Geology Reference
In-Depth Information
Chapter 6
Life, Clouds and Gaia
Sulphur and Albedo
So far we have seen how life is profoundly involved in regulating Gaia's temperature
through its impact on the gaseous chemical beings that inhabit her atmosphere. But this
is not the only way that life has contributed to Gaia's emergent ability to maintain a hab-
itable planet—it also has the power to alter her overall shade, or albedo.
Living beings do this in two major ways. One is by releasing chemicals that seed vast
banks of dense white clouds that reflect the sun's energy back to space before it has had a
chance to heat up the Earth's surface. Another is by covering vast areas of land with dark
or light vegetation that respectively absorb or reflect the sun's rays, thereby warming or
cooling the Earth. Until fairly recently, scientists believed that a given ecological commu-
nity simply responded to whatever environmental conditions had been bestowed upon it
by the great 'non-living' forces of the planet, such as plate tectonics, so it came as quite a
shock to them to discover that this is only partially true; for in fact whole ecological com-
munities, both in the ocean and on land, affect their local temperatures simply by altering
their surface albedo, much as the inhabitants of houses in sun-drenched deserts paint their
houses white to keep them pleasantly cool inside.
This unexpected ability of life to alter planetary albedo has to do with the global sul-
phur cycle. Sulphur is essential for life—without it the amino acids that build proteins
cannot be made—but it is very scarce in the soil, and is hence a limiting nutrient for
