This chapter is not published in the current edition of Nature's Holism.
"Assuming any kind of hypercyclic organization as a first step having come into existence spontaneously, some prerequisites are necessary from thermodynamics of irreversible processes: large concentration gradients of certain substances and high affinities of their reactions catalyzed at surfaces; small semipermeable compartments due to the related diffusion coefficients and large reservoirs of substrates and for products." ( Krueger & Kissel, 1989)
"Submarine hydrothermal vents are the only contemporary geological environment which may be called truly primeval; they continue to be a major source of gases and dissolved elements to the modern ocean as they were to the Archean ocean." (Baross & Hoffman, 1985)
"Webs and chains of historical events are so intricate, so imbued with random and chaotic elements, so unrepeatable in encompassing such a multitude of unique (and uniquely interacting) objects, that standard models of simple prediction and replication do not apply." . . . "History includes too much chaos, or extremely sensitive dependence on minute and unmeasurable differences in initial conditions, leading to massively divergent outcomes based on tiny and unknowable disparities in starting points." (Gould, 1994)
ORIGIN OF LIFE (Biogenesis)?
This book has to conclude with a view on the origins of the holistic process and the origins of life.
|
NUMBER OF ITERATIONS:
|
5000
|
 |
|
START NUMBER FOR SPECIES:
|
10000
|
|
|
r FOR SPECIES A:
|
8
|
|
|
r FOR SPECIES B:
|
3.8
|
|
|
r FOR SPECIES C:
|
4
|
|
|
k of A & B & C:
|
1000000
|
|
|
m FOR SPECIES C:
|
2
|
|
|
m FOR SPECIES A:
|
2
|
|
|
m FOR SPECIES B:
|
2
|
|
|
i B-C: effect of C on B.
|
0.8
|
|
|
i A-C: effect of C on A.
|
1.1
|
|
|
i C-B: effect of B on C.
|
1.1
|
|
|
i C-A: effect of A on C.
|
0.5
|
|
|
i B-A: effect of A on B.
|
1.1
|
|
|
i A-B: effect of B on A.
|
0.5
|
There are interactions that can attain stability, but for which I
cannot find a parallel in nature. In the above interaction of three
associated
"species", each interaction is beneficial to the one "partner" and
costly
to the other. The three species form an interactive triangle, where the
one link from each species is beneficial and the other is costly in
terms
of energy exchange. The beauty of this model is its stability.
Stable,
complex chemical associations are the key to biogenesis (the origin of
life)
and an array of chemical compounds needs to be investigated, to see
which
are likely precursors.
This "complexity model" hints at a form of stability that could have
occurred, via the holistic process, at life's very origins. This view
perceives
life as having multi-planetary origins and not having existed forever
or
arriving from outer space as suggested by Davies in his book "The Fifth
Miracle" (1999). Davies' view requires a steady-state cosmology, with
no
origins. However, a religious perspective teaches us that Creation has
a
beginning, so our universe is not eternal.
The system of interactions illustrated above, forms a self-reinforcing
reaction loop. Davies (1999) terms this a hypercycle. Just as
oxygen was an addition to our atmosphere, created by life, it in turn
transforming the constitution of life and possible life forms, so the
early environment may have been radically changed once the first
hypercycles were triggered. For the persistence of life forms such as
us, these changes to our environment are necessarily irreversible. The
early earth’s ocean environment, before the origin of life, would have
been composed of a rich broth of potentially volatile constituents. At
some critical concentration in this system, similar to the formation of
sugar crystals on a string in a supersaturated solution, various
reactions would have started in a type of cascade effect within
this complex chemical broth. Volcanic action and the impact of massive
comets
and meteorites, in this early era of the earth’s formation, would have
ensured that this solution received both massive inputs of chemicals,
such as “organic” carbon, sulphur and nitrogen and the stimulus of heat
(see the July 1999
Scientific American Issue by Bernstein
et al.). In the first 700 thousand years of the earth’s formation, the
crust would have been made of thin protoplates easily churned up by a
molten lava interior that was hotter than today.
The earth is aged at somewhere beyond 4.6 billion years. Some lunar
meteorite craters are dated at over four billion years (Davies, 1999).
