this post was submitted on 16 Aug 2026
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Explain Like I'm Five
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Radiocarbon dating works by knowing what portion of carbon-14 (an unstable radioactive isotope of carbon) remains present in an organic sample.
Plants and animals that eat plants take in carbon-14 and normal carbon in measurable proportions, and then when they die they stop taking in more new carbon 14, the ratio of carbon-14 to carbon then changes over time at a measureable rate we can use to determine the age of objects to about 60,000 years ago.
We didn't use carbon dating to determine the age of theia because all traces of carbon-14 would be long gone after 14 billion years.
I'm not familiar enough to speculate further, other methods of radiometric dating would likely have been used alongside other methods to determine the age of theia. Other radiometric methods use similar methods where we know the decay rate of certain radioactive materials, but for different date and age ranges than carbon.
Long dates are often uranium series dating using zircon crystals and a known baseline that can date things into the billions of years. When zircon is formed it excludes lead and includes uranium. The end of the decay chain of uranium is lead. The lead to uranium ratio will give you the age of the crystal. This means anything that includes that crystal is younger.
I don't think anyone would seriously say that Theia is 14 billion years old. The universe is about 14 billion years old. None of the planets of our solar system developed until about 4.6 billion years ago, and I wouldn't think the upper limit for the development of the hypothetical planet Theia (if indeed it ever did exist) could be much more than that 4.6 billion years ago figure. That said, your point certainly stands that Theia would be far older than that up "to about 60,000 years ago" figure, so carbon dating is inapplicable to any discussion around evidence for/against the Theia hypothesis.
I just wrote the wrong number. Thing said 4.5b
Citation needed
(Emphasas mine.)