Geology Reference
In-Depth Information
Focusing now only on your in-breaths, imagine that carbon dioxide is being
drawn out of the atmosphere by the life-enhanced weathering of the granite in
your hand. Imagine the tree roots, the microbes and the fungi crumbling the rock,
surrounding it with water and carbon dioxide, which is locked up with calcium in
a chalky solution of calcium bicarbonate washed down to the sea to be made into
solid chalk by the coccolithophores. See their chalky shells sinking to the bottom
of the ocean, and visualise vast deposits of chalk and limestone laid down on the
sea bed—the very chalk or limestone that you are holding in your other hand. Be-
come aware of this stone now.
Focusing now only on your out-breaths, see how the chalk sediments are pushed
deep under the Earth when the movements of the Earth's tectonic plates collide
them against a continent. Feel the carbon diox- ide spewing out of volcanoes as
the chalk melts in the intense temperatures and pressures deep down beneath the
continent. As your outbreath stops, you become carbon dioxide coursing through
the atmosphere, warming the Earth.
Feel how, in its melting, the chalk has contributed to the making of new granite.
Connecting once again with the presence of the granite in your hand, repeat the
cycle until it flows naturally and easily.
But what of the brightening sun? Why hasn't its increasingly generous gift of energy
overwhelmed these great negative feedback loops, sending Gaia into an early heat
death? The answer seems to involve life's creative expansion into novelty right from
its first appearance on the planet about 3,500 million years ago. Since those early days
when bacteria were the only life forms, until now, when Gaia teems with a huge vari-
ety of multicellular creatures and hosts a biodiversity greater than ever before, life has
become better and better at weathering rocks and hence at drawing carbon dioxide out
of the air into chalk and limestone. In Gaia's early days, under a cool sun, increasingly
widespread and effective microbial films on granite surfaces carried out the weathering.
In this early phase of her life, Gaia needed an atmosphere which could keep the surface
warm in the face of a cool sun. With only bacteria present on a much smaller continental
area, there was far less weathering of silicate rocks than is the case today. Later, about
2,500 million years ago, when the first nucleated cells spread over the larger continents,
weathering increased. Even later, by about 400 million years ago, under a considerably
brighter sun, there was a need for more effective weathering to remove carbon dioxide
from the atmosphere. The newly evolved land plants provided this much-needed ampli-
