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 Earths
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 lifes 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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