Geoscience Reference
In-Depth Information
environmental variability (local climate, deposits of sediment and
drought) and major hazards (volcanic activity, falling asteroids,
notably before and during the last phase of meteoric bombardment
around 4 billion years ago) render the survival of small, local
autonomous ecosystems on timescales in the order of a million years
or more almost impossible.
The question of the “origin” of life in the Earth system is therefore
not only that of the processes by which the first living beings appeared
in general, but it is also that of the conditions that permitted one of
these life forms to become the common ancestor of all life today. How
has life been able to develop into the lattest form, i.e. human beings,
over billions of years, as phylogenetic trees indicate, which stretch
back to a last common ancestor having lived 2 or 3 billion years ago
(
Last Universal Common Ancestor
(LUCA)) and from the findings of
paleontology, which stretch back to around 3.5 billion years ago (the
age of the most ancient known bacterial fossils, in the form of
stromatolites)?
The presence of a sufficiently developed ocean at different
latitudes and in different climates is an element of
enquiry that
concerns the crucial phase of development of the first ecosystems. For
life to have been able to “survive” hazards of all types in the
long-term, it is necessary that its random destruction was only partial
and rapidly compensated by a new colonization of the destroyed
environments. It is necessary to underline here that the colonization is
not a response to the necessity of increasing the chances of survival of
the entirety of the population, but simply that of increasing the
chances of survival of each individual by finding the resources that it
needed elsewhere. The necessity is individual, but its effects extend to
the scale of populations and ecosystems.
There is therefore every reason to think that the life from which
human beings originated appeared and developed in an already
significant ocean. That this origin may have been associated with deep
hydrothermal environments through the use of chemical energy
available at high temperature [REY 01, SHO 96], or rather in the
surface environments through the use of solar energy, is a question that
remains very open to research. Many of the life forms from deep
