James Lovelock's Gaia Hypothesis: Past, Present, and Future

By Michael Farb 
Introduction to Gaia
What is life? It's not an easy question to answer, that's for sure. Most of us have a general idea of what it means to be alive. We know ourselves to be living, breathing, creatures. We know we need to sustain ourselves with energy, through our food sources (or the supermarket).

Relative to inanimate objects we are alive. The chair I sit in at my desk is certainly not alive. The tree outside my window is alive. I can see it grow and change as its climate changes, I can even look under a microscope at a sample of its cells in a leaf. If plucked early enough from its branches, I may be able to see the movement of tiny organelles, facilitating the flow of nutrients though a complex system of cells and veins. Such experiments on my chair would not reveal such activity. James Lovelock would not agree with all the above assertions. Lovelock is the founder of a highly debated theory about earth science and biology called the Gaia hypothesis. Lovelock would posit that my chair, I, my desk, the tree outside my window, and the very air I breathe are all part of a living organism called Gaia. The Gaia hypothesis attempts to prove that the air, waters, rock, and life on Earth are all interconnected. An answer to scientists who study biology without concerning themselves with the effects of climate on life and vice versa, the Gaia hypothesis is a grand synthesis of the climate and life of Earth. What is life? Lovelock might say, "You're looking at it."
 
 

PAST HISTORY

Principles of the Gaia Hypothesis
Lovelock (1979) defines the Gaia hypothesis as follows:
 
 
This postulates that the physical and chemical condition of the surface of the Earth, of the atmosphere, and of the oceans has been and is actively made fit and comfortable by the presence of life itself.
Additionally, he goes on to provide a disclaimer to his hypothesis. "This is in contrast to the conventional wisdom which held that life adapted to the planetary conditions as it and they evolved their separate ways." In light of Lovelock's second statement, the Gaia hypothesis attempts to bring synthesis to the ideas of evolutionary biologists and those of the climatologists (Lovelock 1988). When figuring equations for population growth on a herd of caribou, biologists do not often take into account the amount of ultraviolet radiation received by the herd. The results of such an inclusion would be negligible at best. On the same note, climatologists pay little attention to sulfur-producing phytoplankton when computing rainfall patterns. A synthesis of both spheres of science provides a much broader-based theory. Gaia theory is to planetary science, what plate tectonics is to geological science.

 But then we might say, "Why bother? The Earth is almost all rock, and you expect me to believe it's alive?" Lovelock's counter to this argument lies in an example provided by physicist Jerome Rothstein (Lovelock 1988). Rothstein observed that the concept might be grasped easier if you let the "image of a giant redwood tree enter your mind." Our science has proven the tree to be alive, yet almost all of the tree is dead. The redwood is a giant tower of dead wood fibers made by its ancestors (as it is with all trees). Each year, as a tree grows, it grows a new "skin" around the dead or dying "skin" of the previous year. The only living part of the tree exists around a dead hulk. In a similar way the Earth is alive. It too is composed of a thin "skin" of life surrounding a dead hulk of rock.
 
 

James Lovelock and the Evolution of the Gaia Hypothesis
Lovelock first got involved with Gaia theory as a result of working with NASA to predict if the planet Mars held life or not. In the mid-1960's, Lovelock was approached by NASA, who asked him for help in searching for life on Mars. In 1965, Lovelock proposed some physical tests for determining whether Mars held life or not. Instead of a local physical site at the point of a hard probe landing (search -- up), he proposed that a top-down view of the entire planet be employed. The test would analyze the composition of the planet's atmosphere. If it held no life, the planet should have an atmosphere close to the chemical equilibrium state, as determined by chemistry and physics. If the planet held life, the life on the planet would use the atmosphere as a source for raw materials and a waste depository (Lovelock 1990). This kind of disequilibrium would indicate the presence of life (as we know it).

 Upon joining with scientist Dian Hitchcock, she and Lovelock examined the atmospheric data from infrared astronomy done on Mars. That data, contrasted with similar data on the normal distribution of gases in the Earth's atmosphere provided a striking difference. The Martian atmosphere was in a state of stable chemical equilibrium, while the Earth was shown to be in a state of deep chemical disequilibrium. The anomalies in our atmosphere were not to be found on Mars. The two scientists concluded that Mars was probably lifeless; almost 10 years before Viking 1 and 2 would come up with the same results. Such a top-down approach to the planetary atmosphere led Lovelock to view our own planet as a whole, from outer space; rather than from the inside-out (Lovelock 1979, 1988, 1990).

