PLEASE NOTE:


*

CCNet SPECIAL: ASTROBIOLOGY & THE ORIGIN OF LIFE
------------------------------------------------


(1) INTRODUCTION
    Paul Davies <pcwd@camtech.net.au>

(2) THE MOTHER OF ALL QUESTIONS
    NATURE, 8 Oct 1998
http://www.physics.adelaide.edu.au/itp/staff/pcwd/reviews/bengtson.html

(3) INTERSTELLAR GRAINS AS AMINO ACID FACTORIES & THE ORIGIN OF LIFE
    W.H. Sorrell, UNIVERSITY OF MISSOURI

(4) CARBONACEOUS MICROMETEORITES & THE ORIGIN OF LIFE
    M. Maurette, CTR

(5) THE BIOLOGICAL POTENTIAL OF MARS, THE EARLY EARTH & EUROPA
    B.M. Jakosky*) & E.L. Shock, UNIVERSITY OF COLORADO

(6) ELECTROMAGNETIC ORIGIN OF LIFE
    I. Jerman, INSTITUE OF BIOELECTROMAGNET & NEW BIOLOGY

(7) WHAT EXACTLY IS LIFE?
    P.L. Luisi, ETH ZENTRUM

(8) SELF-REPLICATING ASYMMETRICAL FROZEN PROBABILITY
    M.L. Glassman & A. Hochberg, HEBREW UNIVERSITY JERUSALEM

(9) EVOLUTION THROUGH COMPUTER SIMULATED CHEMICAL KINETICS
    D. Segre et al., WEIZMANN INSTITUTE OF SCIENCE

(10) LIFE, BIOCHIRALITY & BROKEN SYMMETRIES
     J. van Klinken, UNIVERSITY OF GRONINGEN

(11) THE ABRUPT ORIGIN OF LIFE, OR HOW STABLE IS GENETIC MATERIAL?
     M. Levy &  S.L. Miller, UNIVERSITY OF CALIF SAN DIEGO

====================
(1) INTRODUCTION

From Paul Davies <pcwd@camtech.net.au>

The importance of impacts for the evolution of life on Earth has long
been recognized. Recently however, it has become clear that impacts
have played a key role in the origin of life too. First, the collision
of asteroids, comets and meteoroids with our planet delivered copious
quantities of organics, providing a rich veneer of life-encouraging
substances. More dramatically, the impact of large bodies would have
made life hazardous until the end of the epoch of heavy bombardment,
about 3.8 billion years ago. Indeed, as argued by Zahnle & Sleep, the
biggest impacts would have effectively sterilized the Earth’s surface
and sent a lethal heat pulse deep into the crust. Since there is fossil
evidence for life dating back to at least 3.5, and possibly 3.85
billion years ago, it seems as if life might have got going before the
heavy bombardment ceased.
 
One way of resolving this paradox is to suppose that early life survived
the bombardment by taking refuge either deep underground, or in orbit.
Microbes found kilometres under the ground and beneath the sea bed,
thriving in temperatures near or even above the normal boiling point of
water, suggest that life might have started hot and deep, or at least
cowered there, until the cosmic barrage abated. Genetic sequencing
reveals that these deep-living “hyperthermophiles” are the least
evolved of all organisms, and are, in effect, living fossils clinging
to an ancient lifestyle. By studying these bizarre microbes, we gain
insight into the conditions that prevailed on the primeval Earth,
nearly 4 billion years ago.
 
The same impacts that created such hostile surface conditions on Earth
would also have blasted huge quantities of material into space. Some of
the rocks ejected from Earth would have contained living microbes.
Cocooned within a rock, shielded from the lethal radiation in space,
and freeze-dried to –50C or more, many of these microbes would have
remained viable for thousands or even millions of years. It is
inevitable that some of them will have reached Mars, and possibly
beyond. Note that this theory differs from that of Hoyle and
Wickramasinghe, who have long advocated the propagation of microbes
over great distances within comets or, more controversially, by wafting
naked through space, exposed to radiation.
 
