Geology Reference
In-Depth Information
the planet pummel and pulverize the rock, releasing nutrients on a scale unknown during
a time of ice. Myriads of phosphorus, iron, silicon, calcium atoms are captured by plant
roots to be sucked up into the growing green biosphere which, in its heedless growth,
draws out more and more carbon dioxide from the atmosphere. But some of the newly
liberated chemical beings manage to avoid the terrestrial green world altogether, and,
tumbling headlong into rivers and thence to the sea, are put to work in the photosyn-
thetic dance of the minuscule phytoplankton that populate the ocean. In time, over thou-
sands of years, Gaia's photosynthetic beings draw out so much carbon dioxide that the
great efflux from the oceans is counteracted and she experiences a brief interglacial with
a maximum carbon dioxide concentration of 280 parts per million.
But this warm state is a rare, transient thing. It cannot last, for the power of photo-
synthesis on land and in the ocean, in their immensity, has taken so much carbon di-
oxide from the air that the emissions from the warm oceans are totally absorbed, and
more. With less carbon dioxide in the atmosphere, Gaia once again begins her descent
into an icy world as the positive feedbacks begin to move the world towards cooling,
aided now by the gradual and subtle lengthening of her orbit. In a cooling world, the
oceans absorb more carbon dioxide, driving temperatures down even further. The boreal
forests retreat, giving ground to the cooling, carbon-hungry peat bogs, covered in winter
by a reflecting blanket of snow. Favoured in the colder world, ice from the far northern
hemisphere begins to spread south again, further chilling the planet with its whiteness.
Although seriously reduced in the high latitudes, the great biotic communities on land
expand in the south-east Asian tropics, where the lowered sea level exposes new terrain
almost as large as Africa. Here rainforests grow, reducing carbon dioxide even more,
whilst carefully garnering precious hordes of phosphorus atoms thanks to their intricate
rock-weathering skills. The ground waters and rivers swell with this newly found miner-
al wealth, and swirl it down to the oceans where thankful phytoplankton bloom in a last
exuberant frenzy of photosynthesis and cloud-seeding. Now the cooling world dries out,
as less water evaporates from the oceans. Great pressure differences between the topics
and the high latitudes stir up strong winds that carry iron-rich dust from the drying land
far out to sea, bringing a further boon of nutrients to the shimmering, temperature-redu-
cing phytoplankton. As the northern ice expands, the global ocean circulation reconfig-
ures itself into its contracted mode, cooling the planet even more. Gaia has drifted into a
comfortable new age of ice, with around 180 parts per million of carbon dioxide in her
atmosphere until, 100,000 years later, the ellipse in her orbit curves her once more into
the right alignment for warming.
The fact that Gaia has switched from ice ages to interglacials on a regular basis might
lead one to think that her climate has remained stable in either of these two states, but
nothing could be further from the truth. Cores of ice from central Greenland are much
