Geoscience Reference
In-Depth Information
its passage to the heart of the system. This transformation is the price
to be paid in order for the level of organization of the system to be
maintained or increased. This is what occurs during photosynthesis in
plants by directly transforming light energy from the Sun, but also
more indirectly, during respiration in animals, plants or bacteria. By
doing so, these reuse, more or less directly, the chemical energy that
the products of the initial photosynthesis contain; that is to say organic
matter (reduced carbon) and oxygen (O
2
).
A stable system does not accumulate energy in the long-term. Apart
from a few insignificant and temporary fluctuations, such as phases of
lipid stocking and the development of living creatures, the entirety of
the adsorbed energy is sent back outside the system, only with a
modification in quality (an increase in entropy). This is, for example,
the case with changes in quality of the energy contained in organic
matter (chemical energy) which, after being used by a living consumer
(via respiration, by using oxygen or another oxidizing compound), is
partly transformed into heat that is then transferred into the
surrounding fluid. In this sense, this flux of energy can be considered a
mediator that reduces the entropy to the system. As entropy is a
physical concept of the measurement of chaos, this reduction results in
the system maintaining or increasing its “order”, otherwise known as
its level of organization.
The Earth, during its accretion phase (around 4.5 billion years ago),
which lasted around 100 million years, was a largely open system which
received a very significant influx of matter relative to the mass already
accumulated. It was in the next phase, during this continued influx of
matter, that terrestrial water, which we know today in the form of oceans,
ice, rivers, lakes, groundwater, clouds and vapor, accumulated on the new
planet. Simple organic molecules, formed in space, also arrived on Earth
during this period. It remained a very open system around 4 billion years
ago during a phase of late and intense meteoric bombardment.
But since this very distant epoch, the Earth has not experienced any
further significant accumulation of matter. Of course, the current
average inward and outward fluxes of matter, at the boundary of the
Earth system, are not null - in the order of several hundreds of
thousands of tons per year - but they are entirely negligible compared
