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http://www.marxists.org/reference/subject/philosophy/works/us/gaia.htm
Life first appeared on the Earth about 3,500 million years ago. From that time until now, the presence of fossils shows that the Earth’s climate has changed very little. Yet the output of heat from the sun, the surface properties of the Earth, and the composition of the atmosphere have almost certainly varied greatly over the same period.
The chemical composition of the atmosphere bears no relation to the expectations of steady-state chemical equilibrium. The presence of methane, nitrous oxide, and even nitrogen in our present oxidising atmosphere represents violation of the rules of chemistry to be measured in tens of orders of magnitude. Disequilibria on this scale suggest that the atmosphere is not merely a biological product, but more probably a biological construction: not living, but like a cat’s fur, a bird’s feathers, or the paper of a wasp’s nest, an extension of a living system designed to maintain a chosen environment. Thus the atmospheric concentration of gases such as oxygen and ammonia is found to be kept at an optimum value from which even small departures could have disastrous consequences for life.
The climate and the chemical properties of the Earth now and throughout its history seem always to have been optimal for life. For this to have happened by chance is as unlikely as to survive unscathed a drive blindfold through rush-hour traffic.
Source: Gaia A new look at life on Earth by J E Lovelock, publ. Oxford University Press 1979.
...the presence of fossils shows that the Earth’s climate has changed very little...