A
very intense period of bombardment occurred between 4 billion and 3.8
billion
years ago. Life emerged soon after this, with current earliest
estimates
at between 3,5 and 3.85 billion years ago. Carbon-isotopes from
carbonaceous
inclusions within grains of apatite (basic calcium phosphate) from
3,800-Myr-old
banded iron formations from the Isua supracrustal belt, West Greenland
(and
a slightly older formation from the nearby Akilia island), are
isotopically
light, suggestive of biological activity (Mojzsis et al, 1996),
(Bernstein,
et al., 1999). The oldest stromatolites, an already very complex
organism,
are around 3.5 billion years old. The narrow gap between the two events
may
be no coincidence. The great leap between non-life-chemistry
and
a perpetuating entity had to occur within a period of 3.5 and 4 billion
years
ago. During this intense period of bombardment, any part of the earth
was
impacted at least once in 350 years (Gore & Sugar, 1985). The
result
of this intense meteorite and comet bombardment and the action of plate
tectonics,
is that it is difficult to find rocks older than 3.8 billion years.
Some
small crystals called zircons have been dated at 4.2 billion years old
(Gore
& Sugar, 1985). Ancient sedimentary rocks from South Africa, of
between
3.2 and 3.4 billion years old, already possessed bacteria-like
microfossils
of significant complexity (Dickerson, 1978).
In the early oceans, saturated with the chemicals from these early processes and warmed by the lava of the young earth and sunlight, a few self-reinforcing and hence stable hypercycles could have easily formed. Similar to the principle of the creation of matter in the universe from a uniform entropic system, so this rich broth, with stable hypercycles, would have generated more complex compounds. Part of the “fuel” for this process was the continual addition of water, atmospheric gases, amphiphilic molecules and organic matter (such as methane, ethane and polycyclic aromatic hydrocarbons), from comets, meteorites and interplanetary dust particles. Meteorites, although mostly rock and metals, contain unusual compounds such as nucleobases , ketones , quinones , carboxylic acids , amines and amides . To date eight of the 20 essential amino acids that form the proteins of life have been found in meteorites (Bernstein, et al., 1999). Increased structural complexity in the oceans, in turn increases the potential chemical interactions, so increasing the potential for more complex hypercycles.
Each phase is sequentially dependent upon the previous phase and the process is irreversible. Chemical hypercycles, stable and self-perpetuating, establish the first holistic principle – perpetuity. Under the influence of light energy, even with the high levels of UV radiation, solar-triggered hypercycles cold have ‘evolved’ very early, so that the first life or perhaps proto-life forms used light energy. This hypothesis is necessary to explain the early evolution of photosynthesis. Captured in chemical structure as a potential energy, solar energy could have triggered and perpetuated early hypercycles and opened the door to the utilisation of inert compounds from the environment. The Astrochemistry Laboratory in the Space Sciences Division at NASA's Ames Research Center specializes in the study of extraterrestrial materials. They have found many different organic molecules that originate in space. Quinone molecules formed in space have a structure "nearly identical" to those used by chlorophyll molecules in transferring light energy from one part of a plant cell to another. Quinones are also able to absorb ultraviolet radiation, so may have served as a UV shield and light energy trap for early life forms.
Other origin-of-life-theorists speculate that life first evolved alongside deep ocean volvanic vents ( "smokers"). Here, with pressures of at least 500 atmospheres and temperatures of 300 to 500C, reactions can take place between oxides of carbon and nitrogen in a reducing aqueous environment producing compounds that are found in the citric acid cycle. These researchers believe that the reductive citric acid cycle, as biochemistry's basic thermodynamic engine, was the first chemical process of life. These vents provide environmental stability through millions and even billions of years and provide a source of the compounds needed to get life started. The chemical processes of the reductive citric acid cycle provides amino acids through animation reactions, sugars through pyruvate and lipids through thioacetate or some sort of sulfur-acetyl compounds (Wills, 1997).
Another clue and hint to early life processes is the existence of the triplet codon as part of our genetic structure. This particular triplet association may give a clue to the earliest triplet hypercycles that existed in the early oceans. Its presence needs to be investigated, to see how it evolved.
Hypothetically, the earliest life form would have comprised of some sort of triplet hypercycle that absorbed light energy and utilised compounds from its environment in the perpetuation of the hypercycle. No membranes were needed to maintain the hypercycles. An important point is that this process may have been largely irreversible, leading to greater complexity, with no possibility of a return to the earlier condition. At some point, two or more hypercycles become dependent upon one another’s by-products and so interdependent hypercycles evolved. This is the first stage in the evolution of compatibility. Driven by solar energy, and extraterrestrial sources of organic compounds, complexity increases. However, knowledge of the exact moment when chemistry becomes life still remains within the realm of the divine.
Setting the stage:
We need to understand as much as possible about the
conditions under which life first evolved. At the formation of the
oceans, the Earth's crust was cooling and reacting with
volatile or highly reactive gases of an acidic, reducing nature
to produce the oceans and an initial sedimentary rock mass. Some degree
of stability and perhaps reduction in temperature
is required in this aspect of the earth's formation for life to evolve.
