In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young (radiocarbon dating with Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes.
When they find one, they gather a sample of the hardened lava and send it off to a laboratory to test it for radioactive elements.
When a volcano erupts, hot, molten rock (called “lava”) from deep inside the Earth is released. Elements are the “building-blocks” of the universe (for example, water is made from the elements hydrogen and oxygen).
C in the atmosphere haven’t been constant throughout history (for instance, Noah’s Flood lowered the total amount of available carbon by burying lots of animals and plants).
So something that lived (and died) when the proportion of C was less than normal would appear to have died more years ago than it actually did (for example, it might give an age of 3,000 years before the present, rather than its true age of 2,000 years).
Of course, the best method is to check the account of a reliable eyewitness, if one is available. Since it is the written Word of God, we can trust it to tell us the truth about the past.
Carefully studying the Biblical record, we find that the universe has an age of around 6,000 years, and that a world-changing, global Flood occurred about 4,300 years ago.
But even radiometric dating does not actually directly measure the age of something (there is no substance called “age”).
It measures the amounts of certain radioactive substances.
Most people think that scientists can actually measure the ages of rocks, using a method called “radiometric” or “radioisotope” dating.