Dating fossils and rock
This is because new sediments are always laid down on top of sediments that have already been deposited.
So, when looking at the history of a cliff face, it is important to read the story it tells from the bottom layer up.
New discoveries have filled in the gaps, and shown us in unimaginable detail the shape of the great ‘tree of life’.
Darwin and his contemporaries could never have imagined the improvements in resolution of stratigraphy that have come since 1859, nor guessed what fossils were to be found in the southern continents, nor predicted the huge increase in the number of amateur and professional paleontologists worldwide.
Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.In an undisturbed sequence of rocks, such as in a cliff face, it is easy to get a rough idea of the ages of the individual strata – the oldest lies at the bottom and the youngest lies at the top.The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly.Scientists use two kinds of dating techniques to work out the age of rocks and fossils. This considers the positions of the different rocks in sequence (in relation to each other) and the different types of fossil that are found in them.