It seems really farfetched to me, are we counting fossil rings or something?
In: Chemistry
It’s possible to date some substances very accurately. One example is using Potassium-Argon to date volcanic rocks.
When molten rock solidifies, it will usually form a crystal structure. Ordinary, argon will not form part of this structure; it’s a noble gas and thus doesn’t interact with other elements strongly enough.
However potassium will participate in forming that crystal… and one of it’s isotopes (Potassium-40) is unstable and decays to Argon-40. When that happens, the argon is trapped in the crystal. The ratio of Potassium-40 to Argon-40 in the rock allows you to figure out how long it was since the molten rock cooled. When the rock is newly formed, there’s almost no Argon-40 in it. After about a billion years, there will be a 10:1 ratio Potassium-40:Argon-40.
Once you’ve found the absolute age of something, you can then date things relative to that. Find the fossil of some poor dinosaur that got caught in a lava flow, and date the lava flow? Well obviously that dinosaur was alive at about the same time as the rock was formed. Find another fossil of the same species of dino somewhere else…that fossil was probably buried within a couple hundred thousand years of the first one, so now you have a good idea of how old the rock around the second fossil is, and the age of other fossils in that geological layer.
You can also use less precise methods relative to your precisely measured date. think of those methods like pacing out a distance. Errors add up over long distances, so trying to pace out the length of a mile might be pretty tricky. If your off by 10%, that’s a pair of football fields. Find a highway marker tell you that your standing at 1700 yards from your starting point…now you only need to measure the last 60 yards. Even if you’re wrong by a huge margin, the total error is small because you know most of the distance very accurately.
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