Solved cryptogram

Uranium decays so slowly that much of what was here when Earth formed has yet to break down.

Chemistry Facts, sourced to Royal Society of Chemistry.

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What it means

The common isotope has a half life close to the age of the Earth itself, so a little under half of the original stock is still sitting in the rocks. That slow, steady decay is also a clock. Comparing uranium with the lead it turns into is how the age of the Earth was first established at roughly four and a half billion years, and the method has held up.

The claim comes from Royal Society of Chemistry.

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