Relative date is provided to arrange geology events, and also the rocks they leave behind, in a sequence. The method of reading the stimulate is called stratigraphy (layers of rock are dubbed strata). Family member dating walk not administer actual numerical dates for the rocks.

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Next time you find a cliff or road cutting with many rock strata, try working out the age order using some simple principles:

Sedimentary rocks are usually laid under in order, one on optimal of another. In a sequence, the oldest is in ~ the bottom, the youngest is in ~ the top. This is the rule of ‘superposition’.
most sedimentary rocks space laid under in flat (horizontal) layers, back these have the right to later tilt and fold. This is the rule of ‘horizontality’. Great of sedimentary rock expand sideways in the exact same order. A later event, such together a river cutting, may type a gap, yet you can still attach the strata. This is the rule of ‘lateral continuity’.

Fossils and relative dating

Fossils are crucial for working out the relative eras of sedimentary rocks. Throughout the background of life, different aramuseum.organisms have actually appeared, flourished and also become extinct. Numerous of this aramuseum.organisms have left their stays as fossils in sedimentary rocks. Geologists have studied the order in which fossils appeared and disappeared with time and also rocks. This examine is referred to as biostratigraphy.

Fossils can aid to enhance rocks that the exact same age, even when you find those rocks a long way apart. This matching procedure is referred to as correlation, which has been vital process in constructing geological timescales.


Some fossils, called index fossils, are an especially useful in correlating rocks. For a fossil to it is in a good index fossil, it demands to have lived during one certain time period, be straightforward to identify and also have been abundant and also found in countless places. For example, ammonites resided in the Mesozoic era. If you uncover ammonites in a rock in the south Island and additionally in a rock in the north Island, you can say that both rocks are Mesozoic. Different types of ammonites lived at various times in ~ the Mesozoic, so identifying a fossil species can aid narrow down when a rock was formed.


Correlation have the right to involve matching an undated rock through a date one at an additional location. Expect you uncover a fossil at one ar that can not be dated making use of absolute methods. That fossil species may have actually been date somewhere else, so girlfriend can match them and say the your fossil has a comparable age. Several of the most valuable fossils because that dating purposes are very small ones. For example, microscopic dinoflagellates have been studied and also dated in great detail approximately the world. Correlation through them has actually helped geologists, such as Professor James Crampton, day many brand-new Zealand rocks, including those containing dinosaurs.


Bring family member dating ethics to life v the task Rock layers and relative dating. Students start by observing a photograph and also a diagram of rock layers close to Whanganui, watch an animation about how the layers to be formed, then usage an interactive labelling diagram to work out the bespeak in i beg your pardon the rocks were created. The activity offers literacy opportunities and also practice using the science capacity "Interpret representations".

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