by David Orrell
Here is a brief introduction to Gaia theory, as developed by
Lovelock, Margulis and others.
In the early 1960ís,
James Lovelock was invited by NASA to
participate in the scientific research for evidence of life on Mars.
His job was to design instruments, capable of detecting the presence
of life, which could be sent on a spacecraft to Mars. This wasnít
straightforward, since it was hard to know what to test for: any
life forms on Mars may be radically different from those on Earth.
This led him to think about what constitutes life, and how it can be
detected. He decided that the most general characteristic of life
was that it takes in energy and matter and discards waste products.
He also reasoned that organisms would use the planetís atmosphere as
a medium for this cyclic exchange, just as we breathe in oxygen and
expel carbon dioxide. He speculated that life would therefore leave
a detectable chemical signature on the Martian atmosphere. Maybe it
could be detected from Earth, so it wouldnít even be necessary to
send a spaceship.
To test his idea, he and a colleague, Dian Hitchcock, began to
analyze the chemical makeup of Mars, and compare it with that of the
Earth. The results showed a strong contrast. The atmosphere of Mars,
like Venus, was about 95% carbon dioxide, with some oxygen and no
methane. The Earth was 77% nitrogen, 21% oxygen, and a relatively
large amount of methane. Mars was chemically dead; all the reactions
that were going to take place had already done so. The Earth,
however, was far from chemical equilibrium. For example, methane and
oxygen will react with each other very easily, and yet they are both
present in the atmosphere. Lovelock concluded that for this to be
the case the gases must be in constant circulation, and that the
pump driving this circulation was life.
Lovelock began to look back at the history of lifeís interaction
with the atmosphere. He noted that about three billion years ago,
bacteria and photosynthetic algae started to remove carbon dioxide
from the atmosphere, producing oxygen as a waste product. Over
enormous time periods, this process changed the chemical content of
the atmosphere - to the point where organisms began to suffer from
oxygen poisoning! The situation was only relieved with the advent of
organisms powered by aerobic consumption.
life processes, the cumulative actions of countless
organisms, that were controlling the atmosphere. And viewed from
outer space, the mass effect of these processes was that the Earth
itself appeared as a living entity - especially in comparison with
its dead neighbors. Lovelock had a sudden realization that the
Earth could best be described as a kind of super-organism:
"For me, the personal revelation of
Gaia came quite suddenly - like
a flash of enlightenment. I was in a small room on the top floor of
a building at the Jet Propulsion Laboratory in Pasadena, California.
It was the autumn of 1965 ... and I was talking with a colleague,
Dian Hitchcock, about a paper we were preparing ... It was at that
moment that I glimpsed Gaia. An awesome thought came to me. The
Earthís atmosphere was an extraordinary and unstable mixture of
gases, yet I knew that it was constant in composition over quite
long periods of time. Could it be that life on Earth not only made
the atmosphere, but also regulated it - keeping it at a constant
composition, and at a level favorable for organisms?" (1991)
On a stroll with his novelist
neighbor William Golding, Lovelock
described his idea, and asked advice for a name. Golding suggested
Gaia, after the Greek Earth Goddess. The Gaia Hypothesis was born.
In 1979, Lovelock wrote the book "Gaia: A New Look at Life on
Earth", which developed his ideas. He stated 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. This is in
contrast to the conventional wisdom which held that life adapted to
the planetary conditions as it and they evolved their separate
Key to Lovelockís idea was his observation that
the planet is
self-regulating. He knew, for example, that the heat of the sun has
increased by 25% since life began on Earth, yet the temperature has
remained more or less constant. However he didnít know precisely
what mechanisms were behind the regulation. It was when he began to
collaborate with the American microbiologist Lynn Margulis that the
full theory began to take shape. Margulis was studying the processes
by which living organisms produce and remove gases from the
atmosphere. In particular she was examining the role of microbes
which live in the Earthís soil. Working together, they
managed to uncover a number of feedback loops which could act as
An example is the carbon dioxide cycle. Volcanoes constantly produce
massive quantities of carbon dioxide. Since carbon dioxide is a
greenhouse gas, it tends to warm the planet. If left unchecked, it
would make the Earth too warm to support life. While plants and
animals take in and expel carbon dioxide through life processes such
as photosynthesis, respiration and decay, these processes remain in
balance and donít affect the net amount of the gas. Therefore there
must be another mechanism.
One process by which carbon dioxide is removed from the atmosphere
is rock weathering, where rainwater and carbon dioxide combine with
rocks to form carbonates. Lovelock, Margulis and others discovered
that the process is greatly accelerated by the presence of soil
bacteria. The carbonates are washed away into the ocean, where
microscopic algae use them to make tiny shells. When the algae die,
their shells sink to the bottom of the ocean, forming limestone
sediments. Limestone is so heavy that it gradually sinks underneath
the Earthís mantle, where it melts. Eventually some of the carbon
dioxide contained in the limestone will be fed back into the
atmosphere through another volcano.
