Can the age of rocks be measured accurately?
- Radiometric rock dating techniques, attempt to measure the age of rocks.
- There are several different methods of analysis: Uranium-Lead (U/Pb), Potassium-Argon (K/Ar) etc.
- They measure the amount of uranium (U) and lead (Pb) in a small sample of the rock.
- The 'half-life' rate of decay of uranium into lead, is well known.
- An assumption is then made, about how much uranium (& lead) was in the rock, when it originally formed.
- The difference (original - now) is used to calculate the age of the rock, using the 'half-life' rate of decay.
- Do you see the flaw?
- The original assumption gives the final answer.
- They have no idea how much uranium (or lead) was in the rock when it formed, so they've no idea how old the rock is.
Q1: Why do rock dating techniques give widely different answers?
- They analyse a rock sample, and if it gives the 'wrong' age, they just discard that result.
- They repeat the analysis with another sample from the same rock.
- They keep doing this, until they get an answer they're happy with!
- Rocks from volcanic events within the last 200 years, can return "dates" anywhere from 1 million to 100 million years or more!
- A standard question they generally ask, when you take a rock to be measured is: "What age are you expecting?"
- I.e. They'll test the rock until they obtain an answer that fits your "assumption," because they are just guessing.
- They use rocks to date fossils, and fossils to date rocks - circular logic.
Solution: Nobody knows how old rocks are.