The
first life forms may have been extreme thermophiles (heat loving), but
there
is still some upper limit. These volatile gases formed an atmosphere of
water, carbon gases (carbon dioxide, methane, carbon monoxide), sulphur
gases (hydrogen sulphide), halogen compounds (hydrochloric acid) and
nitrogenous compounds (ammonia in the oceans and nitrogen gas in the
air), along with minor amounts of other gases. As the atmosphere
(containing water vapour, carbon dioxide, and hydrochloric acid in the
ratio of 20:3:1) cooled from about 600º C, the water vapour
condensed into an early hot ocean. Hydrochloric acid
in the ocean (about 1 mole per litre) would react vigorously with
crustal
surface minerals, creating a residue of aluminous clay minerals through
the
dissolution of silica and cations. This clay formed the sediments of
the
early ocean basins.
Between 4 and 2.5 Billion years ago (refer
to geological table ) volcanic activity was so intense that larger
continents could not form. Life only established when a semblance
of stability prevailed! Volcanic
activity, released gases, oxidising iron and removing oxygen from the
atmosphere.
An unusually beautiful world this must have been. Without oxygen, the
sky
would have been pink and the oceans brown (Sepkosli, 1993), but without
human eyes, there was no creature to appreciate this beauty! Lifeless
continents
would break up and change continually, subject to incredible volcanic
forces.
By two billion years ago (200 pages), much radioactivity had diminished
and the world had cooled considerably. With no atmospheric oxygen,
many organic compounds that would rapidly break down in our current
atmosphere
were stable in the "original" atmosphere (Dickerson, 1978). Without an
ozone
layer made from oxygen, ultraviolet light easily reached the earth's
surface,
providing an energy source for the conversion of molecules such as
carbon
dioxide, water and ammonia into "organic" compounds. Analysis of
organic
matter in carbonaceous chondrites reveals three types or
fractions.
One component is identified as of interstellar origin. The other two
fractions
were probably synthesized on earth. The second, the polar organics
(i.e.
amino acids), were probably formed from hydrocarbons and ammonium
carbonate
in a liquid water environment. The third could have originated in
iron-rich
clays (Hartman, 1993). Another fairly obvious constraint is that the
earth's
surface temperature would have limited microbial evolution in
the
Precambrian (Schwartzman, 1995). Other primary physical factors
important
to life's evolution on earth include pressure and radiation
regimes.
Temperature and pressure regulate the presence and duration of liquid
water
on the surface (Mancinelli & Banin, 1995). The early atmosphere was
rich in CO 2, creating a greenhouse effect. This
carbon dioxide
could have caused a dense 10-bar pressure in the early atmosphere
(Chyba,
1991). Photosynthetic organisms evolved within this climate and then
proceeded
to remove CO 2 from the atmosphere, causing the Earth to
cool
and influencing the formation of the carbonate sedimentary deposits
found
as a large part of the Earth's crust (biota significantly enhance
weathering
rates & erosion) (Schwartzman, 1991).
Ice Ages Rock the Cradle:
Although life emerged between 3,5 and 3.85 billion years ago, two
episodes of massive and extensive glaciation of the
earth occurred, holding back the process of diversification and
formation of complex animals for nearly 3 billion years! One extensive
glaciation period
occurred less than a billion years ago during the Neoproterozoic Era,
and
another during the Paleoproterozoic Era 2.2 billion years ago
(Leutwyler, 1999). By measuring the magnetic directions of ancient rock
specimens from sites such as in South Africa, researchers were able to
compute the direction and distance to the ancient north and south
poles. These samples, 11 degrees (plus or minus five degrees) from the
equator, when Earth was 2.4 billion years old, show evidence of glacial
deposits. Other features of these Neoproterozoic oceans that form a
complex picture of events from this period are:
[i] Mixed with the glacial debris are unusual deposits of iron-rich
rock, requiring an atmosphere with little or no oxygen for their
formation, yet oxygen was present in the atmosphere.
[ii] Rocks that form in warm water were deposited soon after the
glaciers receded.
[iii] As ice and snow's albedo effect
tend to reflect sunlight much better than land and water, it is
difficult to understand how the Earth reheated and emerged from such an
extensive
ice age.
[iv] Carbon isotopic signatures in the rocks of this period indicate a
prolonged drop in biological productivity, reflecting a decreased
biodiversity
during the ice age.
[v] Carbonate rocks dominated by calcium- and magnesium-carbonate
minerals lie just above the Neoproterozoic glacial debris of the
period.