Since the soil bacteria are more active in high temperatures, the
removal of carbon dioxide is accelerated when the planet is hot.
This has the effect of cooling the planet. Therefore the whole
massive cycle forms a feedback loop. Lovelock and Margulis
identified a number of other feedback loops which operate in a
similar way. An interesting feature of these loops is that, like the
carbon dioxide cycle, they often combine living and non-living
The importance of biological processes on the planet was pointed out
by the Russian scientist Vernadsky, who as early as 1929 said:
"Life appears as a great, permanent and continuous infringer on the
chemical ídead-hardnessí of our planetís surface ... Life therefore
is not an external and accidental development on the terrestrial
surface. Rather, it is intimately related to the constitution of the
Earthís crust, forms part of its mechanism, and performs in this
mechanism functions of paramount importance, without which it would
not be able to exist." (1929)
Vernadsky showed, for example, that living organisms are the primary
transformer of solar energy to chemical energy, and stressed the
importance of biotransport systems. An example of a biotransport
system is birds which feed on marine life, hence transferring an
enormous amount of matter from the oceans back to the land. In order
to understand how the planet works, one has to take into account the
effect of life - exactly what Lovelock says.
Gaia Hypothesis immediately created a lot of interest. The idea
that the Earth was alive had been expressed several times before,
but it gained special resonance in the early 60ís because of the
space flights which allowed the Earth to be viewed for the first
time as a complete entity from outer space. In a way these
photographs were to the Gaia idea what computers were to chaos
theory; they allowed one to see what was going on, and therefore
brought the subject alive to a great many people.
The intellectual climate was also becoming amenable. A lot of work
was being done at that time on self-organizing systems. Ilya
Prirogine had been studying systems far from thermal or chemical
equilibrium which nevertheless showed a high degree of order, for
example the Belousov-Zhabotinskii reaction which produces amazing
periodic oscillations. He realized that there was a close
association between self-organization at states far from
equilibrium, and the nonlinearity of the system. This tied in well
with Lovelockís observation that the Earth is chemically far from
equilibrium, and the nonlinearity of the feedback loops such as the
carbon dioxide cycle.
Meanwhile the Chilean neuroscientists Maturana and Varela were
developing their autopoietic (literally self-making) definition of
life. There is no single definition of life that is accepted by all
fields, however one of the most successful has been their
definition, which states that living beings produce, by their own
rules, the components, including their own boundary, that specify it
and realize it as a concrete unit in space and time (Maturana and
Varela 1987). What is important in this definition is not so much
the material structure of life as the process, organization and set
of relations between the components. Life is a network which
constantly makes itself. The simplest autopoietic
system is the
living cell. For something to be alive by this definition, there is
no requirement that it grow or reproduce or pass on DNA. Since, as
Vernadsky observed, 99.9% of the different molecules on
been created in the life process of Earth, the Earth
would seem to
qualify as a self-making organism.
While the Gaia Hypothesis attracted a lot of interest, it also
received a great deal of criticism. Lovelock had attached great
weight to the idea that the Earth seemed to regulate itself. Some
took this to imply that the Earth was behaving with a sense of
purpose, that it was a teleological being.
Teleology, from the Greek word telos (purpose), asserts that there
is an element of purpose or design behind the workings of nature. It
is part of a very old debate between mechanists who believe that
nature essentially behaves like a machine, and vitalists who believe
there is a non-causal life force. Critics thought Lovelock was
saying that the planet had a life force which was actively
controlling the climate and so on. However this wasnít Lovelockís
intention. He stated that,
íNeither Lynn Margulis nor I have ever
proposed that planetary self-regulation is purposeful ... Yet we
have met persistent, almost dogmatic, criticism that our hypothesis
is teleological.í (1991)
Another loudly voiced objection was that
Gaia had evolved without
any recourse to natural selection - an impossibility, according to
the Darwinists. If the Earth is alive, where is its Selfish Gene,
and who will it pass it onto?
As a response to these criticisms, Lovelock, together with Andrew
Watson, developed the Daisyworld model - an imaginary planet, which
maintains conditions for its survival simply by following its own
natural processes. This simple model has since become an integral
part of the debate about the Gaia Hypothesis.
The Daisyworld planet contains only two species of life:
daisies and dark daisies. Light daisies tend to reflect light, which
has a cooling effect, while dark ones absorb radiation, and
therefore warm the planet. Growth of the daisies depends on the
present population, the natural death rate, the available space and
the temperature (the equations that Lovelock used to model them were
based on the dynamics of real daisy growth). The planet revolves
around a sun, from which it absorbs energy at a rate which depends
on the sunís luminosity and the albedo of the planet. It also
radiates heat out to the universe, at a rate determined by the
Interestingly, when the model is run with the sunís luminosity
gradually increasing, the population of the light and dark daisies
adjust themselves naturally so as to keep the temperature constant
at the optimal level for daisy growth. Daisyworld is an
example of a
self-regulating system. Feedback loops between the daisies and the
planet temperature, contained in the equations relating growth rate
to albedo, somehow conspire to maintain the conditions suitable for
Daisyworld is only a kind of thought experiment, but demonstrates
the principle of self-regulation very convincingly. Itís a viable
ecosystem which regulates its temperature, without any recourse to
selection or teleology.
