To explain.
Let’s say they have a method that can test bone age. Up to let’s say 1-2k years we can know for sure it’s accurate, since we might have believable records on the bones proving that the age test is accurate.
Past a certain age though there’s no more records. How can we know the testing is accurate and not just the method only going up to that limit and being inaccurate on anything older? Or are we just assuming?
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They use multiple independent methods to corroborate.
First is relative dating. There idea that objects buried deeper, are older. It’s also documented at any site you find the object or one similar to it. This allows you to compare, and try to account for any missing layers or irregularities.
For example you find layers of rock types, other recognizable objects, fossils etc. Say in the order below
134a89
At another site the layers are
23a698
“A” our mystery object appears it same sequence in both sites. There is some variation, as some markers didn’t survive in both sites (never got deposited, eroded, extinct in the area at that time etc)
And every site we check we compare and see how consistent it is, how it is placed based on others etc.
This doesn’t tell us exactly how old it is. But we can pretty confidently say from the two samples down that it’s older than 123 and younger than 689.
But this is only one method.
Another is looking for any market that has a fairly consistent change over time. A big one is the way ice looks when deposited in the summer or the winter. It’s more clear when deposited in dinner months and more cloudy with trapped gas in the winter. This allows researchers to essentially count cycles or years to get a good estimate of the age. There is some uncertainty of course, as layers can get destroyed.
But again, it’s checked against multiple sites, and researchers examine samples for abnormal signs and document possible lost years. Say signs of a summer layer that bleeds into a winter layer may indicate an event that melted a lot of ice.
These are compared to relative dating, if we find an object embedded in such a sample.
Then there is the radioactive dating as described by other posters. Again once this value is find, it’s checked against the others to see if it lines up.
So you find an object, let’s say a bronze knife, and plane it in the local record based on relative dating. It’s found “above” obsidian and flint tools, and under an interesting layer of ash.
Across the country someone else finds a bronze pot. No obsidian tools, but they did find the ash layer and their bronze pot is under that.
We’re getting an indication that bronze work occurred before that eruption, and not that this knife was buried or accidentally put lower.
Radioactive dating out the two objects within a couple bonded years of each other, another supporting piece.
And then geologists start placing the ash layer the same way we placed the bronze knife, fitting it into the geologic record using both relative and radioactive dating. This places it younger than bronze knife at every location.
Sunshine finds an ash layer in artic ice cores… And use the later method to date it. They find it’s date and composition of trace minerals matches the one in our region. And the later method backs up the radioactive and relative dating.
One single method of dating isn’t ironclad, but having several all give similar results puts it beyond reasonable doubt. Having all of those be wrong, across multiple sites is incredibly unlikely.
And we also find that the radioactive dating method is incredibly reliable, so much so that it becomes the primary line of dating evidence. Good enough that even if it’s all we get, it’s viewed as correct because it works fine and again when checked against other methods.
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