Area of study 2. How old is that fossil?. Fossils tell us what kinds of organisms lived in the past, but how do scientists determine the age of a fossil? There are a number of ways to do this:
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Upper strata must have formed later and be younger. This is the relative dating method of stratigraphy.
The rate of decay of the element is independent of the nature of the rocks or the environmental conditions to which they are exposed, so they act as accurate clocks.
The method of radiocarbon dating is limited to samples not older than 50 000 years, because by that age there is very little 14C left.
However, times were about to change and the Permian marked the close of the Palaeozoic.
At the end of the Permian period, animal groups such as trilobites and some groups of ammonoids died out forever.
For this reason all of these organisms are called tetrapods (literally meaning ‘four-footed’).
Thus, when biologists attempt to work out evolutionary relationships, they must distinguish between homologous and analogous features.
The early embryo has a similar structure or basic plan in all members of a particular group of the animal kingdom.
It is interesting that von Baer’s law was formulated before evolution was widely accepted.
For example, whales have vestigial pelvic bones, bones found well developed in other groups of mammals
SAC 3Outcome 2: Analyse and evaluate evidence for evolutionary change and evolutionary relationships, and describe mechanisms for change including the effect of human intervention on evolutionary processes.
Written response 2: A response to an issue related to an application of gene technologies – Cystic Fibrosis scenario