 In that same year, Lovelock (1990) began to think that such an unlikely combination of gases such as the Earth had, with the ability to keep itself in a stable state, must have an "active control system" to maintain it. His initial assumption was that this active control system would somehow include the organisms on the Earth's surface. By the end of the 1960's, Lovelock had definitively organized his theory. Novelist William Golding, Lovelock's neighbor, suggested he call the control system Gaia, after the Greek's Earth goddess. The name for the complex system of climate control has remained "Gaia" since then, taking on a "life" of its own at times.

 First on his own in 1972, and then later in 1973 with biologist Lynn Margulis, Lovelock formally proposed the idea of Gaia as a control system. By 1973, they had refined the Gaia hypothesis in publications of Tellus and Icarus to be "the notion of the biosphere as an adaptive control system that can maintain the Earth in homeostasis." (Lovelock 1990). Also, in his 1988 book, Lovelock states that "Gaia theory predicts that the climate and chemical composition of the Earth are kept in homeostasis for long periods until some internal contradiction or external force causes a jump to a new stable state." This statement provides Gaia with the ability to alter itself and adapt to a changing environment. Since the very first unicellular organisms, the Earth has not been without life. Even with changes both drastic and punctuated, Gaia has been able to alter both the climate and the life of Earth to survive.
 
 

Daisyworld
Much of the criticism put to the Gaia hypothesis involves the complaint that Gaia theory is teleological and vague. Lovelock's response to this was to create a "drastic simplification" of the Gaia hypothesis. He created a system called Daisyworld to provide his critics with a mathematical example of Gaia theory.

 Lovelock (1988) writes about Daisyworld:
 
 

Picture a planet about the same size as the Earth, spinning on its axis and orbiting, at the same distance as the Earth, a star of the same mass and luminosity as the Sun. This planet differs from the Earth in having more land area and less ocean, but it is well watered, and plants will grow almost anywhere on the land surfaces when the climate is right. This is the planet Daisyworld, so called because the principal plant species are daises of different shades of color: some dark, some light, and some neutral colors in between.
Lovelock goes on to define other important details of the Daisyworld system and its native species. The star warming Daisyworld increases its heat output over time. The environment is simplified as well. Its only component of concern is temperature and the biota, daisies. If the temperature is too cold (below 5ûC) the daisies will not grow, or too hot (above 40ûC) and the daisies will wither and die. They survive best at around 20ûC. Daisyworld has a constant amount of carbon dioxide, just enough for the daisies. There are no clouds during the day, and rain falls at night. Most importantly, dark daisies will dominate the population when the solar output is low (and thus absorbing more sunlight), and light daisies will dominate the population when the solar output is high (reflecting excess sunlight out to space). The number of daisies with dark or light colors to them are controlled by the system as a whole. Since all daisies want to exist at optimum conditions (20ûC), the number of light daises will increase and the number of dark daisies will decrease over time, as solar output increases, to keep the mean temperature of the planet at or near the 20ûC mark.

 Using equations borrowed from theoretical ecology, Lovelock ran several scenarios on his personal computer given the Daisyworld parameters. He found that the daisies did in fact keep the temperature to within 5û of 20ûC, until solar luminosity was so high that all the daisies died out in a ball of flame. Given the time range of the first growth of daisies and their total eventual demise, he found that diversity among the daisies peaked near the middle of that range, which is also where the total population of daisies was most evenly distributed across the spectrum of dark to light daisies. This mathematical approach proved Lovelock's point about the controlled stability of the climate by the life present as not being teleological. At the same time, we can also see that the Daisyworld is not real. It looks very nice and neat, and even illustrates some interesting points about climate control by the biota, but ultimately is not real evidence. These computer simulations may help us to figure out where to look for evidence, but will not provide us with all the answers. The proof of an active planetary control system will ultimately lie in empirical evidence, not computer simulations.
 
 

PRESENT SUPPORT AND CRITICISM

Lynn Margulis cites four different examples of biological or chemical processes that might be part of the system whereby Gaia regulates itself (Mann 1991). However, strong criticism still exists for some of these assertions.
 
