Stratigraphic dating assumes that the lower layers in any particular profile are older than the upper layers in that profile ("the law of superposition") and that an object cannot be older than the materials of which it is composed.Igneous masses are dated according to whether they caused metamorphism in the surrounding rock (proof of emplacement in preexisting rock) or whether sediments were deposited on them after they were formed.The media on this page may not be supported on your device.
In geology, a master stratigraphic sequence for a particular region is built up by correlating the strata from different locations with one another.
As new locations are investigated, the geologist attempts to fit the new profiles into the master sequence of geological strata for that region.
The Sciencelearn Hub is in the process of converting most of the media to formats supported by touch devices, so please try accessing this resouce on your touch device at a later date. Help us work out the relative ages of the layers of sedimentary rocks.
Remember that younger sedimentary rocks lie on top of older ones and were horizontal when formed.
Fossils are useful because certain assemblages of species are characteristic of specific geological eras.
Pollen analysis, or palynology, involves the microscopic examination of fossil pollen grains in stratified peat and lake deposits.
Through the investigation of many different stratigraphic contexts, a master sequence of fossil and floral assemblages may be devised for a region.
Fossils is an identification event which rotates with Rocks and Minerals every three years.
According to this system, humans passed through three distinct stages of technological development, based on the primary material used to manufacture tools and weapons: the Stone Age, the Bronze Age, and the Iron Age.