juliana

or even whether other entities endowed with intellectual capacities will be
created. It is hard to imagine bearing in mind the long way up to here
presented by T. Nikolov (1994) in the following statement: “Science by now
has registered about 2.5 million species of animals and plants, and most
probably living things on the our planet amount to 10 million species. It is
assumed that the entire history of life on the Earth would record a number
of about 4.5 billion species of animals and plants”.
Data from paleontological findings (Table 5) show that cell structures
have existed more than 3.4 billion years. The process of their formation
however remains unclear. This imposes the necessity for a better
development of “molecular paleontology” and serious studies on the
“molecular fossils” as is the justified insistence of Calvin (1971) and Rutten
(1973). Only then it can be exactly established when chemical evolution
has transitioned to biological.

Are We Alone in the Universe?

Section 1.8. Different concepts have been created by man for the Universe
— religious, philosophical, astronomical, physical, chemical
etc. In our case it is conceived as a space in which matter exists and
evolves in time, and from that matter life has emerged under definite
conditions as a result.
Modern scientific knowledge recognizes the fact that there are no
less than two hundred billion galaxies in the Universe incorporating a
total of about 10²¹ stars. The Metagalaxy which has formed the Milky
Way (Greek: galactikós — milky) that is observed in the sky and which
we call “our Galaxy” contains about 30 galaxies with more than one
hundred billion stars (10¹¹). In the Solar system, except the Earth, 8
other planets are found with 34 “Moons” moving in along established
orbits.
According to the model of A. Friedmann the Universe is constantly
inflatiing and its age is roughly 16—20 billion years. It is not clear however
whether this inflation pertains to its expansion in space or to the
development the Metagalaxy mentioned above. As to its age it is hard to
accept that the Universe may have a “birthday” since this contradicts the
notion of its eternity and infinity.
In Rozental’s opinion (Rozental, 1989) Friedmann’s model ought to
be applied only to Metagalaxies and not the Universe as a whole.
Rozental has underlined the difference between metagalactic time ™
and the time for the development of the entire Universe (tu), since tm is
limited and tu — limitless.
Alongside the problem of the origin and evolution of life on Earth, still
another great question has troubled mankind and it can be posed like
this: are we alone in the Universe? The answer to this question is one

microfossils from Bulawayo Region (South Rhodesia) and the Transvaal Series
(South Africa). Their age was determined to be in the limits of 2.8—2.2 bln.
years.
The problem of whether prior to the period of the late archaic epoch
photosynthesis has occurred with the release of molecular oxygen or via
the mechanisms of methanogenesis, glycolysis or other routes of nitrogen
fixation without the release of oxygen remains unsolved.
The Gunflint Formation (southern part of Ontario, Canada and the
northern part of Minnesota, USA) gives a clue to the disclosure of the
“secrets” of the increased diversity of living organisms existing 2 billion
years ago. Except the bacteria and algae mentioned up to here,
ferrobacteria, multicellular thread-like structures, lower forms of fungi and
radial colonies are found in this formation.
A significant progress in the evolution of life has been registered in the
findings from the remains in the Beck Spring Formation (Eastern California)
aged 1.4—1.2 bln. years. Alongside the prokaryotes (bacteria and blue-green
algae) eukaryotes have also found (thread-like blue-green algae,
plankton green and yellow-brown algae). The presence of minimal
quantities of molecular oxygen (O₂) is also recorded which is conceived as
resulting from the then existing photosynthesizing organisms.
Following its natural course, evolution of life has arisen to new higher
forms of organization. The imprints of living organisms found in the formations
Bitter Springs (Central Australia) and the Grand Canyon of the Colorado River
(Arizona) testify to this development. These fossils show that in the Later
Riphean (1—0.9 bln. years) a transition from a haploid to a diploid form of
existence has taken place. Except the amitotic division cells in mitosis as well
as in meiosis (characteristic of the reduction division in sexual cells) were
observed. Sexual reproduction in eukaryotes has emerged.
The arising of the sexual process as a biological phenomenon marks
a new stage in the evolution of life. The mechanisms for exchange of
genetic material have become more diversified and the possibilities for
the creation of new forms as a result of genetic recombinations have
grown considerably. In the Early Cambrium (0.7—0.6 bln. years) higher
forms of life appear on the scene — multicellular algae, leaf-like and fern-like
stems, jelly-fish, coral-like organisms, worms and askeletal animals
(Metazoa). Well-preserved remains of such creatures have been found in
the Ediacara Region (Southern Australia), in the Russian and Siberian
Platforms, etc.
Let us stop up to here our “excursion” along the trail of life on Earth.
The “silhouette” of the cell and its evolution that have led to the stunning
diversity of living organisms is reflected on the background of a period of
approximately 3.8 bln. years. It is not the subject of this book to
contemplate on what future course evolution will take or what new forms
will emerge, in what direction the thus created Homo sapiens will develop

image

Figure 1–10. Distribution of microfossils in carbonaceous laminae of the 
Swartkoppie Formation, South Africa (a). Arrows designate discernible 
individuals; (b—e) — stages in cell division; (f, k) — dyads; (g—j) 
Aphanocapsa sp., illustrating binary cell division in modern prokaryotes. 
Bar 10 μm (After Knoll, Barghoorn, 1977).