There is strong evidence that 3.5 billion years ago Mars was warm and
wet, and not unlike the Earth. It had volcanoes and rivers and possibly
a shallow ocean. Any terrestrial microbes that survived entry into the
martian atmosphere may well have found surface conditions there
congenial. For this reason, it is highly likely that there was life on
Mars at one time, even if it only transferred there from Earth.
 
More interesting is the possibility that life either began on Mars and
came to Earth by the foregoing mechanism, or emerged independently on
both planets. If terrestrial life started hot and deep, it may well
have been incubated close to the volcanic vents that are dotted along
the ocean floor. These so-called black smokers currently harbour rich
ecosystems of organisms. Significantly, the primary producers in the
black smoker life chains are the ancient hyperthermophiles.
 
Mars offers some advantages over Earth as a place for life to get
started. Being a smaller planet, it cooled quicker. The comfort zone of
organisms inhabiting the crust would have extended deeper sooner,
providing more secure refugia against impacts. Also, the impacts
themselves would have been fewer and less energetic than on Earth
because of the lower surface gravity. (See CCNet DIGEST, 2 December
1998.)
 
Given that material is continually exchanged between Earth and Mars, the
possibility of planetary cross-contamination by microbes riding inside
rocks is obvious. Nevertheless, when I first suggested the idea in the
early 1990s (Jay Melosh at the University of Arizona had independently
arrived at the same conclusion), it was greeted with widespread 
scepticism. Today, it has been accepted by NASA in its quarantine
policy for the Mars sample return mission.
 
Long ago, the traffic of impact ejecta between the two planets was much
more prolific. The consequences of interplanetary inoculation for the
origin and early evolution of life are far from clear. Did life go from
Earth to Mars or vice versa? Did life get going more than once? Might
we find an ancient side-branch of our tree of life lurking deep beneath
the surface of the Red Planet today? Can we imagine interplanetary
symbiosis, with terrestrial bacteria merging with martian microbes?
Could apparently extinct terrestrial microbes return to Earth inside
rocks ejected by ancient impacts?
 
Many important questions remain unanswered, but even if we do manage to
unravel the where and the when of life’s origin, the burning question of
how remains a tantalizing mystery. In spite of rapid progress in
pre-biotic chemistry, researchers are far from understanding how even
the simplest organism can arise from lifeless chemicals spontaneously.
Particularly troublesome is the origin of biological information, since
the genetic basis of life represents a large amount of very specific
information encoded on complex macromolecules. Merely generating
molecular complexity will not do; only information-based complexity
carries the secret of life. The subject of information theory is still
very much in its infancy, but it is clearly poised to make a
contribution to the riddle of biogenesis at least as significant as
that of organic chemistry.
 
In the bible, life is the fifth of the originating miracles (by my
counting). Although science is committed to discovering a natural origin
of life, to paraphrase Francis Crick, life seems to be almost a
miracle, so many are the special conditions it requires to get it
started. Unless we discover deep principles of nature that compel
matter and energy to self-organize into life, biology will seem like a
gigantic fluke, unique to Earth and perhaps, via rocky exchange, to its
near neighbours. If we do find life far beyond Earth, it will be
powerful evidence for bio-friendly universal laws that can generate
biological information from meaningless chaos. If so, then life will be
written into the logical structure of nature, and the philosophical
consequences would be profound indeed.

=================
(2) THE MOTHER OF ALL QUESTIONS

From NATURE, vol  395, 8 Oct 1998, p 560.
http://www.physics.adelaide.edu.au/itp/staff/pcwd/reviews/bengtson.html

The Fifth Miracle: The Search for the Origin of Life. By Paul Davies.
Allen Lane 1998 260pp 18.99
 
Stefan Bengtson
 
It may be that The Fifth Miracle is a misnomer, and the creation of
life was only the Third Miracle. (Biblical scholars told Paul Davies
that the creation of the Universe, as recounted in Genesis, wasn't
really a separate miracle, and shouldn't we just write off the
creation of dry land as a mere mopping-up act-leaving the creation of
light and of the firmament as the first two?) The three miracles
might then correspond to the classic subdivisions of science: physics,
chemistry and biology. That these are deeply entangled we already know.
If we can figure out in what way they are entangled, we will understand
something fundamental about life, the Universe and everything.

