Gaia: A new look at life on Earth

views updated

Gaia: A new look at life on Earth

Book excerpt

By: James E. Lovelock

Date: 1979

Source: Lovelock, James E. Gaia: A new look at life on Earth. New York: Oxford University Press, 2000.

About the Author: British scientist James Lovelock (1919–) has earned academic degrees in chemistry, medicine, and biophysics. Since 1982, he has been affiliated with the Marine Biological Association at Plymouth, England. He has authored more than two hundred scientific papers in the fields of medicine, biology, instrument science, and geophysiology, and has filed more than fifty patents. His most successful patent was for the electron capture detector, which was used to identify the presence of pesticides in the 1950s. This information was used in Rachel Carson's book Silent Spring, which galvanized public awareness of the environment in the late twentieth century. Lovelock is the author of four books on the Gaia hypothesis.

INTRODUCTION

Lovelock developed the Gaia hypothesis in the 1960s in collaboration with microbiologist Lynn Margulis. Lovelock was asked by NASA scientists at the Jet Propulsion Laboratories to design instruments that would search for life on Mars. As he thought about the problem he realized that any life on Mars would leave a chemical signature in the atmosphere. The Earth's atmosphere contains methane and oxygen, which are chemically reactive. The reason that they both exist in the atmosphere is because they are cycled through living organisms. In contrast, Lovelock showed that the atmosphere of Mars consisted of mostly carbon dioxide and some oxygen. Chemically, the atmosphere was completely non-reactive, and therefore life could not exist on Mars.

This realization led Lovelock to consider how the living and non-living components of Earth interacted to produce a planet that is in equilibrium over long periods of time. Along with biologist Lynn Margulis, Lovelock recognized that a variety of feedback loops between the living and non-living elements of Earth regulate the environment. The ideas resulted in the Gaia hypothesis, which was summarized in the book Gaia: A New Look at Life on Earth in 1979. The fundamental basis of the Gaia hypothesis is that the Earth functions like a single organism. Just as an organism controls its internal systems for its own benefit, so too does the Earth sustain itself in a condition of homeostasis. This means that the Earth regulates the atmosphere, the lithosphere (the Earth) and the hydrosphere (the oceans, rivers, and water vapor) in a way that optimizes conditions for itself. The name Gaia was used in recognition of the ancient Greek goddess, Gaia, who represents the sum of the living and nonliving components of Earth.

According to Lovelock, Gaia's homeostatic system depends on the behavior of living elements of the planet. He points to three areas in which the biotic elements of the planet stabilize the environment: the temperature of the Earth, the salinity of the oceans, and the chemical composition of atmosphere. Lovelock argues that the Sun's energy has increased by 25 percent since Earth was formed; yet Earth's surface temperature has remained constant. He also proposes that the chemical composition of the atmosphere should be unstable, however it is generally constant and could only remain this way because of the contribution of living organisms. Finally Lovelock shows that the salinity of the ocean is constant and demonstrates that living organisms are involved in controlling the ocean's salinity. Lovelock describes how feedback loops in all of these systems stabilize and optimize the environment for the planet.

PRIMARY SOURCE

Introductory As I write, two Viking spacecraft are circling our fellow planet Mars, awaiting landfall instructions from the Earth. Their mission is to search for life, or evidence of life, now or long ago. This book also is about a search for life and the quest for Gaia is an attempt to find the largest living creature on Earth. Our journey may reveal no more than the almost infinite variety of living forms which have proliferated over the Earth's surface under the transparent case of the air and which constitute the biosphere. But if Gaia does exist, then we may find ourselves and all other living things to be parts and partners of a vast being who in her entirety has the power to maintain our planet as a fit and comfortable habitat for life.

The quest for Gaia began more than fifteen years ago, when NASA (the National Aeronautics and Space Administration of the USA) first made plans to look for life on Mars. It is therefore right and proper that this book should open with a tribute to the fantastic Martian voyage of those two mechanical Norsemen.

In the early nineteen-sixties I often visited the Jet Propulsion Laboratories of the California Institute of Technology in Pasadena, as consultant to a team, later to be led by that most able of space biologists Norman Horowitz, whose main objective was to devise ways and means of detecting life on Mars and other planets. Although my particular brief was to advise on some comparatively simple problems of instrument design, as one whose childhood was illuminated by the writings of Jules Verne and Olaf Stapledon I was delighted to have the chance of discussing at first hand the plans for investigating Mars.

At that time, the planning of experiments was mostly based on the assumption that evidence for life on Mars would be much the same as for life on Earth. Thus one proposed series of experiments involved dispatching what was, in effect, an automated microbiological laboratory to sample the Martian soil and judge its suitability to support bacteria, fungi, or other microorganisms. Additional soil experiments were designed to test for chemicals whose presence would indicate life at work: proteins, amino acids, and particularly optically active substances with the capacity that organic matter has to twist a beam of polarized light in a counter-clockwise direction.

After a year or so, and perhaps because I was not directly involved, the euphoria arising from my association with this enthralling problem began to subside, and I found myself asking some rather down-to-earth questions, such as, 'How can we be sure that the Martian way of life, if any, will reveal itself to tests based on Earth's life style?' To say nothing of more difficult questions, such as, 'What is life, and how should it be recognized?'

