Radiometric dating easy definition
Most rocks contain uranium, allowing uranium-lead and similar methods to date them.
Other elements used for dating, such as rubidium, occur in some minerals but not others, restricting usefulness.
Note that although carbon-14 dating receives a lot of attention, since it can give information about the relatively recent past, it is rarely used in geology (and almost never used to date fossils).
Carbon-14 decays almost completely within 100,000 years of the organism dying, and many fossils and rock strata are hundreds of times older than that.
The oldest rock so far dated is a zircon crystal that formed 4.4-billion-years ago, which was only 200 million years or so after the Earth itself formed.
Given isotopes are useful for dating over a range from a fraction of their half life to about four or five times their half life.It suffers from the problem that rubidium and strontium are very mobile and may easily enter rocks at a much later date to that of formation.This method for rock dating is based on the decay of potassium-40 into argon: until the rock solidifies, argon can escape, so it can in theory date the formation of rock.Due to the long half-life of uranium it is not suitable for short time periods, such as most archaeological purposes, but it can date the oldest rocks on earth.A proper radiometric date should read years before present (with 1950 being present) ± range/2 at x standard deviations (Xσ)', but is often reported as a single year or a year range, like 1260–1390 CE (the date for the Shroud of Turin).