Sorry I know people have asked similar questions before but I’m trying to find out how we know earth is ~4.5b years old and all the explanations are like “this is a vague explanation of what radiometric dating is and it says it’s about 4.5b years old”… which doesn’t really tell me anything about how we know it’s 4.5b. It’s not like we’ve existed for that long that we can have someone confirm that yeah, it’s billions of years old.
I’m not some religious person that doesn’t believe in science but I feel like it’s normal to carry a little bit of doubt in some of these things until you fully understand it, right?? I promise I’m happy to listen to any explanation as long as you remember that I do not study anything like this so any explanation that assumes I have knowledge in this subject matter is gonna mean nothing to me 🙁
In: Planetary Science
We can use math to calculate precisely how long it takes radioactive isotopes to lose exactly half of their energy and we call that number their “half life”. Using this, we can excavate various examples of these naturally occurring isotopes and based on exactly how radioactive they remain we can say they have gone through a certain number of these half-life cycles since they were originally created through whatever various natural processes created them. We have a fairly reasonable assurance that our methods of measuring and calculating these values is accurate but it’s not 100% impossible that some new discovery will alter our perception of how this works and change our reasoning about how many years ago something happened.
Some types of materials in the earth’s crust decay over time. We know the rate of decay. By looking at how much a particular material has decayed, we know when the material was originally deposited.
It matches all other simpler, mechanical dating techniques, such as tree rings, ice cores, varves, etc.
It’s like having a wind up clock that was fully wound up at the start, but has now run down half way. If you watch how much time it takes per turn and how many turns the spring can take, you can figure out how long ago it was fully wound. Sure, that doesn’t mean you were there at the beginning, or that someone didn’t set it up in a way to fool you. But if the time matches up with other evidence that it was two days ago, you’ve put together a good argument that is likely to be true
the principle is as follows – if I show you a tape measuret, being one meter. and I measure your step distance with it, and it corresponds to your step distance, you will no doubt agree with – “the distance of one of your steps is approximately 1 meter.”
now I ask you to walk 5 steps. I measure the distance, and show you that indeed it is approximately 5 meters (every step is slightly different, after all). again confirming – your step distance is approximately 1 meter, because 5 steps is 5 meters.
Now, I ask you to take 100 steps. What will the distance be? You should not need me to 100% accurately measure the distance to be able to tell you “it will be about 100 meters, with an error margin”.
Radiometric dating follows the same line of proof logic. We show through multiple small steps that the principle, the mechanism, is valid, and therefore we can use the principle to determine larger steps. only drawback being a larger amount of possible error.
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