The last half of this century witnessed incredible leaps in our understanding of planet Earth. Beyond the technological achievements, these decades have produced a substantial body of evidence in support of a revolutionary hypothesis, first posed by Alfred Wegener in the early 1900s, that the continents move around the planet, like ice cubes in a glass. The theory of plate tectonics, as it is now known, embodies a century or more of scientific research, bringing together the efforts of oceanographers, geophysicists, climatologists, palenotologists and more. It represents to my mind what the scientific method is all about and provides an awesome example of how science works.
Another example of how science works is a revolutionary hypothesis first proposed by an atmospheric chemist the the late 70s. This hypothesis, known as the Gaia Hypothesis, states that the Earth is alive. While perhaps agreeable to many an artistic or spiritual soul, the very statement of the hypothesis rankled some scientists. Still, two decades later, the Gaia Hypothesis is still with us.
Whether the Gaia Hypothesis will stand the test of time is uncertain. But its impact on how we think of our planet, how we view the processes that create our atmosphere and climate and oceans and even the mountains is unmistakable.
I think you will find it fascinating. Herein is described one of the more controversial scientific hypotheses of our time, the Gaia Hypothesis.
The Gaia Hypothesis proposes that our planet functions as a single organism that maintains conditions necessary for its survival. Formulated by James Lovelock in the mid-1960s and published in a book in 1979, this controversial idea has spawned several interesting ideas and many new areas of research. While this hypothesis is by no means substantiated, it provides many useful lessons about the interaction of physical, chemical, geological, and biological processes on Earth. Thus, it is a good starting point for our study of oceanography, providing a broad overview of the kinds of processes that will interest us throughout the semester.
Throughout history, the concept of Mother Earth has been a part of human culture in one form or another. Everybody has heard of Mother Earth, but have you ever stopped to think who (or what) Mother Earth is? Consider these explanations.
The Hopi name for Mother Earth is Tapuat (meaning mother and child), symbolized by a form of concentric circles or squares, as shown below. These forms symbolize the cycle of life, the rebirth of the spirit, its earthly path, and, possibly, its return to the spiritual domain. The lines and passages within the "maze" represent the universal plan of the Creator and the path that man must follow to seek enlightenment.
A more imposing definition of Mother Earth might be found in the Hindu goddess Kali. She is the Cosmic Power, representing all of the good and all of the bad in the Universe, combining the absolute power of destruction with the precious motherly gift of creation. It is said that Kali creates, preserves, destroys. Also known as the Black One, her name means "The Ferry across the Ocean of Existence."
The ancient Greeks called their Earth goddess Ge or Gaia. Gaia embodies the idea of a Mother Earth, the source of the living and non-living entities that make up the Earth. Like Kali, Gaia was gentle, feminine and nurturing, but also ruthlessly cruel to any who crossed her. Note that the prefix "ge" in the words geology and geography is taken from the Greek root for Earth.
James Lovelock has taken the idea of Mother Earth one step further and given it a modern scientific twist. (Are our modern Mother Earth "hypotheses" any more refined than ancient Mother Earth myths?). Lovelock defines Gaia "as a complex entity involving the Earth's biosphere, atmosphere, oceans, and soil; the totality constituting a feedback or cybernetic system which seeks an optimal physical and chemical environment for life on this planet." Through Gaia, the Earth sustains a kind of homeostasis, the maintenance of relatively constant conditions.
The truly startling component of the Gaia hypothesis is the idea that the Earth is a single living entity. This idea is certainly not new. James Hutton (1726-1797), the father of geology, once described the Earth as a kind of superorganism. And right before Lovelock, Lewis Thomas, a medical doctor and skilled writer, penned these words in his famous collection of essays, The Lives of a Cell:
Viewed from the distance of the moon, the astonishing thing about the earth, catching the breath, is that it is alive. The photographs show the dry, pounded surface of the moon in the foreground, dry as an old bone. Aloft, floating free beneath the moist, gleaming, membrane of bright blue sky, is the rising earth, the only exuberant thing in this part of the cosmos. If you could look long enough, you would see the swirling of the great drifts of white cloud, covering and uncovering the half-hidden masses of land. If you had been looking for a very long, geologic time, you could have seen the continents themselves in motion, drifting apart on their crustal plates, held afloat by the fire beneath. It has the organized, self-contained look of a live creature, full of information, marvelously skilled in handling the sun.
Thomas goes even one step further when he writes: "I have been trying to think of the earth as a kind of organism, but it is a no go...it is most like a single cell."
