What is the best guess to how old the earth is?

Answer 1

100 years old --

That's a stupid answer, the best guess is hundreds of millions of years old. How could the Italian Renaissance of happened before the Earth began?

There is no certain answer to your question. But we can all say this. It's very, very old.

.Answer 2

we don't have to guess. Dating by radiometric techniques gives an age of 4.5x109 years. This value is accepted by most authorities. It agrees with the age of meteorites, and approx with the age of our Sun.

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