Relative age dating of rocks definition
Tephrochronology is the study of volcanic ash deposits.Volcanic ash layers often have unique chemical and physical characteristics that can be used for correlation.Oxygen isotopes (-O) are widely used in correlation of Quaternary marine sediments.Oxygen isotope concentrations in mollusk shell and calcareous algal material normalize with seawater while the organisms are alive.Paleomagnetism can be used in conjunction with other correlation or dating methods to establish the age or rocks or to decipher changes in a rock's orientation through time.In Menlo Park, contact: Dwayne Champion for more information about the paleomagnetic lab.
Micropaleontologists and palynologists work with microscopes or scanning electron microscopes (SEM).
The basic science behind this method is that calcareous shell material incorporates the two strontium isotopes in the same ratio that occurs in seawater at the time the organism was alive.
At different times in Earth's history, the relative abundance of these two isotopes in seawater gradually changed through time (such as during the Permian, the Late Cretaceous, and parts of the Tertiary).
The Sr geochronology method involves extracting these isotopes from fossil shell material (only several milligrams of sample are necessary for X-ray fluorescence spectroscopy).
The ratio of these two isotopes derived from a sample is compared with a database of known samples to determine relative ages.
Relatively young deposits can be sometimes dated using tree rings, varved-lake sediments, coral growth patterns, and other methods.