Geology Reference
In-Depth Information
the system behaves will depend entirely on the quantitative relationships between these
three feedbacks.
Wherever we look in the biological world we find astonishingly complex feedbacks
of this kind, whether it is within the physiology of individual organisms, in the ecolo-
gical interactions within ecosystems, or indeed amongst the interactions between rocks,
atmosphere, oceans and living beings that constitute Gaia. Such complex systems can
behave in unpredictable ways. The precise behaviour will depend not only on which re-
lationships are present, but also on their relative strengths. Invariably, non-linear rela-
tionships will be present, and if so the system will exhibit a range of behaviours, from
predictable to chaotic, but with sufficient complexity even a system with linear rela-
tionships can give rise to all sorts of behaviours. Simply put, in a linear relationship,
a component's response varies in direct proportion to a change it experiences, and in a
non-linear system it doesn't. A good example of non-linearity is the stock market, where
a slight change in consumer confidence can ripple through the system very quickly to
bring about rapid and unexpected change. It is also possible for tipping points to exist, in
which a small disturbance triggers a sudden and unexpected change. Take a pencil and
line it up parallel to the edge of a table, not too far from the edge. Now give the pencil
a slight push towards the edge and nothing dramatic happens—the pencil has moved a
little, and just as you expected, it is still on the table. Now give it another small push,
and another. Again you observe a predictable response. Eventually, of course, another
slight push equal to all the previous ones takes the pencil through a rapid tipping point
as it falls over the edge and into a new 'stable state' on the floor. Non-linear systems
are riddled with tipping points, but often a system is so complex that it is impossible to
know exactly when these will be encountered.
Daisyworld
We are now well prepared to return to Lovelock and his struggle to create a convincing
cybernetic model of a self-regulating planet. On Christmas Day 1981, as Lovelock
pondered his critics' points without conclusion, a strange coincidence happened which
gave him the lead he was looking for. On his desk was an open copy of the journal
Nature
, one of science's most prestigious periodicals. Lovelock was about to put it back
but just happened to glance at the article spread out before his gaze. To his amazement,
it described some straightforward equations for the growth in grasslands and lawns of
the plantain, a common English wild plant. As he contemplated the text a flash of inspir-
ation leapt into his mind. Into his consciousness came a visualisation of a planet with
only two species—light-and dark-petalled daisies—representing the vast biodiversity of