Whether the Earth is a cell, an organism, or a superorganism is largely a matter of semantics, and a topic that I will leave to the more philosophically minded. The key point here is the hypothesis that the Earth acts as a single system - it is a coherent, self-regulated, assemblage of physical, chemical, geological, and biological forces that interact to maintain a unified whole balanced between the input of energy from the sun and the thermal sink of energy into space.
In its most basic configuration, the Earth acts to regulate flows of energy and recycling of materials. The input of energy from the sun occurs at a constant rate and for all practical purposes is unlimited. This energy is captured by the Earth as heat or photosynthetic processes, and returned to space as long-wave radiation. On the other hand, the mass of the Earth, its material possessions, are limited (except for the occasional input of mass provided as meteors strike the planet). Thus, while energy flows through the Earth (sun to Earth to space), matter cycles within the Earth.
The idea of the Earth acting as a single system as put forth in the Gaia hypothesis has stimulated a new awareness of the connectedness of all things on our planet and the impact that man has on global processes. No longer can we think of separate components or parts of the Earth as distinct. No longer can we think of man's actions in one part of the planet as independent. Everything that happens on the planet - the deforestation/reforestation of trees, the increase/decrease of emissions of carbon dioxide, the removal or planting of croplands - all have an affect on our planet. The most difficult part of this idea is how to qualify these effects, i.e. to determine whether these effects are positive or negative. If the Earth is indeed self-regulating, then it will adjust to the impacts of man. However, as we will see, these adjustments may act to exclude man, much as the introduction of oxygen into the atmosphere by photosynthetic bacteria acted to exclude anaerobic bacteria. This is the crux of the Gaia hypothesis.
James Lovelock, in collaboration with another eminent scientist, the microbiologist Lynn Margulis, first explained the Gaia hypothesis as such: "Life, or the biosphere, regulates or maintains the climate and the atmospheric composition at an optimum for itself." Inherent in this explanation is the idea that biosphere, the atmosphere, the lithosphere and the hydrosphere are in some kind of balance -- that they maintain a homeostatic condition. This homeostasis is much like the internal maintenance of our own bodies; processes within our body insure a constant temperature, blood pH, electrochemical balance, etc. The inner workings of Gaia, therefore, can be viewed as a study of the physiology of the Earth, where the oceans and rivers are the Earth's blood, the atmosphere is the Earth's lungs, the land is the Earth's bones, and the living organisms are the Earth's senses. Lovelock calls this the science of geophysiology - the physiology of the Earth (or any other planet).
Viewed from this angle, there are certain predictions and experiments that can be performed to refute or lend evidence to the Gaia hypothesis. In fact, it was the search for life on Mars that led to Lovelock's early ideas about the existence of Gaia. As part of a NASA team formed in 1965 to look for life on other planets, Lovelock was asked to propose hypotheses that would demonstrate whether life existed on a planet or not. One of these hypotheses was the idea that gases in an atmosphere on a "dead" planet would be in chemical equilibrium, that is, all the possible chemical reactions that could have happened would have happened and the gases of the atmosphere would be relatively inert. On the other hand, if life existed on the planet, gases in the atmosphere would not be in balance, and chemical reactions would be actively occurring.
|N (<2%) CO2 (95%)
|N (77%), CO2( 0.03%)
atmosphere not in
N (<3%) CO2 (95%)
When they looked at the gaseous composition of Mars and Venus, they saw that the atmosphere was largely composed of the generally unreactive gas carbon dioxide. According to their hypothesis, both these planets would be dead. However, when they looked at Earth, they saw that the atmosphere was an unusual and unstable mixture of many gases. Thus, life was expected to be present on Earth (which we all know is true).
While perhaps not so dramatic, this example should give you some idea of how science works and how the Gaia hypothesis came into being (see handout). The fact that the gaseous composition of the Earth was not in chemical equilibrium, yet appeared to be maintained in a constant state, suggested some form of planetary regulation for the planet's atmosphere. Lovelock initially suggested that life itself maintained the composition of the atmosphere, but has broadened the concept to include the whole system of the climate, the rocks, the air, and the oceans as a self-regulating process.
To understand how the Earth might be living, let's take a look at what defines life. Physicists define life as a system of locally reduced entropy (life is the battle against entropy). Molecular biologists view life as replicating strands of DNA that compete for survival and evolve to optimize their survival in changing surroundings. Physiologists might view life as a biochemical system that us able to use energy from external sources to grow and reproduce. According to Lovelock, the geophysiologist sees life as a system open to the flux of matter and energy but that maintains an internal steady-state.