Davies's book is a small miracle in itself. In a little more than 200
pages he pursues the Mother of All Questions - "what is life?" - in a
way that should be deeply satisfying to physicists, chemists and
biologists alike, and he does this in a clear and potent style that
should make the book equally stimulating to non-scientists. (Whoever
says that you cannot write about science both simply and accurately
hasn't read Paul Davies.) A few slips-of-the-keyboard remind us that
the writer is not an expert in natural history (or Nordic lan-
guages), but this professed "simple-minded physicist" still
demonstrates a better grasp of the complexity and uniqueness of living
systems than most scientists, biologists included.

The cover shows Earth and Mars in close apposition. Too close, to be
exact, but this is to illustrate one of Davies's ideas, that Earth
and Mars are not quarantined and never have been. Rocks travel from
Mars to Earth (one of them killed a dog!) and probably in
the other direction too, and microorganisms thrive in rocks, as we have
lately become aware. Some rocks travel the distance in only a few
thousand years, so the possibility of cross-contamination with hardy
micro-organisms is considerable. This is fascinating in itself, but
whether or not it means that we are all Martians or that the Earth's
biosphere extends (or has extended) to the asteroid belt or beyond, it
makes the issue of life on other planets in the Solar System almost
trivial.

There is then the greater question, whether or not we are alone in the
Universe. Davies has little patience with those who take for granted
that as soon as there are Earth-like conditions, life will sprout. This
may be true, he says, but then we're making a gigantic assumption that
should not be taken lightly. To explore this assumption, he
takes the reader on an intellectual joyride up and down the entropy
slope, along the way pointing his sharp flashlight at often murky
concepts, such as order, organization, chance, randomness, specificity;
language and semantics.

The question of where the information content of life ultimately comes
from is, of course, not answered fully, but Davies speculates that
gravitation plays a crucial role by particularizing otherwise uniforrn
matter, and that the famous wave-particle duality of quantum mechanics
reflects a sofware-hardware entanglement built into the Universe
itself. Biological order may then be ascribed to emergent properties of
complex systems, with Darwinian selection serving to distil information
from the environment. Natural selection adds inforrnation by removing
possibilities.

Is life then also the final miracle? Hardly. Just as physics does not
fully explain chemistry and chemistry does not fully explain biology;
so life does not fully explain consciousness, and consciousness does
not fully explain human culture. Davies dwells only briefly on mind and
consciousness, but his book is a wonderful example of science as an
expression of human culture, and so truly belongs to the Fifth Miracle.
 
Stefan Bengtson is in the Department of Palaeozoology, Swedish Museum
of Natural History, Box 50007, SE-104 05 Stockholm, Sweden.
 
The US edition of The Fifth Miracle will be published by Simon &
Schuster in February.

=======================
(3) SEARCHING FOR LIFE ON JUPITER'S MOON EUROPA

From Andrew Yee <ayee@nova.astro.utoronto.ca>

Stanford University

CONTACT: David F. Salisbury, News Service
(650) 725-1944, e-mail: david.salisbury@stanford.edu

Searching For Life On Jupiter's Moon Europa

If the icy surface of Europa conceals a liquid ocean, which seems
increasingly likely, then the Jovian moon will become one of the
hottest spots in the solar system to look for alien life.

Europa Orbiter, a NASA mission in the early planning stages, that is
scheduled for launch in 2003, is being designed specifically to look
for evidence of a Europan ocean. If one is found, Europa and Earth
would be the only two worlds in the solar system where liquid water is
known to exist. And liquid water is thought to be essential for the
development of life.

Christopher Chyba -- the Carl Sagan Chair for the Study of Life in the
Universe at the SETI Institute and a consulting professor of geological
and environmental sciences at Stanford -- chairs the science definition
team for the mission. At the American Geophysical Union meeting in San
Francisco, he summarized the current evidence for an ocean on Europa
and described the instrument package that his team has proposed for the
next Europa mission.

