Geoscience Reference
In-Depth Information
parameters for later developments, such as the emergence of aerobic
respiration.
Figure 1.3.
The main evolutionary developments and the major
environmental evolutions between the beginnings of life on Earth
(over 3.5 billion years ago) and 400 million years ago
(early Devonian Period) (see color section)
The links of cause and effect between the oxygenation of the
environment and the major developments previous to the emergence
of aerobic respiration are however less evident and still constitute
working hypotheses for research. In the emergence of eukaryotic cells,
it is not unreasonable to assume that prokaryotic cells, subjected to an
increasingly oxygenated environment, were able to find mutual
benefits by sharing respective innovations in the framework of
endosymbiosis [MAR 91]; some taking the best part of their energy
from aerobic respiration (mitochondria) and others furnishing the
protective mechanisms of cytoplasm or DNA against the toxic effects
of oxygen. As far as the emergence of multicellular organization is
concerned, it is not unreasonable to assume that such an organization
