Our planet can be considered globally as a living organism in which each single part interacts with the others in an extremely delicate way. Human activities, which often alter this equilibrium, lead to a homeostatic reaction that tends to re-establish the loss (or missing) equilibrium by eliminating all the perturbant elements. Actually, Earth's atmosphere has never been unchangeable: its composition, temperature and auto-depuration ability have continuously fluctuated since the planet's formation. …
