The table below summarises key features: Gastrioceras listeri is a particularly good example of a ZONE fossil.As it is free swimming it could have travelled a considerable distance.When found in rocks as far away as Australia you could reasonably expect those rocks to be the same age as those in Cliviger Valley!

principles of relative dating of geologic events-80

If the geological record was 100% complete and there were no breaks in sedimentation, the stratigrapher's job would be an easy one.

However, breaks in sedimentation do occur and when this happens, geologists' refer to this missing strata as an unconformity.

Techniques of accurately dating rocks is crucial in establishing the time-gap that exists.

The laws of physics and chemistry that governed geologic processes in the past are the same as those that govern processes now and in the future.

The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.

These ages have been derived from relative dating and absolute dating (radiometric dating) of rock layers and fossils.

(a) Relative Dating This technique uses principles of stratigraphy (rock strata) and the study of fossils (palaeontology) to determine the relative ages of rocks and sediments. Field geologists' rely on a number of simple techniques for dating rocks and constructing geological successions. The Law of Strata Identified by Fossils is a little bit more complex.

(relative geologic timescale) (b) Absolute Dating Following the discovery of radioactivity in 1895, radiometric dating techniques were developed to determine the absolute ages, i.e. In the succession of strata, each layer represents the geographical conditions that occurred over that area at the time the layer was deposited.

In each period of earth's history different fauna and flora evolved with similar faunas being characteristic of similar beds.

The diagram right shows two distinct faunal assemblages.

What can be deduced from our two distinct faunas in terms of their usefulness in the relative dating of rocks?