Talk:Age of the Earth

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Article should clearly explain where the current figure comes from[edit]

For such a long, meandering, well-cited article, it's disappointing that it never actually says how we know the Earth is 4.5 billion years old. There are clues - we can see that the main evidence has to do with the radioactive decay of uranium into (ultimately) lead and the Canyon Diablo meteorite, but there should be a couple of paragraphs that fill in the missing details and connect the dots. I certainly don't know how radiometric dating gets us a number, but it seems like you'd have to know how much uranium was in the Canyon Diablo meteorite at the time Earth was formed, and I don't see anything that explains that.

Calculations aren't necessary - just the concepts. And it should be in a section at the top of the article and not interspersed with history. It doesn't matter for this purpose who figured it out and when.

So if someone understands how the age of the Earth is known, please write such a section.

This is the topic of the science of geochronology. Geochronology has its own wikipedia article already.

One other thing: it's probably not obvious to every reader what the definition of the age of the Earth is, so a paragraph explaining how the Earth was formed and what constitutes its birth would also be helpful. Likewise, the article speaks in places about the age of rocks and it isn't clear what counts as the birth date of a rock. I tend to think I've created a rock when I chip a piece off of a boulder, but I know that's not the kind of age we can get from radiometric dating. — Preceding unsigned comment added by Giraffedata (talkcontribs) 06:57, 30 April 2014

The first two paragraphs of the lede do a good job of summing up that information, and the bulk of the article covers radiometric dating and how several different techniques and methodologies all converge to the same date. What more do you want? TechBear | Talk | Contributions 13:13, 30 April 2014 (UTC)
We have a separate article on Uranium-lead dating, which is linked from the lede, and explains the method(s) in quite a bit of detail. There are different methods, but in general, no, you don't need to know the amount of uranium in the original sample, either because one uses a mineral that by its crystalline structure has none of the daughter element (in this case, lead) when it forms, or because one uses isochron dating, where the different ratios in different minerals are used to establish the original distribution. But I think these details are indeed better off in the specialized sub-articles. Stephan Schulz (talk) 15:34, 30 April 2014 (UTC)
The birth date of a rock was when it last froze from a molten state (lava). Potassium-Argon dating is the easiest to understand in this context:

Contradictory figures in first sentence[edit]

Maybe I'm missing something here, but surely 4.54 ± 0.07 billion years is 4.54 × 109 years ± 2%, not 4.54 × 109 years ± 1%. Doesn't 1% of 4.54 × 109 = 0.0454 billion? Benboy00 (talk) 22:56, 19 July 2014 (UTC)

Looking at the sources I had access to, as well of the rest of the article, it seems to me that the 1% figure is much more prevalent. Therefore, I changed the lede to read 4.54 ± 0.05 billion years (rounding up from 0.0454 to make the sig figs match). Benboy00 (talk) 23:06, 19 July 2014 (UTC)