Gaia What'sNEWIs it too much to suggest that we may recognize... the beauty and fittingness of an environment created by an assembly of creatures? — James Lovelock (1)Regardless of the paradigm we use to explain it, life on Earth has evolved from bacteria, to single-celled eukaryotic creatures, to multicelled animals and plants, to animals and plants with highly specialized organs and systems. This truth we can all accept. The environment of Earth has also evolved. Earth has cooled, the temperature has stabilized, and the composition of the atmosphere has completely changed. Under the current paradigm, the two parallel evolutions affect each other, but not in any coordinated way. Life consumes resources and discharges waste products; both processes alter the environment. As the environment changes, it presents new challenges to life. So far, luckily, life has been able to meet the challenges. That's the orthodoxy. The Oxygen Atmosphere
The most important change in Earth's environment since life began is the buildup of free oxygen in the air. Before life became established on Earth, the air contained no free oxygen. Today, the atmosphere is 21 percent oxygen. Although small amounts of oxygen were present very soon after life appeared, the significant buildup probably began about two billion years ago. By the time of the Cambrian Explosion, 570 million years ago, the oxygen content had to be approximately as high as it is today.
There is evidence that the beginning of the oxygen buildup coincides with the appearance of the first eukaryotic cells. Most bacteria don't require oxygen, and many are poisoned by oxygen. All eukaryotic cells require oxygen for their more complicated and more efficient metabolism. Furthermore, there has to be oxygen for there to be ozone. Ozone shields the surface of Earth from damaging ultraviolet rays. Only with such shielding can life come out from under water or underground and begin to live on the surface (2):
It is widely believed that 2000 million years ago the cyanobacteria — oxygen eliminating photosynthetic prokaryotes that used to be called blue-green algae... effected one of the greatest changes this planet has ever known: the increase in concentration of atmospheric oxygen from far less than 1% to about 20%. Without this concentration of oxygen, people and other animals would have never evolved. The orthodox understanding of this event is that when the oxygen began to accumulate, it constituted a wholesale pollution of the environment, a "holocaust" upon the bacteria of Earth (3, 4). Chance mutations in the genes of some bacteria enabled them to endure the oxygen atmosphere and rescued them. At the same time a fortunate symbiosis between bacteria and the formerly free-living mitochondria enabled eukaryotes to evolve in response to the crisis. Oxygen-based metabolism came into being. The environment changed and life randomly followed. True, the oxygen-based system of metabolism in animals and plants is excellent, but in another environment, another metabolic system might have evolved, according to the Darwinian paradigm. James Lovelock
English inventor, atmospheric chemist, winner of the 1996 Volvo Environment Prize and the 1997 Asahi Glass Foundation Blue Planet Prize, James Lovelock thinks there may be a closer connection, a coordination between the evolution of life and the evolution of the environment. He calls his theory Gaia (from the Greek goddess of Earth). The theory, described in his 1979 book Gaia (5), can be paraphrased in different ways. In the preface to Gaia, Lovelock himself writes, "...the biosphere is a self-regulating entity with the capacity to keep our planet healthy by controlling the chemical and physical environment." Others have described the theory as the idea that Earth itself acts like a single organism.
