Geology Reference
In-Depth Information
neider, tight coupling between biota and environment does not exist, so there cannot be
an inherent tendency for the emergence of planetary self-regulation.
These criticisms provided a Lovelock with a stimulating irritant that spurred him on
to develop the strikingly original mathematical models of Gaia which we shall presently
explore. But first let us look at the evidence for a self-regulating Earth.
The Evidence for Gaia
There is in fact good scientific evidence that our Earth does indeed have a remarkable
ability for maintaining habitable conditions despite many external and internal forces
that could easily have destroyed life during the course of her 4,600 million (4.6 billion)
year existence. Look carefully at the graph in
Figure 4
, which shows that Gaia's average
temperature has never been too hot or too cold for life, despite some warmer and some
cooler periods. This relatively equable temperature history presents us with a consid-
erable scientific puzzle because of the way in which our sun has evolved and changed
during Gaia's lifetime.
Astrophysicists have established beyond reasonable doubt that our sun has gradually
bathed Gaia with more and more energy over geological time, as more and more hydro-
gen has fused into helium in the sun's deep interior. The sun today is about 25% brighter
than it was around 3,500 million years ago, when life first appeared on the planet, and
yet Gaia's temperature has never been too hot or too cold for life. The data in
Figure 4
come from hard science, and are surely excellent evidence for Gaia. To think that her
relatively stable temperature could have been maintained over such immense periods
purely by luck is tantamount to a highly unscientific belief in miracles. A more rational
attitude would be to accept that the data are strongly suggestive of an innate tendency for
planetary self-regulation, and to then ask how this might have arisen. The fact that Gaia
has been able to maintain habitable conditions despite the external stress of an ever-
brightening sun means that she is indeed in some sense alive, because self-regulation is
a property of all living beings, or of their artefacts. You and I are no different from Gaia,
in that we are able to keep our body temperatures within very narrow limits despite a
wide range of external temperatures. We have an array of methods for doing this, which
operate unconsciously. When it's hot outside we produce sweat, which a passing breeze
evaporates, taking some of our excess heat with it. When it's cold, we redirect blood
flow from the expendable extremities such as fingers and toes to vital internal organs
such as liver and intestines, and we shiver to generate extra warmth.
