Radioactive dating geology
by Tas Walker A geologist works out the relative age of a rock by carefully studying where the rock is found in the field.
The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them.
Radiocarbon dating works because an isotope of carbon, C, is constantly formed in the atmosphere by interaction of carbon isotopes with solar radiation and free neutrons.
Living organisms absorb carbon (for example, we breathe it in).
From the mapped field relationships, it is a simple matter to work out a geological cross-section and the relative timing of the geologic events.
His geological cross-section may look something like Figure 2.
Scientific knowledge of Earth’s geologic history has advanced significantly since the development of radiometric dating, a method of age determination based on the principle that radioactive atoms in geologic materials decay at constant, known rates to daughter atoms.
...calculation was based on the assumption that the substance of the Earth is inert and thus incapable of producing new heat.
...igneous activity (both extrusive and intrusive) occurred in the Caledonian mountain belt, which stretched from New England, Nova Scotia, Newfoundland, Scotland, and Scandinavia to eastern Greenland.
Radiometric dating of granitic intrusions associated with the Caledonian orogeny yields ages between about 430 million and 380 million years.
His estimate came into question after the discovery of naturally occurring radioactivity by the French physicist Henri Becquerel in 1896 and the subsequent recognition by his colleagues, Marie and Pierre Curie, that compounds of radium (which occur in uranium minerals)...
Another role of isotopic geochemistry that is of great importance in geology is radiometric age dating. Beginning with studies in the 1950s, a much better chronology and record of Pleistocene climatic events have evolved through analyses of deep-sea sediments, particularly from the oxygen isotope record of the shells of microorganisms that lived in the oceans.