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Fossils
Relative Dating

The science of determining the relative order of past events, without necessarily determining their
absolute age

Absolute dating

The process of determining an age on a specified time scale in geology. Some scientists prefer the
terms chronometric or calendar dating.

The principle of superposition

This states that…

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Body Fossils

Organisms consist of soft tissues, and hard skeletal materials which may be inorganic

When organisms die scavengers may eat them. If they escape this terrible fate, bacteria and fungi
will feed on the organic remains: this is the process of decay. The inorganic materials are
eventually dissolved by…

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Trace Fossils

Trace fossils are sedimentary structures produced by the activity of organisms, as distinct from the
body fossils which are preserved remains. They include:

Tracks Trails Burrows Borings






Resting place











FOSSIL ASSEMBLAGES

Many organisms are moved by natural processes (such as water currents) after death BEFORE
PRESERVATION. If so,…

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TRILOBITES (WOOOOOOOOO)

Exclusively marine, they had an external jointed protein skeleton; the body consisted of three
sections: the cephalon (head), thorax and pygidium (tail). Most were benthic (sea bed) crawlers;
some were shallow burrowers, and others swam. If a species has eyes, there must have been light
to see by,…

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A zone fossil used to: determine the relative age/date of rocks or to correlate rocks of the same
age.
Brachiopods

An exclusively marine species, they lived on the sea floor, filtering food from sea water. The shell,
consisting of two valves: a large pedicle valve, and a smaller brachial valve.…

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Increased surface area hence increased food intake

Bivalves

Includes freshwater and marine species. All are filter feeders. Some live on the sea floor, others
burrow into sediment, 'glue' themselves to rocks or bore their way into driftwood. Some are
capable of short bursts of swimming (just keep swimming right). Shell,…

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Ammonites

Ammonites are an extinct group of marine invertebrate animals. Robust, onepiece, flat spiral
calcium carbonate shell. The shell was divided into gasfilled chambers by partitions called septa.
Where each septum met the external shell, it produced a suture line. Each species had a unique
suture line. Some species had…

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The coil and chambers (septa) were used as buoyancy to allow the Ammonoid to float. Many
Ammonoids probably lived in the open water of ancient seas, rather than at the sea bottom. Ate
plankton.



Ammonoids are a good zone fossil because

Wide and Plentiful distribution
Ready preservation
Rapid Evolutionary Change…

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Marine conditions
Warm water (best between 25 29°C)
Clear water to allow sunlight through
Shallow water (photic zone)
High energy (breaking waves) aerated
Welloxygenated water

Hard outer skeleton CORALLITE.

SEPTA ­ radial plates grown from corallite wall into the

Coral centre to support the "bag of guts" coral on the…

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