Two types of fossil dating
What’s more, if the whole rock is badly weathered, it will be hard to find an intact mineral grain containing radioactive isotopes.You might have noticed that many of the oldest age dates come from a mineral called zircon.On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.26 billion years.
If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric (absolute) age dating as well.That’s because zircon is super tough – it resists weathering. Each radioactive isotope works best for particular applications.The half-life of carbon 14, for example, is 5,730 years.The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample.By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: t = [ ln (0.10) / (-0.693) ] x 5,700 years t = [ (-2.303) / (-0.693) ] x 5,700 years t = [ 3.323 ] x 5,700 years Because the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old.
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Pretty obvious that the dike came after the rocks it cuts through, right?