Geology Reference
In-Depth Information
Geological time.
To give an idea of the enormity of Precambrian time, the table
opposite can be displayed as a clock where the Precambrian is seen
to occupy almost ninety per cent of geological time. Man appears a
few seconds before midnight.
biological diversity. It was succeeded by the 'Cretaceous' which
takes its name from the Latin word for chalk - creta - its most
conspicuous and widespread deposit, exemplified in the White
Cli¬s of Dover. Chalk is composed chiefly of coccoliths, the
microscopic shelly remains of single-celled algae, and hence is
primarily of plant origin. It is impossible to imagine how many
must have died to make up one stick of chalk, let alone a whole
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