The calculated age is the age from which the rock or mineral stabilized.
The interpretation of the age date also depends somewhat on the kind of rock being analyzed.
Geologists have calculated the beginning and ending dates for the eons, eras, periods, and epochs of the geologic time scale, and major geologic events.
To date, the oldest rocks discovered on the earth are from northwestern Canada and are 3.964 billion years old.
For example, the half‐life of U‐238 is 4.5 billion years.
Thus, if you began with one gram of U‐238, 4.5 billion years later only one‐half gram would remain.
QUESTION: Can we date sedimentary rocks using radiometric dating techniques?
ANSWER: Sedimentary rocks cannot be dated directly using radiometric dating, which is based on the idea that when rocks are in liquid form, their radiometric clock resets.This radioactive decay begins after the elements are locked into crystalline mineral structures.Some elements have variations called isotopes, which are atoms that contain different numbers of neutrons in their nuclei.The important boundary between the Paleozoic era and the Precambrian era is dated at about 570 million years ago; the Mesozoic era (the “Age of the Dinosaurs”) started about 245 million years ago and ended 66 million years ago.Radioactive elements decay at known rates of speed.Absolute age dates have confirmed the basic principles of relative time—for example, a uranium‐lead date from a dike that intrudes into an older rock always yields an absolute age date that is younger than the absolute age date of the enclosing rock.