[updated 1999] Modern biology texts often provide the best descriptions of what defines like. Before you proceed, take a few moments to review the characteristics of living matter that I have summarized on a separate page. Read Characteristics of Living Matter here.
Redwood trees from the
National and State Parks
Electronic Visitor's Center
One useful analogy that has been proposed for understanding Gaia is the California redwood tree, Sequoia gigantea. These trees which stand in great groves along the northern coast of California and elsewhere can stand as high as 300 feet and weigh as much as 2000 tons. Some of them are more than 3000 years old.
Redwood trees are like Gaia because 97% of their tissues are dead. The wood of the trunk and the bark of the tree are dead. Only a small rim of cells along the periphery of the trunk is living. The trunk of the tree is similar to the Earth's lithosphere with a thin layer of living organisms spread across its surface. The bark, like the atmosphere, protects the living tissues, and allows for the exchange of biologically important gases, such as carbon dioxide and oxygen.
There is no doubt in my mind that a redwood tree is a living entity. Would you just call the outer layer the redwood tree and the rest of it dead wood? The same holds true for Gaia. While much of the Earth may be considered "non-living", the fact that all of these non-living parts are involved to some extent in living processes suggests that the whole Earth is alive, just like a redwood tree.
To better understand how the Earth functions physiologically, let's look at one example that has recently been proposed as evidence of Gaia. Let's compare mechanisms of temperature regulation in our bodies and on Earth.
All of us know that our body temperatures are maintained pretty close to 98.6 degrees F (37 degrees C). The maintenance of this body temperature is the result of feedbacks between the brain and various organs and systems of the body. Our bodies have developed different responses to increases or decreases in our core temperature. If it is too cold, our bodies produce heat by shivering; if it is too warm, our bodies sweat and remove heat through evaporation. Of course, humans have extended their ability to survive in extremes of temperatures by inventing clothing that insulates, heats, and even cools our bodies. Such clothing has allowed humans to explore the coldest waters of the polar oceans or the hottest regions of the world's deserts.
On Earth, temperature is regulated in a similar, albeit, more complicated fashion. We will examine how the sun warms the Earth in more detail in a later lecture, but for now we can gain some understanding by just considering the effects of the Earth's albedo. Albedo refers to the color of a planet and its ability to absorb or reflect light. Probably most of you have experienced the difference in temperature between a black asphalt street and a white sidewalk; the Earth's temperature regulation works in much the same way. Dark areas, such as mountains in summer, forests, or even the ocean, tend to absorb heat energy from the sun. Light areas, such as deserts, cloudy areas, or the polar ice caps tend to reflect the sun's energy away from the Earth.
As you can imagine, the albedo of the Earth is not constant. What kinds of changes occur over the Earth's surface that would affect the Earth's albedo?
One possible means by which global temperature is regulated is by clouds. If there are more clouds, more sunlight is reflected away from the earth, and the earth cools. If there are less clouds, more sunlight is able to reach the surface of the Earth and the earth warms. What factors control the abundance of clouds?
There are many factors that affect cloud cover over the planet. The interaction of the atmosphere with the ocean is one major factor. Think of how fog forms along the coast during early summer and you'll get the idea. Other factors, such as the rain shadow effect and weather fronts contribute to cloud cover over the planet.
Given that the oceans cover two-thirds of the Earth's surface, it stands to reason that anything that contributes to the formation of clouds over the ocean will have a major impact on the Earth's temperature. One such mechanism proposed in the last couple decades is the release of cloud-condensation nuclei (or CCN's) by marine phytoplankton, particularly coccolithophorids. Coccolithophorids are well-known for their beautiful calcareous skeletons that make up the White Cliffs of Dover in England.
sp, one of many species of
coccolithophorids living in the ocean
Clouds form when water vapor in the atmosphere condenses or freezes. However, for clouds to form, a particle or "nucleus" must be present to "gather up" the water into a droplet. These particles, called cloud-condensation nuclei, are the tiny particles in the atmosphere that lead to the formation of clouds. Water vapor condenses around these particles and clouds are formed.
One substance that can act as a CCN is dimethyl sulphide, or DMS. It has been known for quite some time that certain algae or phytoplankton (plant plankton that live in the ocean) release trace quantities of DMS. Production of DMS by phytoplankton may be sufficient to cause the formation of clouds, and recent research has been directed towards quantifying the amounts of DMS released into the atmosphere by organisms living in the sea.
Where this process becomes interesting for Gaia is the possibility that phytoplankton can control the temperature of the Earth by regulating the amount of cloud cover over the oceans. Imagine that! Phytoplankton, tiny single-celled plants in the sea, have their fingers on the Earth's thermostat! When the sun is shining brightly, phytoplankton grow rapidly (they're plants, remember?) and produce DMS, which leads to clouds. After a while, the increase in clouds lowers the temperature of the Earth, but it also blocks the sunlight to the phytoplankton. As a result, the phytoplankton grow more slowly, less clouds are formed, and the temperature of the Earth rises. The cycle continues to repeat in a self-regulating and balanced manner.
While much more research is needed, there is some evidence that phytoplankton could control the formation of clouds and the Earth's temperature to some degree. Regardless of whether this mechanism bears the test of time, it does give us pause to think of how living organisms and the Earth itself may interact with each other. It should make us sit and wonder how such a mechanism evolved. For sure, the idea that the whole Earth - the lithosphere, atmosphere, hydrosphere, and biosphere - works together in a harmonious fashion has great intellectual, philosophical, and poetical appeal, if nothing else!
If indeed the Earth is a living organism and the sum of its biological, geological, chemical, and hydrological processes act in concert, what then might we expect of such an organism? How should such an organism act?
We've already mentioned the maintenance of non-equilibrium conditions in the atmosphere as one characteristic of a Gaian planet. We also looked at how organisms such as phytoplankton can transfer chemicals such as DMS into the atmosphere and thus, participate in the cycling of elements within the planet. Organisms are a vital part of all chemical cycles and I would like to introduce to you here the concept of biogeochemical cycles.
By their very nature (and as the name implies) biogeochemical cycles are a mechanism by which the Earth's elements are transformed and carried (in the physical sense) around the Earth. Because the Earth's mass (and material elements) are fixed, the Earth must recycle elements to make them available for other processes. Otherwise, the whole system would run down and the Earth would be just like the moon.
The most common biogeochemical cycles are the carbon cycle, the nitrogen cycle, and the sulfur cycle. Living organisms are a vital part of these cycles. Tremendous masses of material are consumed, transformed, transported, and recycled by the actions of living organisms. In fact, the deposition of sediments in shallow waters is responsible for the uplifting of coastal shores.
Planetary processes governed by living organisms lend credence to the Gaia hypothesis, but they do not prove her existence. If, after a number of decades, a large body of evidence develops that supports the hypothesis that our planet is a living, self-regulating organism, then the Gaia hypothesis may be upgraded to a theory, much like the theory of gravity. Until then, Gaia is an idea that stimulates our thinking and generates scientific research that helps us better understand our planet and how it works.
As one last look at what Gaia might predict, I would like to offer an idea of my own. One of the biggest criticisms against the idea that Gaia is a "living" organism is the inability of the planet to reproduce. Certainly one of the hallmarks of living organisms is their ability to replicate and pass on their genetic information to succeeding generations. In the case of Gaia, this does not appear to be true, or does it?
I would like to propose that man himself is the means by which Gaia will reproduce. Man's exploration of space, his interest in colonizing other planets, and the large body of sci-fi literature that describes terraforming, lend strong evidence to the idea that Gaia is planning to reproduce. Imagine that man colonizes another planet. Imagine that the planet slowly begins to transform; the atmosphere changes, perhaps leading to the formation of ice caps; plants grow, creating clouds and changing the planet's albedo. No longer will this planet be a static, forbidden place. It will be transformed into a place of beauty -- a living, breathing, evolving entity. This indeed is the power of Gaia, and one of the more fascinating and compelling reasons to consider her existence!
Finally, beyond the scientific importance of what we have discussed here, we might do well to consider some of the more poetical thoughts of the originator of the theory. At the end of Chapter 1 in his first book, Lovelock writes:
"If Gaia exists, the relationship between her and man, a dominant animal species in the complex living system, and the possibly shifting balance of power between them, are questions of obvious importance...The Gaia hypothesis is for those who like to walk or simply stand and stare, to wonder about the Earth and the life it bears, and to speculate about the consequences of our own presence here. It is an alternative to that pessimistic view which sees nature as a primitive force to be subdued and conquered. It is also an alternative to that equally depressing picture of our planet as a demented spaceship, forever traveling, driverless and purposeless, around an inner circle of the sun."
