How do scientists know how old the Earth is?
Scientists say the Earth is about 4.5 billion years old. How could anyone possibly know that? Nobody was around to see it form. What method do they use to figure out the age of something that old? How confident are they in that number? Could they be off by a lot?
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I teach high school science and I get this question every year. The textbook explanation is a simplification — a useful one, but a simplification. The real answer involves stuff you'd cover in a college course, but I can give you the gist.
3 Answers
I teach high school science and I get this question every year. The textbook explanation is a simplification — a useful one, but a simplification. The real answer involves stuff you'd cover in a college course, but I can give you the gist.
I'm a physics grad student and this is one of my favorite questions to explain. The key insight is that our everyday intuition doesn't always apply at extreme scales — very small (quantum), very large (cosmological), or very fast (relativistic).
The honest answer is that scientists don't fully understand this yet. We have good models that make accurate predictions, but the 'why' underneath is still an active area of research. Anyone who tells you they have the complete answer is oversimplifying.
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