[vi] These massive glaciations occurred just before the rapid
diversification of multicellular life - the Cambrian explosion -
between 575 and 525 million years ago. No massive glaciation cycle was
repeated after this period.
The combination of these events is explained through periods of global glaciation that reached the equator, covering the earth in ice, freezing out most of the habitats available to life. At this time (the Neoproterozoic), the continents were clustered together near the equator. Before volcanic larva of the time hardened, tiny mineral grains aligned themselves with the magnetic field, dipping slightly relative to horizontal because of their position near the equator. The first massive glaciation ('snowball Earth') followed the emergence of photosynthetic life, when oxygen levels in the atmosphere began to rise. Prior to this, methane, carbon dioxide and water vapour were major greenhouse gases in the atmosphere. Living, photosynthesising animals removed carbon dioxide and produced oxygen, a "new" gas for this primitive atmosphere. Only one-hundredth of a percent of today's atmospheric oxygen is enough to deplete the methane, so the earth started cooling as greenhouse gases disappeared. Slowly the ice spread eventually reaching latitudes lower than around 30 degrees north or south of the equator. This would cause the planet's albedo to rise at a faster rate, with sunlight striking a larger surface area of ice per degree of latitude, causing the massive glaciation. The massive glaciation that followed pushed all life to a few isolated pockets and natural productivity diminished. Natural volcanic activity would take another 5 to 10 million years to generate enough carbon dioxide (350 times the present-day concentration of carbon dioxide) to melt the glaciers. With relatively low levels of photosynthetic organisms, carbon dioxide again built up as a greenhouse gas, trapping the sun's heat and warming the earth.
Four such glaciations developed between 750 million and 580 million years ago: photosynthetic organisms flourished, depleted carbon dioxide, caused the earth to cool, started a massive global glaciation that in turn reduced all life to small pockets and carbon dioxide levels, produced by volcanic activity, rose again, warming the earth and ended the glaciation. In each case, the earth recovered from these ice ages, through a complex process leading to increased carbon dioxide, the main greenhouse gas. Volcanic eruptions, no more frequent than today's would have released a lot of carbon dioxide into the atmosphere during the ice ages. Normally the natural erosion of silicate rocks precipitates the carbon. Through the chemical breakdown of the rocks, carbon dioxide is converted to bicarbonate and washed to the oceans. This bicarbonate then reacts with calcium and magnesium ions to produce carbonate sediments. This process is halted during a massive glaciation, as rock erosion cannot occur, with the land buried under hundreds of metres of ice! With the onset of this massive glaciation, carbon dioxide released from volcanoes accumulated in the atmosphere.
Ice covered oceans were probably devoid of oxygen. At these ice covers melted, the iron (expelled from seafloor hot springs) that had accumulated in the water would be oxidised and precipitated through the presence of atmospheric and photosynthetic oxygen. Once the melting process began, the high-albedo ice quickly disappeared, while greenhouse atmosphere helped to drive surface temperatures upward to perhaps 50 degrees C, causing a very rapid reversal. Under these conditions of high carbonates, iron and carbon dioxide, photosynthetic activity must have been very intense. The water cycle, patterns of erosion and atmospheric water vapour levels would have all pushed this process of departure from the massive ice age. The reversal appears to have been rapid - possibly in only a few thousand years duration. Carbon in carbonate rocks, formed in life-filled oceans, has a higher ratio of carbon 13 to carbon 12 than does the carbon from a volcano. Carbon dioxide from volcanoes is about 1 percent carbon 13. Measurements of these ratios shows that life only recovered to current levels of productivity after the carbonates were precipitated (Hoffman & Schrag, 2000).
The eukaryotes that emerged from this Neoproterozoic calamity then entered a phase of rapid diversification known as the Cambrian explosion. All 11 animal phyla present today emerged rapidly after the last massive glaciation. It seems plausible that the Cambrian explosion of diversification became possible when the earth ended the grip of a phase of massive glaciations that have not since been repeated.
In addition to book references are the following web references:
- Caltech Scientists Find Evidence For Massive Ice Age When Earth Was 2.4 billion Years Old - http://broccoli.caltech.edu/~media/Press_Releases/PR11789.html
- Albedo: http://zebu.uoregon.edu/~js/glossary/albedo.html
- The First Ice Age: http://www.sciam.com/explorations/1999/110199ice/index.html
- EVOLUTION OF A SNOWBALL EARTH EVENT...AND ITS HOTHOUSE AFTERMATH: http://www.sciam.com/2000/0100issue/0100hoffmanbox1.html
- Snowball Earth http://www.sciam.com/2000/0100issue/0100hoffman.html
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