The Gaia hypothesis was developed by microbiologist Lynn Margulis and chemist, biophysicist and physician James Lovelock in the mid-1960s. It states that the Earth and its entire biosphere can be regarded as a living being; in the sense that the biosphere - the totality of all organisms - creates and maintains conditions that enable not only life but also the evolution of more complex organisms. The Earth's surface thus forms a dynamic system that stabilizes the entire biosphere through feedback mechanisms. This hypothesis presupposes a certain definition of life, according to which living beings are characterized in particular by their ability to self-organize or autopoiesis. The term derives from Gaia, the earth goddess and great mother of Greek mythology. The Gaia hypothesis gave rise to the physiology of the earth (geophysiology).
Molecular oxygen is a highly reactive substance that quickly binds to other elements and thus disappears. Iron rust, wood burns. What is amazing, however, is that the oxygen content of the atmosphere is constant: no matter how much iron rusts and how much wood burns, the global oxygen content remains unchanged. This becomes particularly exciting when one considers that "fossil air" from ice cores or amber has a very similar, often the same composition as today. Obviously, since life in the countryside has been active, the oxygen content of the air has changed only insignificantly. The Gaia hypothesis says that the "life" system itself keeps the proportion stable.
Example of climate fluctuations
There is increasing evidence that until 600 million years ago the climate was subject to extreme fluctuations that have not occurred since. At times, the earth was literally covered by an ice shield ("snowball earth"), while at other times it was completely ice-free. Critics of the Gaia hypothesis therefore argue that such extreme fluctuations contradict the idea of a balanced Earth.
Supporter see it the other way round: One explanation for these early climate fluctuations is that there were no complex organisms with skeletons or calcareous shells at that early time (Precambrian). This is because the calcareous marine plankton plays an enormous role in the CO2 balance of the oceans today. When these organisms grow, they absorb carbon dioxide (CO2) from the water, and when they die again, they sink together with their calcareous shells to the seabed, where massive calcareous sediments form over millions of years. In this way, the CO2 content of the oceans - and thus indirectly that of the atmosphere - is chemically stabilised. The formation of these organisms would therefore have contributed to stabilizing and thus improving the living conditions on Earth.
Example salt content of the oceans
The salt content of the oceans is constant at 3.5%. Although considerable quantities of minerals continue to be dissolved by land and shipped into the sea, the salt content has not risen for millions of years. If one assumes that the mineral load in earlier times was as high as it is today, there would now have to be so much salt in the oceans that higher forms of life could no longer exist. In fact, there are processes that remove salt from the ocean. These include the formation of lagoons and closed sea basins in which seawater collects, evaporates and in this way forms powerful salt deposits. Reef-forming organisms are involved in the formation of such lagoons. According to Lovelock, this is also a process in which the community of living beings itself ensures that their living conditions are preserved. On the other hand, methyl chloride and methyl iodide are produced by marine algae and then released into the atmosphere. This biological process also removes salt components such as chlorine from seawater.
The origins of the Gaia hypothesis lie in the scientific background of the two researchers James Lovelock and Lynn Margulis. The geochemist Lovelock has studied intensively how the biosphere has changed and still changes the earth's atmosphere in the course of the earth's history. One result of these considerations is the CLAW hypothesis, which was formulated at the end of the 1980s and relates to the relationship between phytoplankton and the global climate. These phenomena, wrote Lovelock, are understandable only if the planet is seen as a single living organism.
The Gaia hypothesis is based on a systems theoretical understanding of life. According to this hypothesis, a living being is an open and entropy-producing system that can adapt reactively and self-organizingly to its environment in such a way that it is able to adapt to its environment by procreation.
A good video on the topic can be found here
Here you can find good background information on the topic of the Earth's ecosystem (in German)