Radiometric dating of sediments

Posted by / 02-Jul-2020 23:53

Radiometric dating of sediments

It is therefore important to try to ensure that decay has taken place in a 'closed system', with no loss or addition of isotopes, by using only unweathered and unaltered material in analyses.The radiometric decay series commonly used in radiometric dating of rocks are detailed in the following sections.This is the most widely used system for radiometric dating of sedimentary strata, because it can be used to date the potassium-rich authigenic mineral glauconite and volcanic rocks (lavas and tuffs) that contain potassium in minerals such as some feldspars and micas.One of the isotopes of potassium, 40 K, decays partly by electron capture (a proton becomes a neutron) to an isotope of the gaseous element argon, 40 Ar, the other product being an isotope of calcium, 40 Ca.The choice of method of determination of the age of the rock is governed by its age and the abundance of the appropriate elements in minerals.The samples of rock collected for radiometric dating are generally quite large (several kilograms) to eliminate inhomogeneities in the rock.

It is also possible to use it on authigenic minerals, such as glauconite, in some sedimentary rocks.Up to this time estimates of the age of the Earth had been based on assumptions about rates of evolution, rates of deposition, the thermal behaviour of the Earth and the Sun or interpretation of religious scriptures.Radiometric dating uses the decay of isotopes of elements present in minerals as a measure of the age of the rock: to do this, the rate of decay must be known, the proportion of different isotopes present when the mineral formed has to be assumed, and the proportions of different isotopes present today must be measured.The samples are crushed to sand and granule size, thoroughly mixed to homogenise the material and a smaller subsample selected.In cases where particular minerals are to be dated, these are separated from the other minerals by using heavy liquids (liquids with densities similar to that of the minerals) in which some minerals will float and others sink, or magnetic separation using the different magnetic properties of minerals.

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This results in an underestimate of the age of the rock.

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