Organisation at the Ecosystem Level 67
of photosynthesis. Through various chemical reactions, the atmosphere
transformed into its present composition, which mainly contains nitrogen,
oxygen and small quantities of argon, water vapours and carbon dioxide. A
decisive parameter in the development and propagation of living organisms
was the ozone layer in the stratosphere; it was created when oxygen reached
an important concentration in the atmosphere. The ozone layer began to
protect life against the sun’s ultraviolet radiation (Chapter 9). Thanks to
that protection, living organisms were able to survive out of the water,
plenty of forests grew on land and photosynthesis dominated. It is estimated
that the total amount of oxygen produced by plants during Earth’s history
is tenfold the amount present in the atmosphere today. Therefore, the corresponding amount of carbon dioxide has been removed from the atmosphere
through photosynthesis.
With the stabilisation of the carbon cycle, the atmosphere’s composition became approximately similar to the present one and has since been
stable. For millions of years, stability prevailed, with plant production consuming, almost completely, all living organism’s respiration. However, as
early as the 19th century, this balance had been upset. Extensive deforestation and use of fossil fuels have released large amounts of carbon into the
atmosphere, in a CO 2 form; these had remained stored in forest biomass
or fuels respectively. At present, humans, with the extensive use of fossil
fuels reserves, consume in a year as much O 2 as photosynthesis produced in
1000 years. Without human interference, the carbon in fossil fuels would
leak slowly into the atmosphere through volcanic activity over millions of
years. Humans accelerate the process, releasing carbon that took millions
of years to accumulate. In 2009, humans released about 8.4 billion tons
of carbon into the atmosphere. This reversal, though, of natural processes
does not create a threat of O 2 deficiency, since its quantities in the atmosphere are quite large and its consumption negligible compared to them
(Chapter 4, Section 4.3.4). However, CO 2 excess poses risks, since its presence in the atmosphere is small and its percentage has been significantly
increased (Chapter 9). It is estimated that atmospheric air’s CO 2 was in
an analogy of 290 ppm in the middle of the 19th century; it has reached
415 ppm in 2021.
4.3.3 Nitrogen Cycle
Nitrogen is necessary for the creation of proteins. Despite its abundant presence in the atmosphere in its molecular form, it is chemically inactive and
cannot be easily broken down by organisms. Most producer organisms can
only absorb the nitrogen in the forms of ammonium nitrate (NH 4 ) + and
nitrogen nitrate (NO3) – . Thus, even though atmospheric N 2 constitutes a
huge storage, its cycle, and along with it the life process in our planet, are
limited by the conversion speed of atmospheric N 2 to its usable bound forms.
of photosynthesis. Through various chemical reactions, the atmosphere
transformed into its present composition, which mainly contains nitrogen,
oxygen and small quantities of argon, water vapours and carbon dioxide. A
decisive parameter in the development and propagation of living organisms
was the ozone layer in the stratosphere; it was created when oxygen reached
an important concentration in the atmosphere. The ozone layer began to
protect life against the sun’s ultraviolet radiation (Chapter 9). Thanks to
that protection, living organisms were able to survive out of the water,
plenty of forests grew on land and photosynthesis dominated. It is estimated
that the total amount of oxygen produced by plants during Earth’s history
is tenfold the amount present in the atmosphere today. Therefore, the corresponding amount of carbon dioxide has been removed from the atmosphere
through photosynthesis.
With the stabilisation of the carbon cycle, the atmosphere’s composition became approximately similar to the present one and has since been
stable. For millions of years, stability prevailed, with plant production consuming, almost completely, all living organism’s respiration. However, as
early as the 19th century, this balance had been upset. Extensive deforestation and use of fossil fuels have released large amounts of carbon into the
atmosphere, in a CO 2 form; these had remained stored in forest biomass
or fuels respectively. At present, humans, with the extensive use of fossil
fuels reserves, consume in a year as much O 2 as photosynthesis produced in
1000 years. Without human interference, the carbon in fossil fuels would
leak slowly into the atmosphere through volcanic activity over millions of
years. Humans accelerate the process, releasing carbon that took millions
of years to accumulate. In 2009, humans released about 8.4 billion tons
of carbon into the atmosphere. This reversal, though, of natural processes
does not create a threat of O 2 deficiency, since its quantities in the atmosphere are quite large and its consumption negligible compared to them
(Chapter 4, Section 4.3.4). However, CO 2 excess poses risks, since its presence in the atmosphere is small and its percentage has been significantly
increased (Chapter 9). It is estimated that atmospheric air’s CO 2 was in
an analogy of 290 ppm in the middle of the 19th century; it has reached
415 ppm in 2021.
4.3.3 Nitrogen Cycle
Nitrogen is necessary for the creation of proteins. Despite its abundant presence in the atmosphere in its molecular form, it is chemically inactive and
cannot be easily broken down by organisms. Most producer organisms can
only absorb the nitrogen in the forms of ammonium nitrate (NH 4 ) + and
nitrogen nitrate (NO3) – . Thus, even though atmospheric N 2 constitutes a
huge storage, its cycle, and along with it the life process in our planet, are
limited by the conversion speed of atmospheric N 2 to its usable bound forms.