Aka radiocarbon dating aka carbon-14 dating is a method is a method for determining the age of old stuff, up to about 50- or 60,000 years old. I was under the impression it was useful for determining the age of far older things, so I will have to investigate further.
This method was developed in the late 1940s, and it is fascinating: radiocarbon is constantly created in the Earth’s atmosphere by cosmic rays interacting with nitrogen in the atmosphere. This produces radioactive carbon dioxide, which goes into plants via photosynthesis. The plant is then eaten by an animal (including humans). When the plant or animal dies, it no longer exchanges carbon with its environment, and the carbon begins to undergo radioactive decay. Measuring the amount of carbon present can help us determine when a plant or animal died. The half-life of carbon is roughly 5730 years, so this process can help determine the age of items 40-50k years, like I mentioned.
The Wikipedia page then says, “although special preparation methods occasionally make an accurate analysis of older samples possible.” Uhhhhh… that simply generates more questions. Firstly, I have seen — recently — estimates of millions and billions of years that I foolishly assumed were quantified by some straightforward technique. Now, I have more questions.