Europa looks something like a cracked cue ball. The possibility that a
liquid water ocean may lurk beneath its ice crust was first raised at
the time of the Voyager missions in the late 1970s, but was reinforced
in 1996 when images of Europa's surface were beamed to Earth by the
Galileo spacecraft. The images showed areas where the surface ice has
been broken up and shifted around like pieces of a jigsaw puzzle,
leading Ronald Greeley from Arizona State University to propose that
the Europan icebergs must be lubricated from below by warm ice or
liquid water.

Since then, "there has been a convergence of evidence that supports the
existence of a liquid ocean on Europa," Chyba said.

* In addition to the iceberg-like areas, Galileo imagery has revealed
an impact crater that appears to have been filled in at the bottom,
areas that appear to show localized melting near the surface, and other
features consistent with a liquid layer below the ice;

* Galileo's onboard magnetometer, which measures magnetic fields, has
measured fluctuations that are consistent with the magnetic effects of
currents flowing in a salty ocean;

* Lack of cratering on Europa's surface indicates that it is very young
-- less than 10 million years -- which suggests that it is being
continually resurfaced, possibly by frost falling from liquid water
geysers encountering Europa's frigid surface temperatures, which hover
at -170 degrees Celsius;

* Theoretical estimates of the amount of heat produced by the
gravitational push and pull exerted on Europa by the other Jovian moons
indicate that it should be adequate to warm the moon's interior enough
to sustain a liquid ocean.

"All these lines of evidence point to a liquid water ocean," Chyba
said. The investigations that the science definition team has suggested
for the proposed $250 million Europa Orbiter include imaging,
altimetry, gravity measurements and subsurface radar soundings.

"The most decisive measurements are likely to come from the altimetry
and gravity measurements," Chyba said.

As Europa travels in a slightly eccentric orbit around Jupiter, tides
are raised, similar to the lunar tides on Earth. If the distant
satellite contains a deep ocean covered by the thin ice crust, then the
tidal movements should be fairly large, producing a 30-meter rise and
fall each 3.5 days. But if the moon is solid ice the deformation would
be only a meter or so. The altimeter and gravity measurements
independently would measure this effect.

These measurements should be definitive for the case of a global ocean,
but would be more difficult to interpret if the liquid layer takes the
form of a number of discontinuous seas, Chyba said.

In that case, a radar sounder might provide the needed data. Radar is
routinely used to sound ice on Earth. That is how Lake Vostok -- a body
of water about the size of Lake Ontario buried under 3,700 meters of
ice in Antarctica -- was discovered. A clean interface between water
and ice can be seen clearly in radar reflections. Depending on the
consistency of the Europan ice, a radar sounder should be capable of
penetrating somewhere between a kilometer and several kilometers into
the crust.

"Even if the radar sounder did not find clear evidence of liquid water,
it would still provide us with extremely valuable information about the
subsurface geological features," Chyba said.

Another possible instrument is an infrared spectrometer. Such a device
could provide information about the chemical composition of Europa's
surface, including the presence of organic molecules.

The decision on which instruments the orbiter will carry will be made
next year. The selection will be particularly difficult because the
spacecraft will have an extremely small payload of about 20 kilograms,
he said.

"If the orbiter confirms that Europa has a liquid ocean, then it will
become one of hottest places in the solar system, along with Mars, to
search for life. In this case there will be an entire program of
exploration, likely involving a series of spacecraft to Europa." But if
the Moon does not conceal such an ocean, then it will move down
significantly on the space agency's priority list, he said.


Related links:

Galileo Europa home page
http://www.jpl.nasa.gov/galileo/europa/

====================
(4) INTERSTELLAR GRAINS AS AMINO ACID FACTORIES & THE ORIGIN OF LIFE

W.H. Sorrell: Interstellar grains as amino acid factories and the
origin of life. ASTROPHYSICS AND SPACE SCIENCE, 1997, Vol.253, No.1,
pp.27-41

