Geology Reference
In-Depth Information
Figure 5: Gaia's temperature over the last 400,000 years, from the Vostok ice-core data.
Notice that there has been a regular rhythm in the traces of temperature and carbon di-
oxide, like a heartbeat or a pulse, with brief warm periods, such as the one in which our
civilisation has flourished, every 100,000 years. A tiny change in the amount of sunlight
reaching the Earth appears to set the rhythm because of the amplifying effects of com-
plex internal feedbacks. Notice the close coupling between carbon dioxide and temper-
ature, and also another astonishing fact: during each cold period, the amount of carbon
dioxide has never dropped below 180 ppm (parts per million), and has never exceeded
300 ppm during warm periods. Even scientific sceptics now acknowledge that this is
powerful evidence for a self-regulating Earth, for in the absence of tight regulation one
would have expected the maxima and minima to vary much more erratically and unpre-
dictably. Gaia has revealed herself through bubbles of ancient air.
Further powerful evidence for Gaia has come from studying the remains of life in
rocks up to 550 million years old, the period of her history during which there has been
multicellular life with body parts hard enough to be preserved as fossils. The results of
this work are shown in
Figure 6
where one can see five mass extinctions during which
the diversity of life very rapidly declined, sometimes to alarmingly low levels as in the
Permian extinction 250 million years ago, when about 95% of all fossilisable life forms
vanished from the shallow oceans of the Earth.