 
Carbon Dioxide
First is the support for the carbon dioxide cycle. Over the past 3.8 billion years that life has been present on Earth, temperatures on Earth have remained roughly constant while the Sun's luminosity has increased about one quarter. It is believed that the drop in the atmosphere's ability to absorb solar radiation is due to a global decline in carbon dioxide levels over that time. The biosphere would have attempted to fix carbon dioxide in the form of the calcium carbonate of marine shells (Mann 1991).

 Critics say that the global decline of carbon dioxide could have been due to rainwater that dissolves carbon dioxide to form carbonic acid, which then dissolves calcified rocks. The then neutralized acid will run into the sea, performing chemical weathering of said rocks along the way (Schneider 1990).
 
 

Plate Tectonics
A sudden drop in temperature millions of years ago, possibly due to life reducing the carbon dioxide levels (as mentioned above), may also affect plate tectonics. If this sudden drop in temperature chilled the upper mantle of the Earth's crust, it might have destabilized the lower crust resulting in plate tectonic shifting of continents (Mann 1991).
 
 
Dimethyl Sulfide Production
Third, phytoplankton may have part of the control in that they produce dimethyl sulfide. They release this dimethyl sulfide into the air, which is then converted into drops sulfuric acid, which in turn become nuclei for cloud condensation (Monastersky 1987, Lindley 1988, Mann 1991, Fell and Liss 1993). These nuclei help to produce thicker clouds, blocking more of the sun, and cooling the oceans.

 This scenario might suggest that this interaction might not work in Gaia's favor, by cooling the oceans, instead of warming them. This is assuming that the trend for ocean temperature is to a cooler state. The feedback loop would enhance ice ages. Countering this counter-argument, Lovelock (Kerr 1988) states that Gaia may favor an ice age as the optimum temperature.
 
 

Oceanic Salinity
Natural geologic weathering releases salts into the oceans too fast for life to adapt at the same rate. At the same time, geological evidence indicates that the oceans have remained at a constant salinity of 10% saturation for millions of years. Salt flats, which are hosts to dense patches of bacteria, may be removing the salt from the oceans. The bacteria, surviving in water too salty for any other life, trap salts and other minerals to form a sheath within which the bacterial colonies live (Mann 1991).
 
 

FUTURE

Conclusion: Is Gaia Theory Still Valid?
A less aggressive approach to the Gaia hypothesis may be more fruitful in the long term. Richard Kerr (1988) reports that since the "traditional, teleological, strong hypothesis is simply not testable," that this "strong" version of Gaia should be abandoned for a "weaker" version. The "weaker" forms of Gaia, in which life only influences environment, are "so obviously correct that they do not merit status as hypotheses" (Kerr 1988). Lovelock himself admitted that the strong Gaia must be abandoned. Earlier I likened the Gaia hypothesis to plate tectonics. Again I think it is appropriate here to do so. Plate tectonics has been the hottest new theory in the field of geology since the 1960's, but most geologists do not put all of their faith in it as the ultimate drive behind all geological processes. The same can be said of the Gaia hypothesis. It may help us solve some global environmental questions in the future, but we must not rest the entire weight of our faith upon it. Gaia is fragile, at some point, it may break.
 
 

Works Cited

Fell, Nolan and Peter Liss. "Can algae cool the planet?" New Scientist 21 August 1993: 34-38.

 Kerr, Richard A. "No Longer Willful, Gaia Becomes Respectable." Science 22 April 1988: 393-395.

 Lindley, David. "Is the Earth alive or dead?" Nature 7 April 1988: 483-484.

 Lovelock, James E. Gaia, a New Look at Life on Earth. Oxford University Press: Oxford, 1979.

 Lovelock, James E. The Ages of Gaia, a Biography of Our Living Earth. Bantam Books: New York, 1988.

Lovelock, James E. "Hands up for the Gaia hypothesis." Nature 8 March 1990: 100-102.

 Mann, Charles. "Lynn Margulis: Science's Unruly Earth Mother." Science 19 April 1991: 378-381.

 Monastersky, Richard. "The Plankton-Climate Connection." Science News 5 December 1987: 362-365.

 Schnieder, Stephen H. "Debating Gaia." Environment May 1990:5-8+.
 
 

©1995 by Michael Farb. All portions of this document may be reproduced in whole or in part for educational purposes provided credit is given to the author.