Some of my still sanguine colleagues at the Jet Propulsion Laboratories mistook my growing skepticism for cynical disillusion and quite properly asked, 'Well, what would you do instead?' At that time I could only reply vaguely, 'I'd look for an entropy reduction, since this must be a general characteristic of all forms of life.' Understandably, this reply was taken to be at the best unpractical and at worst plain obfuscation, for few physical concepts can have caused as much confusion and misunderstanding as has that of entropy.

It is almost a synonym for disorder and yet, as a measure of the rate of dissipation of a system's thermal energy, it can be precisely expressed in mathematical terms. It has been the bane of generations of students and is direfully associated in many minds with decline and decay, since its expression in the Second Law of Thermodynamics (indicating that all energy will eventually dissipate into heat universally distributed and will no longer be available for the performance of useful work) implies the predestined and inevitable run-down and death of the Universe….

The design of a universal life-detection experiment based on entropy reduction seemed at this time to be a somewhat unpromising exercise. However, assuming that life on any planet would be bound to use the fluid media—oceans, atmosphere, or both—as conveyor-belts for raw materials and waste products, it occurred to me that some of the activity associated with concentrated entropy reduction within a living system might spill over into the conveyor-belt regions and alter their composition. The atmosphere of a life-bearing planet would thus become recognizably different from that of a dead planet.

Mars has no oceans. If life had established itself there, it would have had to make use of the atmosphere or stagnate. Mars therefore seemed a suitable planet for a life-detection exercise based on chemical analysis of the atmosphere. Moreover, this could be carried out regardless of the choice of landing site. Most life-detection experiments are effective only within a suitable target area. Even on Earth, local search techniques would be unlikely to yield much positive evidence of life if the landfall occurred on the Antarctic ice sheet or the Sahara desert or in the middle of a salt lake.

While I was thinking on these lines, Dian Hitchcock visited the Jet Propulsion Laboratories. Her task was to compare and evaluate the logic and information-potential of the many suggestions for detecting life on Mars. The notion of life detection by atmospheric analysis appealed to her, and we began developing the idea together. Using our own planet as a model, we examined the extent to which simple knowledge of the chemical composition of the Earth's atmosphere, when coupled with such readily accessible information as the degree of solar radiation and the presence of oceans as well as land masses on the Earth's surface, could provide evidence for life.

Our results convinced us that the only feasible explanation of the Earth's highly improbable atmosphere was that it was being manipulated on a day-to-day basis from the surface, and that the manipulator was life itself. The significant decrease in entropy—or, as a chemist would put it, the persistent state of disequilibrium among the atmospheric gases—was on its own clear proof of life's activity. Take, for example, the simultaneous presence of methane and oxygen in our atmosphere. In sunlight, these two gases react chemically to give carbon dioxide and water vapour. The rate of this reaction is such that to sustain the amount of methane always present in the air, at least 500 million tons of this gas must be introduced into the atmosphere yearly. In addition, there must be some means of replacing the oxygen used up in oxidizing methane and this requires a production of at least twice as much oxygen as methane. The quantities of both of these gases required to keep the Earth's extraordinary atmospheric mixture constant was improbable on a biological basis by at least 100 orders of magnitude.

Here, in one comparatively simple test, was convincing evidence for life on Earth, evidence moreover which could be picked up by an infra-red telescope sited as far away as Mars.

SIGNIFICANCE

The initial reaction to the Gaia hypothesis by the scientific community was highly critical. They claimed it was teleological, which means that it provides a conscious purpose for an observation with a scientific explanation. In addition, critics claimed that it was impossible to experimentally test the Gaia hypothesis. Finally, scientists reject the idea that Gaia is a living organism because the planet is not able to reproduce, a characteristic considered basic to life.

Lovelock argued against the claim that the Gaia hypothesis was teleological. He stated that he never attributed purpose or consciousness to the feedback mechanisms that regulate the planet. In 1983, Lovelock developed a mathematical model called Daisyworld that demonstrated how feedback loops could occur without any intent. In the model, both black and white daisies inhabit a planet. Light daisies reflect light, cooling the planet, and dark daisies absorb light, warming the planet. The daisies' growth depends on the temperature of the planet. When the model is run and the sun is allowed to change its temperature, the populations of the two kinds of daisies respond in a way that keeps the temperature optimal for their growth. Although the species in Daisyworld live by rules that only concern their own survival, self-regulation of the planet is an emergent property of the system.

In 1988, the American Geophysical Union organized an entire conference to discuss the Gaia hypothesis. The compelling arguments of the Daisyworld model defeated much of the early criticisms of the Gaia hypothesis. At the conference, physicist and philosopher James Kirchner expanded the Gaia hypothesis to encompass a variety of different theories. For example, Strong Gaia Theory, also called Optimizing Gaia Theory, claims that the living parts of the environment actively control the physical environment to optimize conditions for itself. On the other hand, Influential Gaia Theory gives much less influence to the biota. It states that living components influence only certain aspects of the environment, like the temperature and the atmosphere.

Although it was received critically, the Gaia hypothesis has won over most of its initial detractors and become a fundamental part of ecological science. The field of geophysiology spun out of the Gaia hypothesis, which compares the systems of the planet to those of an individual organism, with the rivers and oceans acting as veins and arteries and the atmosphere acting as a lung. Most ecologists now recognize the planet as a super ecosystem and agree that studying global ecology is key to understanding the impacts of humans on the planet.