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With this in mind geologist have long known that the deeper a sedimentary rock layer is the older it is, but how old?
Although there might be some mineral differences due to the difference in source rock, most sedimentary rock deposited year after year look very similar to one another.
The most obvious feature of sedimentary rock is its layering.
This feature is produced by changes in deposition over time.
With out individual time stamps the process of dating these structures could become extremely difficult.
To deal with many of these problems geologists utilize two types of geologic time: relative time and absolute time.
Relative dating uses the principles or laws of stratigraphy to order sequences of rock strata.
Steno also noticed that fossil seashells could be found in rocks and mountains far from any ocean. Steno proposed that if a rock contained the fossils of marine animals, the rock formed from sediments that were deposited on the seafloor. Relative age means age in comparison with other rocks, either younger or older.
Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.
This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the .
organisms, geologists employ a variety of techniques.
These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events.