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A number of radioactive isotopes are used for this purpose, and depending on the rate of decay, are used for dating different geological periods.

More slowly decaying isotopes are useful for longer periods of time, but less accurate in absolute years.

The sediment samples must remain totally undisturbed during sampling to obtain the best possible dating.Subsequently, they are cut into slices of approximately 1 cm and dried, whereupon the content of dry matter and possibly the loss on ignition are determined.Biostratigraphy does not directly provide an absolute age determination of a rock, but merely places it within an interval of time at which that fossil assemblage is known to have coexisted.Both disciplines work together hand in hand however, to the point where they share the same system of naming rock layers and the time spans utilized to classify layers within a stratum.Marker horizons are stratigraphic units of the same age and of such distinctive composition and appearance, that despite their presence in different geographic sites, there is certainty about their age-equivalence.

Fossil faunal and floral assemblages, both marine and terrestrial, make for distinctive marker horizons.Two methods of paleomagnetic dating have been suggested (1) Angular method and (2) Rotation method.Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and/or volcanic rocks by comparison to the magnetic polarity timescale.The science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material.Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure.