How the Earth will end us
The Gaia hypotheses, as it was originally proposed by James Lovelock in his book “Gaia: A New Look at Life on Earth”, suggests that the Earth self regulates. Let me elaborate.
Through the course of its life, planet Earth has undergone many changes. Sometimes, frequent volcanic eruptions have overheated the atmosphere by filling it with ash and greenhouse gases, sometimes external forces like massive asteroids have seriously damaged the atmosphere and the geography of the world.
Lovelock noticed that in spite of all these factors, the proportion of gases in Earth's atmosphere has remained more or less the same, ever since life took off as a dominant phenomenon. The technical term for this is “homoeostasis”.
This is a very important observation because the state of life on Earth relies to a heavy degree on the balance of gases in the atmosphere. Even seemingly tiny shifts in this delicate balance can seriously affect the planet's life-supporting capacity. Lovelock compared this to atmospheres of other planets like Mars (which was a curiosity among scientists back then as far as life is considered) and predicted that Mars is a dead planet. The planet's atmosphere didn't reveal any signs of homoeostasis upon telescopic observation. Later missions proved him right. Mars is dead, as far as life of the Earthly kind (carbon-based, oxygen-breathing) is concerned.
Lovelock came to the conclusion that there is something about the Earth system that constantly regulates the state of the atmosphere to keep it in that delicate life-supporting state. Gaia is simply the name he gave to that phenomenon.
While the theory was strongly contested when it first came out, recent years have found many new takers for it. Because of the obviously semi-religious connotations of the theory, some quarters have interpreted it differently, giving it a magical colour. But for anyone interested in knowing more, I recommend Googling “James Lovelock Gaia”.
Lovelock also makes some dire predictions for our future as a species. He says that global warming (regardless of whether it is man-made or natural), is pushing the boundaries of the Gaia principle. Gaia moderates the balance of life by switching species on and off. For example, if a certain species of rodent becomes too numerous in a certain habitat and starts to seriously threaten the balance by consuming its resources too quickly, nature brings into being forces that may eradicate or contain the rodent species. This can be in the form of a superior hunter species, or a disease-carrying virus that would wipe the species out without affecting much else.
If humans continue to be a threat to the balance of life, it is entirely possible (says Lovelock) that nature would quickly and quietly wipe us out while letting the rest of Earthly life remain.