This is the second in a series of essays about Gaia.
One of the great insights of modern science has been that the ecosystem of the Earth as a whole might be self-regulating, that is, it regulates its systems (temperature, geology, atmospheric chemistry, biology) the way a body regulates itself. It adds a new dimension to the meaning of Mother Earth. This is an insight usually attributed to James Lovelock, who called the Earth Gaia, and extended by the late, great biologist Lynn Margulis. Neither one of them intended to imply that the Earth was a goddess; Lynn Margulis particularly told me so. Gaia is a self-regulating systems, not a goddess.
In this series of essays, I wish to explain that Earth has a regulatory system, which you can call Gaia if you like. But this system is very unresponsive except on the largest scales of time and space. Don’t trust Gaia to solve any of our current ecological problems.
Perhaps Gaia is the reason Earth’s climate has been stable for over 500 million years? No, because the climate and atmosphere have not been stable.
The Earth has had five major extinctions (not counting the sixth, going on as we speak) and several minor extinctions. Gaia was, apparently, unable to prevent those from happening.
When plant life started covering the land surface, over 400 million years ago, photosynthesis increased dramatically, removing a lot of carbon dioxide from the air. Forests covered much of the land surface. These forests would not have looked like the thick modern tropical jungles; there was apparently space between the trees, making them more of a woodland than a forest. But there was an even more important difference between the forests 400 million years ago and today. Back then, when trees died, they fell into shallow water and piled up in mass graves, eventually becoming coal. Today, when trees die, they seldom form coal. Instead, they decompose. The reason appears to be that fungi, the most important modern decomposers of wood and other plant tissues, had not yet evolved the ability to digest wood. Coal—that is where the Carboniferous Period of Earth history got its name.
Photosynthesis removed a lot of carbon from the air, and it got stored underground in coal seams. Meanwhile, where did the photosynthetic oxygen go? Into the air, of course. Today, the air is about 21 percent oxygen; during the Carboniferous it got as high as 35 percent. If you had been there, you would have hyper-oxygenated. With that much oxygen, fires would have been widespread, even on wet plant tissue. Evidence from the fossil record suggests that this was what happened.
The oxygenated atmosphere was also very dense. That is why giant insects, such as giant dragonflies, which today would not have been able to get off the ground, could fly. Insects, moreover, breathe through little tubes in their abdomens. Today an arthropod that is too large could not breathe, because its breathing tube surface areas would not have grown as much as its metabolizing volume. There was so much oxygen that the giant dragonflies could fly and there were giant millipedes.
Gaia did not prevent this oxygen buildup, nor the removal of carbon dioxide which might have led to global cooling. Carbon dioxide was running out, and one of the evolutionary responses was that plants increased their carbon-absorbing surfaces: they evolved leaves for the first time, instead of just absorbing carbon through green stems. This only made the decline in atmospheric carbon more dramatic.
The oxygen buildup would not have occurred forever, because with too much oxygen, life would have risked extinction, including plant life, almost the sole source of oxygen in the atmosphere. In this way also, Gaia regulated the atmosphere, but only within very broad bounds, careening toward disaster without actually reaching it.
Gaia has no mind and is slow. It may have saved Earth from becoming an ice planet or a hellish one. But on a day to day, or million year to million year, basis, it is of little help to the planet.
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