The potassium-argon age of some meteorites is as old as 4,500,000,000 years, and volcanic rocks as young as 20,000 years old have been measured by this method.
The potassium-argon (K-Ar) isotopic dating method is especially useful for determining the age of lavas.
Following death, however, no new carbon is consumed.
Progressively through time, the carbon-14 atoms decay and once again become nitrogen-14.
decay or the rate of other cumulative changes in atoms resulting from radioactivity. The various isotopes of the same element differ in terms of atomic mass but have the same atomic number..
One half-life is the amount of time required for of the original atoms in a sample to decay.
Any alteration or fracturing means that the potassium or the argon or both have been disturbed.
The site also must be geologically meaningful, clearly related to fossil-bearing rocks or other features that need a good date to join the big story.
This allows the dating of much older and smaller samples but at a far higher cost.
is known to cause grave problems in regional geochronology studies.
For example, in the Middle Proterozoic Musgrave Block (northern South Australia), a wide scatter of K-Ar mineral "ages" was found, ranging from 343Ma to 4493Ma due to inherited (excess) , permitting inclusion of the gas in the crystallizing minerals.
Although, organic materials as old as 100,000 years potentially can be dated with AMS, dates older than 60,000 years are still rare.
Paleoanthropologists and archaeologists must always be aware of possible radiocarbon sample contamination that could result in inaccurate dates.