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| Geological photographs from around the world | ||||||||
In the early 1800s, William Smith, a civil engineer and the 'father of modern geology' observed that the fossils found in one layer of sedimentary rock are different from those in the layers above and below. One assemblage of fossils is characteristic of one age. We now know that these differences are due to evolution.
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If strata in different parts of a region (or even in different parts of the world) contain the same fossils,
they must have been deposited at the same time and therefore belong to the same geological time zone.
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Some types of fossils are more useful than others for correlation. Ammonoids (see photograph) and graptoloids
are good zone fossils (zonal indices).
This relative dating puts events into order. It does not say how long ago it happened. Absolute dating, in years,
is carried out using the radioactive isotope carbon-14, although this will only give an age for organic material
which is younger than 50,000 years - not very long in the geological time scale.
- explains the principles of correlation;
- describes the main features of zone fossils;
- gives examples of good zone fossils;
- explains the radio-carbon method of dating;
- outlines the limitations of radio-carbon dating.
'Zonr Fossils' is part of the Geopix Fossils Study Guide CD.
To order this CD go to the Geopix Online Store
The Study Topic contains the following pages:
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