The Swaziland system in South Africa is a remarkable earth formation. It is
17 km deep and is divided into three groups: upper — Fig Tree (2150 m); lower
— Onverwacht (15 200 m) and the adjoining to them Moodies (3000 m). Its age
determined after the rubidium-stroncium method amounts to 3.4—3.1 bln. years.
Photosynthesizing bacteria and cyanobacteria are discovered also in

other authors (Moorbath et al., 1973; Bridgwater et al., 1981) who would rather
assume these as inorganic structures or some unclear inclusions.

In the layers of the formations from the Warrawoona and Pilbara Groops
(West Australia) and Mushandike (Zimbabwe) aged 3.5 bln. years no imprints
of living forms have been detected. Only biogenic structures in stromatolytes
with an increased isotope ratio of ¹²C/¹³C have been found.
As most ancient authentic fossil microorganisms are considered the
findings from the Fig Tree Group in Swaziland, South Africa (see Table 5).
Well-preserved unicellular organisms defined as bacteria and blue-green
algae are well visible in the photographs (Fig. 1–10). Their more typical
representatives are Eubacterium isolatum (0.7 μm long) and
Archaeosphaeroides barbertonensis (17—20 μm in diameter). According to
the authors (Knoll and Barghoorn, 1977) a process of division is observed
in some of them. In the opinion of Schopf (1976) these spheric formations
are not bacteria but remains of prebiotic microsphere-like structures, similar
to those spontaneously formed upon mixing inorganic compounds in
laboratory conditions. The data, however, are more in favour of the
conception that living organisms have arisen prior to the Swaziland system.

Tracing Life on the Earth

Section 1.7. The hypothesis of the earth origin of life seems more
plausible. The reasons for that conclusion are quite a few.
Three of them are however most worth mentioning:

1. A combination of favourable factors such as temperature, primeval
   atmosphere, availability of water in a liquid state, optimal solar
   radiation, etc.
2. Evolution of metabolism in direct dependence on the development
   of lithosphere, hydrosphere and atmosphere of the Earth with a
   strongly expressed demarcation line between the anaerobic and
   aerobic ways of existence of the living organisms marked by the
   absence and later presence of molecular oxygen (O₂).
3. Traces left by the living organisms in earth layers.
   A satisfactory scientific hypothesis of the origin, formation and
   development of our planet and the living systems emerged on it has been
   created on the basis of numerous studies in the different fields of science. The
   age of Earth is defined to 5—6 billions of years. Biochemical evolution has
   started after the formation of the earth mantle i.e. about 4.5 billion years ago,
   the prerequisites for its emergence being prepared at the still earlier space
   stage of chemical evolution. The remains of the most ancient known and
   preserved fossils of life forms are dated back to 3.5—3.8 billion years which
   indicates that for the formation of the first cell structures about 1 billion years
   and according to some authors even more, have been necessary.
   The chronology of the individual stages of the historical development of
   the Earth is given in Table 4. Supplementing it, Ernst (1983) divide the
   Archean Era (4.55—2.5 bln. years) into three main periods: Hadean,
   encompassing the initial period after the formation of the Earth (4.55—3.9 bln.
   years); Early Archean (3.9—2.9 bln. years) and Late Archean (2.9—2.5 bln.years).
   
   The road, which the researchers must follow in the search of life is
   difficult. But the endeavour has already been undertaken and without any
   doubt it will be brought to an end and sufficiently resolved. Two are the
   main obstacles for the elucidation of that problem.
   
   First. The strong metamorphism of rock formations and sediments
   which has to a great extent wiped out the traces of the primary living
   systems that have existed prior to the formation of cell organisms.
   
   Second. The impossibility to differentiate abiogenic organic matter
   from the biogenic one. This also hampers exobiologists in finding
   convincing proofs of the extraterrestrial origin of biomatter.
   The earliest imprints of living organisms (fossils) are the reported findings
   from the Isua Formation (West Greenland) aged approximately 3.8 bln. years
   (see Table 5). The authors themselves (Pflug, 1978; Pflug, Jaeschke-Boyer,
   1979) have expressed doubts that the Isuasfera named by them are
   organisms resembling modern yeasts. The same doubts were expressed by

oxidation — carbohydrates, fatty acids, amino acids, etc. Their degradation
can follow different pathways — glycolysis, the pentosophosphate cycle,
the Krebs cycle known as the cycle of tricarboxylic acids (Fig. 1–9) or in the
respiratory chains, but always accompanied with the formation of CO₂ and
H₂O as end products. The energy released is used for the synthesis of
ATP. These problems are a subject of any textbook in biochemistry and
that is why will be omitted.

image

Figure 1–9. Cycle of tricarboxylic acids (Krebs cycle)

was mainly due to CO₂ and N₂, actively participating in the metabolic
processes.
Carbon remains the most “mysterious” element. It forms stable bonds
and chains of various configurations, different sizes and functional groups.
The availability of four electrons in its outer envelope is the prerequisite for
the formation of four covalent bonds with the atoms of other elements as
well as with its own

