Date/Time 13 Jul 2014 12:09:20am
Alan Marshall,
Further my 2) above, perhaps you should not be swayed too much by sources famous for favouring alarmism. For a start, I think you need to study the geology of the chalk cliffs of England and France. Here is an extract from one source:

QUOTE: Chalk often forms spectacular clifflines, the most famous of which are the 'White Cliffs of Dover.' It is comprised of a sequence of mainly soft, white, very fine-grained extremely pure limestones which are commonly 300-400 m thick. These rocks consist mainly of coccolith biomicrites formed from the skeletal elements of minute planktonic green algae, associated with varing proportions of larger microscopic fragments of bivalves, foraminifera and ostracods. The planktonic coccoliths and many of the foraminifera (the planktonic species) lived floating in the upper levels of the oceans. When they died their skeletons sank to the bottom, combining with the remains of bottom living bivalves, foraminifera and ostracods, to form the main components of the Chalk. UNQUOTE

Almost by definition, the purest form of limstones, chalk, were formed in warm clear seas, after deposition. (like in the Caribbean today?). In the case of England/France, this was around 65-100 million years ago, when atmospheric CO2 was much higher than today, and the seas warmer. See for example:

There are of course less pure limestones formed when CO2 levels were even higher, but in probably cooler more turbid water, and containing larger shelled fossils such as ammonites, e.g. Purbeck Stone (south central English coast)

Still, we don’t want to hear any good news, do we?
