The primary evidence indicating that the Earth is approximately 4.6 billion years old comes from using the radiometric dating of early Earth rocks. This method relies on the decay of radioactive isotopes in minerals that form in rocks, allowing scientists to determine the age of those rocks and, by extension, the age of the Earth itself.
Specifically, dating techniques such as uranium-lead dating and the dating of meteorites (which are believed to have formed around the same time as the early Earth) have consistently provided ages in the range of about 4.5 to 4.6 billion years.
The other methods mentioned, such as adding up layers of rock strata or using carbon-14 dating, are less applicable to determining the Earth's age:
- Adding up the layers of rock strata is used to understand the geological history but does not provide a precise age for the Earth itself.
- Using carbon-14 dating methods is effective for dating organic materials and remains from more recent geological time (up to about 50,000 years) and is not suitable for dating the age of the Earth or early life forms that predate substantial amounts of carbon-14.
- Calculating the cooling rate of the Earth's mantle can provide information about thermal history but does not directly give an age for the Earth.
In summary, radiometric dating of early Earth rocks is the most accurate method for determining that the Earth is about 4.6 billion years old.
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