Gaia Theory

Geophysiology and Earth Systems Science

Gaia theory implies that if Earth is a single living system, then planetary science becomes a kind of global physiology (geophysiology) while global environmental management may be conceived as a kind of planetary medicine. It also suggests that the Earth system has a significant capacity to defend itself against a changing external environment. In this respect, it acts like a primitive living creature. When it becomes too warm, it cools itself down, and when it is too cold, it warms itself up. Gaia theorists have collected considerable supporting evidence, but their most powerful single argument involves global temperature.

The traditional scientific argument for the existence of life on Earth is that the planet is perfect for life. This is the so-called Goldilocks hypothesis: Venus is too hot, and Mars is too cold, but the Earth is just right. However, the sun is a star and has the same life cycle. In the past 3.8 billion yrs. (years) of life on Earth, its output has increased by less than 10%. This means that if conditions are just right for life now, they must have been very cold when life began, or if they were perfect when life began, it should be very hot now. However, Earth's temperatures have remained remarkably constant. The oceans have [Page 1176]neither been so hot that they boiled away nor, in the past 0.5 billion yrs., so cold that the whole Earth froze. The reason is climate regulation by changing levels of atmospheric carbon dioxide (CO2). Today, this gas makes up more than 98% of the atmospheres on Mars and Venus but only 0.03% of that of Earth. The missing atmosphere is found sequestered into rocks, such as the limestone rocks that cover an eighth of the planet's land surface, and in all the other organic rocks and sedimentary layers. Most limestone rocks are constructed of small shells. It is life that has buried Earth's excess CO2.

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