Dating Methods Using Radioactive Isotopes
Isotope Systems Used for Radiometric Dating. Isotope system Adapted from Table , Press, F. and Siever, R.,, Understanding the Earth, 2nd ed. Radioactive hourglasses are used to date the relics of bygone civilizations, Carbon is a radioactive carbon isotope present in the atmosphere, plants and Nature has done us in providing a table of elements bursting with radioactive. Using relative and radiometric dating methods, geologists are able to answer the question: how old is Figure 5: Radioactive isotopes and how they decay through time. Some commonly used dating methods are summarized in Table 1.
Radioactive elements tend to become concentrated in the residual melt that forms during the crystallization of igneous rocks.
Radioactive isotopes don't tell much about the age of sedimentary rocks or fossils. The radioactive minerals in sedimentary rocks are derived from the weathering of igneous rocks.
If the sedimentary rock were dated, the age date would be the time of cooling of the magma that formed the igneous rock.
The date would not tell anything about when the sedimentary rock formed. To date a sedimentary rock, it is necessary to isolate a few unusual minerals if present which formed on the seafloor as the rock was cemented. Glauconite is a good example.
Radiometric dating - Wikipedia
Glauconite contains potassium, so it can be dated using the potassium-argon technique. The fear was that if its age could be traced to the beginning of the first millennium, then it might well be named a Church Relic -- but one that had to be mutilated to gain that stature. Meanwhile, back at the lab, techniques continued to improve, until reliable radiocarbon dating could finally be done with considerably smaller samples in the case of the Shroud, just a few short strands were needed for each sample.
Such small sample sizes were judged by Church authorities not to constitute mutilation and the analysis went forward. Samples were taken from the Shroud and sent to several laboratories along with other samples of fabrics of known ages. The laboratories were not told which was which.
The reported values showed close agreement between the Shroud samples and none suggested an age of the fabric having been harvested from plants before the 12th century A. The committee which had taken on the task of judging the validity of the analysis was sufficiently satisfied to convince local Church authorities to retire the claim that it is a Holy Shroud.
Potassium-argon method There is another often used dating technique for samples considerably older than 60, years. It is called potassium-argon dating and is based upon the detected ratio of 40Ar to 40K in a given sample.
Natural potassium is composed of 0. The latter route has a half-life of 1.
The model says that as molten rock solidifies slowly, dissolved gases are displaced from the crystalline solid which forms because the gas molecules are excluded from the crystalline lattice positions.
If crystals with uniform lattices form they may be candidates for potassium-argon dating. Many minerals contain the element potassium. In the radioactivity hourglass upper part, that gradually empties, are decaying nuclei.
At the bottom part, slowly filling up, are the nuclei resulting from these decays. CEA Radioactive hourglasses are used to date the relics of bygone civilizations, by measuring the amount of Carbon, whose decay rate allows for precise age calculations.
Carbon is a radioactive carbon isotope present in the atmosphere, plants and living bodies. Radioactive dating can also be applied to the dating of rocks as old as the Earth, of coral and volcanic lava.Half-Life and Radioactive Decay
Anything between a few hundred years to several billion years old can be dated. Archaeologists, geologists, physicists can choose between array of radioisotopes Let us quote the words of one scientist: