Dear All:
Has nobody heard of the White Cliffs of Dover? They are made of chalk.
Most chalks – including the famous White Cliffs - formed during the Cretaceous period, between 100 and 60 million years ago. Chalks from this period can be found around the world, and they consist of the microscopic skeletons of oceanic plankton.
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The Coccolithophores are the major group of chalk forming plankton. Their individual spherical skeletons are called cocospheres and they consist of a number of calcareous discs called coccoliths. After death of the plankton, the skeletons settled to the bottom of the sea and most coccospheres and coccoliths collapsed, but they can be clearly seen using scanning electron microscopy (SEM). Indeed, back in my days working in a lab. I often used chalk as a demonstration of SEM to visiting parties of non-scientists because coccospheres are pretty.
Cretaceous chalks formed when global temperatures and atmospheric carbon dioxide concentration were higher than now. Indeed, global temperature was 5 to 6 deg.C higher than now and atmospheric carbon dioxide was 4 times higher than now
(see e.g.
http://www.jstor.org/pss/57127).
But the calcerous skeletons of oceanic creatures from that time are so abundant that they now comprise many hills and mountains around the world.
So, I wonder why some people fear that slightly higher global temperatures and slightly higher atmospheric carbon dioxide concentration than now would hinder formation of such skeletons.
All the best
Richard
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