Introduction / 7large amounts of nitrogen and oxygen, as well as methane, which cannot survive
for long in the presence of oxygen. It then occurred to him that the environmental
modifications made and sustained by living organisms actually produced and
maintained chemical and physical conditions optimum for those organisms
themselves. In other words, the organisms produce an environment which
suits them and then ‘manage’ the planet in ways that maintain those conditions.Does this suggest that our climate is moderated, or even controlled, by biological manipulation?
Certainly this is the view of James Lovelock, whose Gaia hypothesis takes the idea much further,
suggesting that the Earth may be regarded as, or perhaps really is, a single living organism. It was
this idea of a ‘living planet’ that he came to call ‘Gaia’ (LOVELOCK, 1979).
His hypothesis has aroused considerable interest, but Gaia remains controversial and there are serious
objections to it. Expressed in its most extreme form, which is that almost all surface processes are
biologically driven, it appears circular, with an explanation for everything, as when the existence of
Gaia is introduced to explain the hospitable environment and the hospitable environment proves the
existence of Gaia (JOSEPH, 1990). On the other hand, the more moderate version, which emphasizes
the biological component of biogeochemical cycles more strongly than most traditional accounts,
commands respect and promises to be useful in interpreting environmental phenomena, although not
all scientists would associate this with the name ‘Gaia’ (WESTBROEK, 1992). It has been found,
for example, that the growth of marine plankton can be stimulated by augmenting the supply of iron,
an essential and, for them, limiting nutrient, with implications for the rate at which carbon dioxide is
transferred from the atmosphere to the oceans and, therefore, for possible climate change (DE BAAR
ET AL., 1995).
Authorities differ in the importance they allot to the role of the biota (the total of all living organisms
in the world or some defined part of it) in driving the biogeochemical cycles, but all agree that it is
great, and it is self-evident that the constituents of the biota shape their environment to a considerable
extent. Grasslands are maintained by grazing herbivores, which destroy seedlings by eating or
trampling them, so preventing the establishment of trees, and over-grazing can reduce semi-arid land
to desert. The presence of gaseous oxygen in the atmosphere is believed to result from photosynthesis.
We alter the environment by the mere fact of our existence. By eating, excreting, and breathing we
interact chemically with our surroundings and thereby change them. We take and use materials,
moving them from place to place and altering their form. Thus we subtly modify environmental
conditions in ways that favour some species above others. In our concern that our environmental
modifications are now proceeding on such a scale as to be unduly harmful to other species and
possibly ourselves, we should not forget that in this respect we differ from other species only in
degree. All living things alter their surroundings, through their participation in the cycles that together
comprise the system which is the dynamic Earth.
3. Ecology and environmentalism
Our concern over the condition of the natural environment has led to the introduction of a new concept,
of ‘environmental quality’, which can be measured against defined parameters. To give one example, if
the air contains more than 0.1 parts per million (ppm) of nitrogen dioxide (NO 2 ) or sulphur dioxide