Geology Reference
In-Depth Information
of the supernova explosion which led to Gaia (calcium, carbon and oxygen), the most
common form of which is
calcite
. Calcite can itself manifests in a variety of ways, but
is most commonly encountered as light porous chalk, or as the much denser limestone.
Emiliania
is a single-celled photosynthesiser, and is a master of using the energy of the
sun to convert carbon dioxide and water into sugars and oxygen. But she is also skilled
in another complex biochemical art—the precipitation of calcite within deep intracellu-
lar chambers into exquisitely crafted coccoliths, which, when complete, are excreted to
surround the cell in a white coating of chalky plates. Chemists write down the formula
for calcium carbonate (the chalky stone berries carried by these little creatures) as fol-
lows:
CaCO
3
This means that a single molecule of chalk contains one atom of calcium, one atom of
carbon and three atoms of oxygen. As we shall soon discover, it is the presence of the
carbon atom which gives chalk its significance for Gaia's long-term temperature regula-
tion.
Now let's move from the micro-scale of the story to the far vaster spatial scale in-
volving movements of the Earth's crust and the immensely powerful activity of volca-
noes, which spew out carbon dioxide—the greenhouse gas—along with large quantities
of lava, a kind of rock closely related to basalt and granite. Basalt is the mother of all
rocks. It wells up at Gaia's mid-oceanic ridges, hot and pliable like just melting chocol-
ate from deep inside the Earth. Granite is born at super-high temperatures and pressures
deep below the continental margins when basalt is cooked with water, or when calcite
and silica deposits re-combine. Basalt and granite (known to scientists as calcium silic-
ate rocks) contain a lot of calcium, oxygen and silicon which self-organise on cooling
into three-dimensional crystalline lattices of exquisite precision and regularity. Locked
up in the rock lattice like captive princesses in an ancient castle are positively charged
calcium ions which, never losing hope of experiencing something other than the stasis
of a crystalline existence, long to escape the lattice prison that has held them captive for
often millions of years. There is only one way that calcium's escape can be assured—she
must embark on a chemical marriage with carbon, her prince, suitor and bridegroom
who, riding the atmosphere as part of a carbon dioxide molecule, searches everywhere
for his rock-incarcerated princess. When a carbon dioxide molecule finally encounters
basalt or granite the marriage can at last happen, but only after some complex challenges
have been overcome.
First, a water molecule from a rain shower must dissolve a carbon dioxide molecule
to yield carbonic acid that immediately dissociates into two new chemical beings: a bi-
carbonate ion, in which the carbon atom is linked to one hydrogen and three oxygen