The bonds of carbon atom with hydrogen ones are very stable. From
a biological point of view especially important are the peptide bonds

which lead to the formation of long polypeptide chains

resulting from the release of H₂O from the carboxyl group of one of the amino
acids and the amino group of the other one (see Figs. 2–31 and 2–52). The
combination of these four organic elements and the linkage of amino acids in
polypeptides with the release of water can be regarded as the beginning of the
origin of life supplied with simpler mechanisms of self-reproduction without the
participation of nucleic acids.
A serious “candidate” for the place and the role of carbon in the build-up
of living entities could be silicon (Si). It ranks second in content in the
lithosphere (21.2%) right after oxygen. It also has four valencies. According
to Raubach (1983) two or more molecules of ortho-silicic acid

can bind with the release of H₂O and thus give rise to

higher acids forming in this process chain, bunch-like and spatial-network
structures. For unknown reasons silicon has “preferred” to remain in a
bound state as a main component of onyx, quartz, achate and silicon
dioxide (SiO₂) or sand — most widely spread on the earth surface.
Sulphur and phosphorus join company at a later stage. Phosphorus
takes an active part in the structure of nucleic acids, which assume the
function of bearers of genetic information and participate in the replication
mechanisms of living creatures.
The increase of oxygen content in the earth atmosphere as a result
mainly of photosynthesis has drastically changed metabolism of living
organisms. The anaerobic release of energy from glucose of 47 kcal is
replaced by the aerobic one in which the released energy is several times
greater — 686 kcal. All possible sources of energy have been subjected to

element with the highest content in the earth mantle — 62.5% (see Table 3)
has not taken an active part in the exchange of substances since it was in a
bound state. Hydrogen, water and carbon dioxide have played the primary
role in these early processes.

If we however have a look at the chemical formulae of the basic
biomolecules — amino acids and nucleic acid bases (see Figs. 2–29 and
2–37 A), we shall got easily convinced that alongside carbon, hydrogen and
nitrogen, oxygen also takes part in them.
The question crops up: where has oxygen come from? It could have
come from the compounds in which it has been bound or from water and
carbon dioxide. The second assumption seems more plausible.
Most obviously oxygen has been “prevented” from taking part in the
primeval metabolic process. Hydrogen was entirely another case. This is
the lightest chemical element with a high reaction capacity and has been
found in various physical states: nascent atoms (H), ions (H+), as well as
bound to other atoms. That is why it has actively participated in the
synthesis of biomolecules and the metabolic processes. Its content in the
human organism is the highest — 60.3%. It is no wonder that the hydrogen
ion concentration i.e. pH is of such an importance for the life processes and
chemical reactions in the cells. The oxygen content in human organism is
also high — 25.5%. This can be assumed to be due to its later accumulation
in a free state (O₂) in the atmosphere as a result mainly of photosynthesis.
The reverse tendency is observed with carbon and nitrogen. From
minimal quantities in the lithosphere these two elements have reached high
percentage in the human organism (10.5% and 2.42% respectively). This

these microorganisms has been H₂S, which releases sulphur accumulated
in the environment after its participation in the reduction process. The green
sulphur bacteria also use H₂S according to the following equation:

Lehninger has also stated that photosynthesizing bacteria do not use
and do not release molecular oxygen. Instead of H₂O they use as donors of
electrons inorganic substances (hydrogen sulphide, thiosulphate, gaseous
hydrogen), as well as organic compounds (lactic acid, alcohols, etc.).
Organisms not releasing oxygen do not possess photosystem II.
Using more precise methods it was established that CO₂ is not always
the acceptor of electrons. In some cases (in higher plants) this role is
played by nitrates. In nitrogen fixing photosynthesizing organisms CO2 can
be the acceptor of electrons as well as molecular nitrogen (N₂), which is
thus oxidized to ammonia (NH₃). Hydrogen ions (H+) can also play such a
role resulting in the formation of molecular hydrogen (H₂).
In different organisms photosynthesis can take place with the
participation of different donors and acceptors of electrons. The process
can be summed up as follows:

where D.H₂ is the donor, and A — the acceptor of the electrons or the
hydrogen atoms.
It has been initially assumed that molecular oxygen released in
photosynthesis comes from CO₂. In 1931 van Niel has suggested for it to
originate from water molecules, which was later confirmed by a number of
experiments including such with labelled isotopes (¹⁸O). In order to
emphasize upon its origin the summed up equation of photosynthesis is
presented in the following manner:

The process of photosynthesis engages a large number of enzymes,
different pigments organized in cellular organelles (mainly chloroplasts) and
the macroergic bonds of ATP formed by the way of phosphorylation. Their
indetail account is quite intentionally skipped so that the development of
metabolism could be better outlined from an evolutionary standpoint.
As far as living entities are closely associated with metabolism, the
review in retrospect gives a certain idea of the initial stages of development of
life. At the very beginning nascent oxygen (O₂) was not present in earth
atmosphere, or it was but in minimal quantities. For that reason this chemical