Geology Reference
In-Depth Information
skeletons secreted mostly by coccolithophores. When you look at these cliffs, or indeed
at any other chalk or limestone, you are of course seeing rock, but seen through Gaian
eyes, what you are actually looking at is atmosphere made solid, or more specifically,
carbon dioxide distilled and solidified out of the atmosphere thanks to the irresistible at-
tractions between carbon dioxide and the calcium princesses that dwell in the very heart
of the calcium-silicate rocks.
But these great deposits contain more than chalk. Even a casual look at the rocks of
the Seven Sisters will reveal a large number of hard nodules of flint that resist weather-
ing and are often transported over large distances by tides and currents. These flints are
made of the silica and oxygen weathered out of granite and basalt at the same time as
calcium. Washed into the rivers as silicic acid, the silica reaches the sea, where diatoms
(Figure 21)
, radiolarians and sponges precipitate it into exquisitely crafted glassy shells
and spicules that rain down to the murky depths of the ocean alongside the chalk shells
of the coccolithophores. How the minute glassy remains of these beings coalesce into
flint nodules is still somewhat of a mystery.
Figure 21: A diatom with its finely crafted silica exoskeleton. (
photo © Steve Gschmeissner /
Science Photo Library
)
Calcium bicarbonate from rock weathering is so plentiful in the oceans that marine
creatures face the very real danger of death by calcite encrustation, for calcium bicar-
bonate likes nothing better than to transmute itself into calcium carbonate by precip-
itating onto any available surface—just as it does in limestone caves. There is a deep
comfort for each atom of carbon, oxygen, hydrogen and calcium when they configure
themselves into calcite—a great sense of reassurance and stability for each of them in