One of the main ideas to come out of the Daisyworld model is that
the species in an ecosystem can be concerned with nothing more than
their own survival, yet as a consequence of their actions they help
not only themselves but the whole system. We could say that the
self-regulation is an emergent property of the system. There isnít
any need for the white and black daisies to get together and agree
quotas for each otherís populations, and fix growth rates and argue
over how much land should be left uncovered. They just do their own
thing and the planet takes care of itself. All that is needed is
that the daisies give positive and negative feedback to the
temperature, and they are happiest at a particular temperature, so
they tend to keep the planet around that temperature. They make the
planet suit them. Daisyworld addresses the dichotomy that exists
between the reductionist approach, which attempts to understand
systems by breaking them down to their smallest components, and the
holistic approach which views systems as complete entities that must
be understood in their entirety.
A consequence of the Daisyworld model is that it has opened peopleís
eyes to similar systems. An example is the salinity of the oceans,
as described by Hinkle [see Bunyard, 1996]. Living organisms
maintain a salinity which is roughly equal to that of the oceans.
Previously it was thought that this was because natural selection
tended to assist those organisms which were in balance with their
surroundings. The question remained, why has the ocean managed to
maintain a constant level of salinity? The oceanís present salinity
is around 3.4%. If it were to go much above 4%, then basic cell
functions such as the maintenance of membrane potential would fail.
There would be mass extinctions of life in the oceans. And yet there
is no evidence of such extinctions in the last 500 million years.
This is quite strange, because salt is constantly being deposited in
the oceans through the weathering of rocks, yet its concentration is
only 10% of saturation levels. Furthermore, there has been a
multitude of cataclysmic events such as meteorite impacts, periods
of glaciations and so on which one might expect to abruptly alter
salinity. Indeed, attempts to model the salinity regulation using
chemistry or physics have failed. So what is regulating the oceans?
From Daisyworld we might predict that the answer is the organisms
that live in the oceans. In fact, bacteria play a particularly
important role in the running of the oceans (as in most life
processes). Although they constitute only 10-40% of the ocean
biomass, their high surface area to volume ratio means that they
make up 70-90% of the biologically active surface area. And they all
pump salt. Looking at the problem from the point of view of Gaia
Theory breaks down the barriers between what we have traditionally
seen as living and non-living systems.
Daisyworld and the Gaia Hypothesis are controversial because they
touch on the definition of what constitutes life. If we think that
life is about the selfish gene, competition, and survival of the
fittest, then it is hard to see where the Earth fits in. However, it
isnít necessary to think that the Earth is alive in order to
appreciate that it is a highly complex system. And, if we say it is
alive, why is that so threatening? No one doubts that plants are
alive, but they donít do anything nearly as complicated as the Earth
Of course, plants are clearly individuals, which go through specific
lifecycles. Paradoxically, the organisms which behave most like the
Earth are the very smallest - the bacteria. They are potentially
immortal, in that they can reproduce for ever. They happily swap
genes back and forth. They tend to form communities, such as
bacterial mats. Viewed as a single superorganism, they run most of
Gaia theory has already had a huge impact on science, and has
changed the way we view our place in the world. By making us more
aware of the damage we are doing to the eco-system, it may also help
us to survive. One of the lessons of Daisyworld is that, due to the
effect known as hysteresis, damage once done is very difficult to
undo. Our experiment with global warming cannot be halted when we
are uncomfortable with the effects; by then it may be too late. And
once a species is extinct, it cannot be restored. We are just one
part of a larger system, and are reliant on that system for our
continued existence. We harm it at our peril.
Abraham, R.H. 1994. Chaos, Gaia, Eros. Harper Collins.
Bunyard, P. 1996. Gaia in Action: Science of the Living Earth.
Lovelock, J.E. 1979. Gala: A New Look at Life on Earth. Oxford
Lovelock, J.E. 1991. Healing Gaia. Harmony Books.
Lovelock, J.E. 1992. A numerical model for biodiversity. Phil.
Trails. R. Soc. Load. B 338: 383-391.
Margulis, L. and Sagan, D. 1997. Slanted Truths: Essays on Gaia,
Evolution and Symbiosis. New York.
Maturana, H.R. and F.J. Varela. 1987. The Tree of Knowledge.
Watson, A.J. and J.E. Lovelock. 1983. Biological homeostasis of the
global environment: the parable of Daisyworld. Tellus 35B:284.
Vernadsky, V.I. 1929. La Biosphere. Felix Alcan.