Geology Reference
In-Depth Information
fication of weathering because their hugely effective root systems were able to crumble
and dissolve rocks with a speed and efficiency undreamt of by the microbial realm.
Thus, as Gaia has evolved, the diversification amongst her living beings has gone
hand in hand with greater rock-weathering abilities and with more effective draw-down
of carbon dioxide from the atmosphere into chalk and limestone. During this whole
evolutionary dance the relationship between life, rocks, atmosphere and oceans has in-
tensified and deepened like a good marriage, and Gaia has honed and augmented her
skill at regulating her temperature. She has become more exquisitely responsive to both
the sun's increasing brightness and to varying amounts of carbon dioxide released from
volcanoes, much as a musician begins as a promising young player and matures into
an accomplished virtuoso. As time has gone by, more and more players in the form of
newly evolved species have added their voices to Gaia's symphony, so that today her
orchestra burgeons as never before with diverse sounds from a rich variety of players
and their instruments.
But Gaia has not always been able to regulate her temperature smoothly and easily in
the face of the ever-brightening sun. In
Figure 24
the horizontal axis shows time, run-
ning from about 600 million years ago till now, whilst the vertical axis shows Gaia's
corresponding temperature. In the 'sun only' curve, we see how temperature would have
increased as the sun brightened over time had there been a constant amount of carbon di-
oxide in the atmosphere. But this constancy is of course an illusion—it is nothing more
than a mathematical 'static Earth' for the purposes of comparison.
