I keep hearing 4.6 to 4.7 billion years old for the age of the planet. Usually proved by dating meteorites. However, you never hear of anything older than this. Even though it [appears](https://world-nuclear.org/information-library/nuclear-fuel-cycle/uranium-resources/the-cosmic-origins-of-uranium.aspx) that the uranium that we use to date the planet was formed 6.5 billion years ago from the previous generation of stars.
The dust cloud that contained all the material that makes up both the planet and asteroids was here long before that.
So, my question is this, How did we settle on 4.6 – 4.7 billion years old for the age of the planet when all the materials were here long and coalescing before that? Did we just not cosider it a planet before the formation of the sun?
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Edited for corrections and clarity (hopefully). I can’t remove solar system from the subject line.
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When Rocks solidify from magma their composition crystalises and we can use isotopes that got within them to get estimates of age. Uranium and Potassium are two isotopes that decay very slowly into other isotopes. By measuring how much decayed isotope there is within the rock compared to undecayed isotope, we can get a rough age. The oldest crystalized rocks are around 4 billion years old. Which means there must have been a planet with a molten core before that for the rocks to form from.
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