Relative dating rock layers Free online sex indan chat
This interactive asks you to use your knowledge of relative dating. Help us work out the relative ages of the layers of sedimentary rocks.
You need to work out the order in which rocks were formed, from youngest to oldest. Remember that younger sedimentary rocks lie on top of older ones and were horizontal when formed.
Fossils are important for working out the relative ages of sedimentary rocks.
Throughout the history of life, different organisms have appeared, flourished and become extinct.
The Principle of Original Horizontality states that due to the influence of gravity all sediment is originally deposited horizontally.
In other words, as sediment fills a depositional basins we would expect the upper most surface of the sediment to be parallel to the horizon. Using this principle we can than assume that sedimentary layers which have been deformed/folded must have been deformed after all affected layers have been deposited.
If conditions are right the remains of the dying organisms can then be preserved as fossils within the rock that formed from sediments that covered the remains.
Since, all sedimentary rock is formed through the gradual accumulation of sediment at the surface over time, and since the principle of superposition tells us that newer sediment is deposited on top of older sediment, the same must also be true for fossils contained within the sediment.
Some fossils, called index fossils, are particularly useful in correlating rocks.
The method of reading the order is called stratigraphy (layers of rock are called strata).
Relative dating does not provide actual numerical dates for the rocks.
For purposes of relative dating this principle is used to identify faults and erosional features within the rock record.
Then, by applying the Principle of Cross-Cutting we are able to relatively date those processes.