UNIVERSITY OF MISSOURI,DEPT PHYS & ASTRON,ST LOUIS,MO,63121

Some two decades ago, Hoyle and Wickramasinghe (1976) proposed that the
physical conditions inside dense molecular clouds favour the formation
of amino acids and complex organic polymers. There now exists both
astronomical and laboratory evidence supporting this idea. Recent
millimeter array observations have discovered the amino acid glycine
(NH2CH2COOH) in the gas phase of the dense star-forming cloud
Sagittarius B2. These observations would pose serious problems for
present-day theories of molecule formation in space because it is
unlikely that glycline can form by the gas-phase reaction schemes
normally considered for dense cloud chemistry. Several laboratory
experiments suggest a new paradigm in which amino acids and other large
organic molecules are chemically manufactured inside the bulk interior
of icy grain mantles photoprocessed by direct and scattered ultraviolet
starlight. Frequent chemical explosions of the processed mantles would
eject large fragments of organic dust into the ambient cloud. Large
dust fragments break up into smaller ones by sputtering and ultimately
by photodissociation of individual molecules. Hence, a sizeable column
density (N approximate to 10(10) - 10(15) cm(-2)) of amino acids would
be present in the gaseous medium as a consequence of balancing the rate
of supply from exploding mantles with the rate of molecule destruction.
Exploding mantles can therefore solve the longstanding molecule
desorption problem for interstellar dense cloud chemistry. A sizeable
fraction of the organic dust population can survive destruction and
seed primitive planetary systems throughout our galaxy with
prebiological organic molecules needed for proteins and nucleic acids
in living organisms. This possibility provides fresh grounds for a new
version of the old panspermia hypothesis first introduced by
Anaxagoras. It is shown that panspermia is more important than asteroid
and cometary organic depositions onto primitive Earth. Furthermore, no
appeal to Miller-Urey synthesis in a nonoxidizing atmosphere of
primitive Earth is then needed to seed terrestrial life.
Copyright 1998, Institute for Scientific Information Inc.

=========================================
(5) CARBONACEOUS MICROMETEORITES & THE ORIGIN OF LIFE

M. Maurette: Carbonaceous micrometeorites and the origin of life
ORIGINS OF LIFE AND EVOLUTION OF THE BIOSPHERE, 1998, Vol.28,
No.4-6, pp.385-412

CTR SPECTROMETRIE NUCL & SPECTROMETRIE MASSE,BATIMENT 104,F-
91405 ORSAY,FRANCE

Giant micrometeorites (sizes ranging from approximate to 50 to 500 mu
m), such as those that were first recovered from clean pre-industrial
Antarctic ices in December 1987, represent by far the dominant source
of extraterrestrial carbonaceous material accreted by the Earth's
surface, about 50 000 times the amount delivered by meteorites (sizes
greater than or equal to a few cm). They correspond to large
interplanetary dust particles that survived unexpectedly well their
hypervelocity impact with the Earth's atmosphere, contrary to
predictions of theoretical models of such impacts. They are related to
relatively rare groups of carbonaceous chondrites (approximate to 2% of
the meteorite falls) and not to the most abundant meteorites (ordinary
chondrites and differentiated micrometeorites). About 80% of them
appear to be highly unequilibrated fine-grained assemblages of mineral
grains, where an abundant carbonaceous component is closely associated
on a scale of less than or equal to 0.1 mu m to both hydrous and
anhydrous minerals, including potential catalysts. These observations
suggest that micrometeorites could have functioned as individual
microscopic chemical reactors to contribute to the synthesis of
prebiotic molecules on the early Earth, about 4 billions years ago. The
recent identification of some of their complex organics (amino acids
and polycyclic aromatic hydrocarbons), and the observation that they
behave as very efficient 'cosmochromatographs', further support this
'early carbonaceous micrometeorite' scenario. Future prospects include
identifying the host phases (probably ferrihydrite) of their complex
organics, evaluating their catalytic activity, and assessing whether
synergetic interactions between micrometeorites and favorable zones of
the early Earth (such as submarine hydrothermal vents) accelerated
and/or modified such synthesis. Copyright 1998, Institute for
Scientific Information Inc.

