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:
- A combination of favourable factors such as temperature, primeval
atmosphere, availability of water in a liquid state, optimal solar
radiation, etc. - 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). - 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