Lovelock believes, for example, that Gaia is at work to keep the oxygen content of the atmosphere high and within the range that all oxygen-breathing animals require. The atmospheres of our two nearest neighbors, Venus and Mars, contain 0.00 percent and 0.13 percent, respectively, of free oxygen. Without life to keep supplying it, Earth wouldn't have any either. Lovelock believes that life regulates the surface temperature of Earth, too. He says the average surface temperature of Earth has remained within a narrow range — between 10 and 20° C — for over three billion years. The temperature, he says, has not varied from the mean by more than 5°C (9° F.) Other research shows that the range could be wider (6), but the constancy of Earth's surface temperature since life became established is still remarkable. During that time the sun's output has increased by thirty (7) or forty (7.1) percent. How has this stability of Earth's temperature been maintained? Even ignoring the long-term trend of the sun, wouldn't the temperature vary more than that? How stable is the temperature on our neighboring planets? In March 1995, the Hubble Space Telescope "weather center" issued a report containing the following: "The higher temperatures and global dust storms on Mars in the 1970s have ended. The skies are now clear and 36 [Fahrenheit] degrees colder, on average, with morning haze and lingering clouds near the volcanoes" (8). Two years later, when the Hubble telescope was again aimed at Mars, even more dramatic changes were noticed (9): Abrupt swings that would devastate civilization if they occurred on Earth are routine on Mars, where the global climate can veer from relatively hot, dusty weather to very cold and cloudy within a matter of days.... On Earth, a change in global average temperature of only a degree or so over decades has raised concerns about global warming. On Mars... the temperature can swing by 80 degrees Fahrenheit wthin days.These reports give strong evidence that a mechanism to keep Earth's surface temperature steady is needed. The fact that Earth's temperature is steady means that the mechanism — whatever it is — is working. Salinity of the SeaLovelock says another example of Gaia in operation is the regulation of the saltiness of seawater. Seawater is about 3.4 percent salt by weight, and has probably been under 4 percent for as far back as we have data. If it ever rose to over 6 percent, all the life in the sea (except maybe for some archaebacteria) would be killed. Lovelock calculated that the entire salt content of the oceans is replaced every sixty million years by material carried from the continents in rivers and by material vented from below the ocean floor where it is spreading (10). Some other process must constantly remove the salt or else it would keep accumulating in seawater. This accumulation happens in seas where the removal process is not available, such as the Great Salt Lake and the Dead Sea.The process Lovelock likes for preventing excess salt accumulation in the ocean is the evaporation of seawater in shallow lagoons and salt marshes. There seawater is evaporated for recycling, as rain, into fresh water. The salt precipitates out and is buried under layers of sediment. Thus, the shallow lagoons and salt marshes cleanse the oceans as our own kidneys remove impurities from our blood. Lagoons are created by coral reefs, huge biologically created structures. Lagoons gradually fill in, get shallower, and become salt marshes. So coral reefs, which create the necessary lagoons, have an essential, unexpected Gaian purpose (11). The Burial of CarbonAnother Gaian process is the burial of carbon in sedimentary rocks. "A constant rain of carbonate bearing shells sinks toward the ocean floor, where it ultimately forms beds of chalk or limestone rock and thus prevents the stagnation of carbon dioxide in the upper layers of the sea" (12). This process in turn helps regulate the carbon dioxide content of the atmosphere. It may even help to bring about Earth's plate tectonics. Among the solar planets, only Earth has plate tectonics (13). This very slow turning of Earth's crust may be important for life. Life may require the very longterm composting and recycling that plate tectonics accomplishes (14, 15).The Teleological Aspect of Gaia
Partly in response to the accusation of teleology, Lovelock wrote a second book about Gaia entitled The Ages of Gaia, published in 1988 (17). In this work he discusses a new metaphor, "Daisyworld," within which two kinds of daisies unwittingly cooperate to keep the temperature of the planet more constant than it would otherwise be. Lovelock's Daisyworld by itself seems inadequate to overcome the teleological appearance of a big dumb spontaneous Gaia that somehow knows which strings to pull. This doesn't mean that Gaia is a mistaken idea. But it is hard to believe that Gaian processes can evolve by chance. The trials would take too long. For example, one trial of the proposed mechanism for regulating the saltiness of seawater would take at least sixty million years. If Gaia didn't luck upon the right system for that problem on the first try, things would quickly become grim. Gaia makes much more sense if the stabilizing feedback loops were not blindly discovered, but were already available when the need for them arose. This would mean, for example, that the genes for cyanobacteria, for coral, and for animals with carbonate shells were already available when they were needed. Thus, the processes of oxygen accumulation, desalinization of seawater, and burial of carbon would have begun on this planet without delay. Cosmic ancestry would make comprehensible the existence of Gaian processes prior to the establishment of life on Earth.
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C. Scott et al., "Tracing the stepwise oxygenation of the Proterozoic ocean" [
Low oxygen and molybdenum in ancient oceans delayed evolution of life by 2 billion years
2 Feb 2007