complex ecosystems of today. Understanding this
thermodynamic function of life has allowed us to trace
this link back in time and suggest an analogous entropy
producing mechanism involving the most probable first
molecules of life, RNA and DNA. Absorption and dissi-
pation of UV light around 260 nm was probably the pri-
mordial thermodynamic function of the first RNA or
DNA single strand molecules floating on the ocean sur-
face. The remarkable UV absorption and dissipation
characteristics of the nucleic acid bases afforded the nu-
cleotide polymers protection from photo-lysing and pho-
tochemical reactions, allowing them to accumulate to
significant concentrations on the surfaces of the Archean
seas. Their entropy producing function for the Earth in
its solar environment promoted their maintenance and
multiplication. As the temperature of the seas fell to be-
low the denaturing temperature of certain RNA or DNA
segments, these could begin to act as templates for the
formation of complimentary strands during the cooler
periods overnight. As the seas cooled further, those seg-
ments which happened to code for simple denaturing
enzymes or antenna type molecules would find greater
advantage in an ever colder sea. The cooling of the ocean
surface was thus probably the force that stimulated the
information content and corresponding reproductive fi-
delity of RNA and DNA.
As the light conditions of the Earth’s surface changed,
as a result of combined biotic, atmospheric, and solar
evolution, entropy production was driven towards the
dissipation of longer wavelengths of greater intensity
closer to the visible region of the Sun’s spectrum, which
eventually led to the coding for chlorophyll and other
contemporary pigments. The tendency towards evolution
of new pigments covering an ever greater region of the
Sun’s spectrum remains to this day; old conifer forests of
climax ecosystems are almost black and absorb and dis-
sipate more incident light than any other biotic or abiotic
system on the surface of the Earth. The primary function
of animals is to facilitate the maintenance and spread of
the photon dissipating pigments throughout the surface
of the Earth.
The origin of life was contingent on the increase in the
entropy production it afforded Earth under the existent
environmental conditions. Tracing the link of entropy
production through photon dissipation and transpiration
back in time to the Archean, where UV dissipation took
precedent over visible dissipation, leads to, a thermody-
namic reason for the origin of life on Earth.
7. Acknowledgements
The financial assistance of DGAPA-UNAM, grant num-
bers IN118206 and IN112809, is greatly appreciated.
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