=========================
(6) THE BIOLOGICAL POTENTIAL OF MARS, THE EARLY EARTH & EUROPA

B.M. Jakosky*) & E.L. Shock: The biological potential of Mars, the
early Earth, and Europa. JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, 1998,
Vol.103, No.E8, pp.19359-19364

*) UNIVERSITY OF COLORADO, ATMOSPHER & SPACE PHYS LAB, CAMPUS BOX
   392, BOULDER, CO, 80309

The potential biomass that could have existed on Mars is constrained by
the total amount of energy available to construct it. From an inventory
of the available geochemical sources of energy, we estimate that from
the time of the onset of the visible geologic record 4 b.y. ago to the
present, as much as 20 g cm(-2) of biota could have been created. This
is the same amount that could have been constructed on the early Earth
in only 100 million years. This indicates that there likely was
sufficient energy available to support an origin of life on Mars but
not sufficient energy to create a ubiquitous and lush biosphere.
Similar calculations for Europa suggest that even less geochemical
energy would have been available there. Copyright 1998, Institute for
Scientific Information Inc.

======================
(7) ELECTROMAGNETIC ORIGIN OF LIFE
           
I. Jerman: Electromagnetic origin of life. ELECTRO- AND MAGNETOBIOLOGY,
1998, Vol.17, No.3, pp.401-413

INSTITUE OF BIOELECTROMAGNET & NEW BIOL, CELOVSKA 264, LJUBLJANA
1000,SLOVENIA

The solution to the great mystery of life lies in the understanding of
its beginning. If life is not a mere chemical phenomenon but also an
electromagnetic one, electromagnetic fields should have played an
important role in its birth. Contemporary scientific efforts to solve
the mystery of the origin of life concentrate on various possible
chemical paths. The most evolved hypotheses try to understand the
beginning of life in terms of self-organizing properties of matter
(i.e., molecules). Since organisms have very peculiar electromagnetic
properties, it is possible and also probable that the origin of life
was based on cooperation between dipolar organic molecules and special
electromagnetic fields. In contrast to the prevalent hypotheses of
molecular self-organization, a testable hypothesis of self organization
of electromagnetic field-and-matter is presented. Copyright 1998,
Institute for Scientific Information Inc.

==================
(8) WHAT EXACTLY IS LIFE?

P.L. Luisi: About various definitions of life. ORIGINS OF LIFE AND
EVOLUTION OF THE BIOSPHERE, 1998, Vol.28, No.4-6, pp.613-622

ETH ZENTRUM,INST POLYMERE,CH-8092 ZURICH,SWITZERLAND

The old question of a definition of minimal life is taken up again at
the aim of providing a forum for an updated discussion. Briefly
discussed are the reasons why such an attempt has previously
encountered scepticism, and why such an attempt should be renewed at
this stage of the inquiry on the origin of life. Then some of the
definitions of life presently used are cited and briefly discussed,
starling with the definition adopted by NASA as a general working
definition. It is shown that this is too limited if one wishes to
provide a broad encompassing definition, and some extensions of it are
presented and discussed. Finally it is shown how the different
definitions of life reflect the main schools of thought that
presently dominate the field on the origin of life. Copyright 1998,
Institute for Scientific Information Inc.

============================= 
(9) SELF-REPLICATING ASYMMETRICAL FROZEN PROBABILITY

M.L. Glassman & A. Hochberg: The origin of life: self-replicating
asymmetrical frozen probability. MEDICAL HYPOTHESES, 1998, Vol.50,
No.1, pp.81-83

HEBREW UNIVERSITY JERUSALEM, INST LIFE SCI,DEPT BIOL CHEM,IL-91904
JERUSALEM, ISRAEL

Within each of us, as within each living or extinct creature, is a
broad piece from the story of life and creation. Both the evolution of
the universe-and the emergence df life on Earth can be considered as
being the result of critical events, such as phase transitions, that
occur with a certain probability and are characterized by a sudden
breakage of prior symmetry. These in turn result in self-perpetuating
conditions that are responsible for what we know and perceive today.
Copyright 1998, Institute for Scientific Information Inc.