I first heard of the Gaia Hypothesis as a graduate student at the University of Southern California (USC) in the 1980s. Having taken a couple courses in Systems Ecology from Dr. James Kremer, I was more than accepting of the idea that systems have emergent properties that cannot be discerned from their individual components. Within that context, the Gaia Hypothesis made sense to me, perhaps more philosophical scientific, but sense, nonetheless.
Since the time of writing these notes in the summer of 1996 (just before I started teaching at Fullerton College), I have learned a lot more about the Gaia Hypothesis, both from the WWW and from conversations with Tom Morris, who teaches planetary biology at Fullerton College and hosts the Planetary Biology Home Page. It has also become somewhat of a theme of mine throughout all of my oceanography classes, not so much the hypothesis, but the idea that physical, geological, chemical and biological processes are interdependent, something that fits quite well with Gaian Theory.
Here then are a few more things that I have learned in the past three years that may further elucidate and validate this important idea.
The Many Faces of Gaia
One of the more interesting extensions of the Gaia Hypothesis has been its transformation from one hypothesis to multiple hypotheses. This is not uncommon in scientific work and it generally represents a healthy and lively application of the scientific method. This divergence of views arises as a result of the different approaches of individual scientists and their beliefs, in the sense of their view of what a body of evidence supports or doesn't support.
Recognition of the many Gaia hypotheses evolved from a symposium on the Gaia Hypothesis held in 1988. A group of geophysicists and others came together to discuss the hypothesis, an event in itself that helped fuel its acceptance. While there were (and still are) many detractors, Gaia did appear to gain a toehold with general acceptance of the idea that life at least influences planetary processes.
Certainly no one could argue against the evidence that dramatic changes occurred in Earth's early atmosphere as a result of the evolution of photosynthetic organisms approximately 3.5 billion years ago. The resulting oxygen holocaust, which established present-day oxygen concentrations about 2.5 billion years ago, radically changed physical, geological, chemical and biological processes on our planet. Rust is one good example of chemical alterations brought about by oxygen. A good biological example is the appearance of oxygen-breathing organisms, or aerobes, and the confinement (in a figurative sense) of non-oxygen breathing organisms, or anaerobes, to swamps and bogs and places deep in the Earth.
The idea that life influences planetary processes (i.e. has a substantial effect on abiotic processes) has become known as the weak (or influential) Gaia hypothesis. This hypothesis is generally supported by scientists today and, in fact, is probably most responsible for stimulating continued research on Gaia. Even the most conservative scientists agree that research on the way in which living organisms interact with non-living processes may yield useful information. Much of our modern-day climate research is based, to some degree, on this idea.
As a result of defining a weak Gaia hypothesis, the original Gaia hypothesis (i.e. that life controls planetary processes) became known as the strong (or optimizing) Gaia hypothesis. Few scientists are willing to support this hypothesis.
One of the reasons that the Gaia Hypothesis sparked such debate in scientific circles has to do with scientists' ability to test hypotheses. As we learned earlier, the traditional scientific method relies on refuting a hypothesis, proving it wrong, as the means for eliminating possible explanations. This method of falsifying a hypothesis was proposed by the Austrian-born Karl Popper in a 1934 publication called Logik Der Forschung or The Logic of Scientific Discovery. (Popper passed away in 1994 but he is still considered one of the most influential philosophers of the 20th Century. You can learn more about him by visiting the Karl Popper Web, http://www.eeng.dcu.ie/~tkpw/.) The single largest complaint lodged against the strong Gaia hypothesis is that experiments can't be designed to refute it (or test it at all, for that matter.)
Without going into all the details, suffice it to say that those arguments are valid. The strong Gaia hypotheis states that life creates conditions on Earth to suit itself. Life created the planet Earth, not the other way around. As we explore the solar system and galaxies beyond, it may one day be possible to design an experiment to test whether life indeed manipulates planetary processes for its own purposes or whether life is just an evolutionary processes that occurs in response to changes in the non-living world.
For an excellent account of the scientific evidence and controversies and much greater detail than I have provided here, check out these web sites dedicated to the Gaia Hypothesis.
The Gaia Hypothesis
The Gaia Hypothesis
To read more about the Gaia Hypothesis and related topics, check out these publications:
J. E. Lovelock, Gaia: A New Look at Life on Earth, Oxford University
James Lovelock, Healing Gaia: Practical Medicine for the Planet, Harmony Books, 1991;
Lewis Thomas, The Lives of a Cell, Bantam Books, 1974.
The Gaia hypothesis: can it be tested? in Reviews of Geophysics 27:2, 223-235, 1989