==============
(10) EVOLUTION THROUGH COMPUTER SIMULATED CHEMICAL KINETICS

D. Segre, Y. Pilpel, D. Lancet: Mutual catalysis in sets of prebiotic
organic molecules: Evolution through computer simulated chemical
kinetics. PHYSICA A, 1998, Vol.249, No.1-4, pp.558-564

WEIZMANN INSTITUTE OF SCIENCE, DEPT MEMBRANE RES & BIOPHYS, IL-76100
REHOVOT, ISRAEL

A thorough outlook on the origin of life needs to delineate a
chemically rigorous, self-consistent path from highly heterogeneous,
random ensembles of relatively simple organic molecules, to an entity
that has rudimentary life-like characteristics. Such entity should be 
endowed with a capacity to express variation, undergo mutation-like
changes and manifest a simple evolutionary process. For simulating such
system we developed the Graded Autocatalysis Replication Domain (GARD)
model for explicit kinetic analysis of mutual catalysis in sets of
random oligomers derived from energized precursor monomers. The kinetic
properties of the GARD model are based on vesicle enclosure and
expansion. With the additional assumption of spontaneous vesicle
splitting, a GARD evolution scenario is envisaged as a consequence of
pure chemical kinetics. Here we show how the GARD model can serve as a
platform for investigating the dynamics of self-organization mechanisms
in molecular evolutionary processes. (C) 1998 Elsevier Science B.V. All
rights reserved.

=====================
(11) LIFE, BIOCHIRALITY & BROKEN SYMMETRIES

J. van Klinken: Broken symmetries at the origin of matter, at the
origin of life and at the origin of culture. ACTA PHYSICA POLONICA B,
1998, Vol.29, No.1-2, pp.11-23

UNIVERSITY OF GRONINGEN,KERNFYS VERSNELLER INST,NL-9747 AA
GRONINGEN,NETHERLANDS

In earliest cosmic history the universe started with matter and not
with antimatter. Shortly after the beginning the electroweak
interaction prominent in nuclear beta decay - acted as a lefthander.
Much later, in prebiotic evolution, optically left-handed amino acids
determined the unique signature of following terrestrial organic life.
Again aeons later, homo sapiens appears as predominantly right handed
and creates cultures with many broken symmetries. Along these pathways
of history it was essential that choices were made - left or right,
matter or antimatter but on several instances it seemed less relevant
which choices were made. We think that biochirality occurred by global
chance; perhaps by local necessity, but without causal links to the PCT
theorem. In other cases - e.g. the standardization to right-handed
screws - the choice will have been made by causal necessity.
Copyright 1998, Institute for Scientific Information Inc.

====================
(12) THE ABRUPT ORIGIN OF LIFE, OR HOW STABLE IS GENETIC MATERIAL?

M. Levy, S.L. Miller: The stability of the RNA bases: Implications for
the origin of life. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF
THE UNITED STATES OF AMERICA, 1998, Vol.95, No.14, pp.7933-7938

UNIVERSITY OF CALIF SAN DIEGO,DEPT CHEM & BIOCHEM,LA JOLLA,CA,92093

High-temperature origin-of-life theories require that the components of
the first genetic material are stable. We therefore have measured the
half-lives for the decomposition of the nucleobases. They have been
found to be short on the geologic time scale. At 100 degrees C, the
growth temperatures of the hyperthermophiles, the half-lives are too
short to allow for the adequate accumulation of these compounds (t(1/2)
for A and G approximate to 1 yr; U = 12 yr; C = 19 days). Therefore,
unless the origin of life took place extremely rapidly (<100 yr), we
conclude that a high-temperature origin of life may be possible, but it
cannot involve adenine, uracil, guanine, or cytosine, The rates of
hydrolysis at 100 degrees C also suggest that an ocean-boiling asteroid
impact would reset the prebiotic clock, requiring prebiotic synthetic
processes to begin again, At 0 degrees C, A, U, G, and T appear to be
sufficiently stable (t(1/2) greater than or equal to 10(6) yr) to be
involved in a low-temperature origin of life. However, the lack of
stability of cytosine at 0 degrees C (t(1/2) = 17,000 yr) raises the
possibility that the GC base pair may not have been used in the
first genetic material unless life arose quickly (<10(6) yr) after a
sterilization event. A two-letter code or an alternative base pair may
have been used instead. Copyright 1998, Institute for Scientific
Information Inc.

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