We now know that Earth is about 4.5 billion years old, but thanks to the time dilation effects of gravity, the planet’s core is about two years younger than that.
How did we calculate the age of the Earth?
Initial attempts to calculate the age of the Earth using science were somewhat unsatisfactory. Physicist William Thomson (aka Lord Kelvin) proposed an idea in 1844 for how to measure the age of the Earth. He initially assumed that the Earth was a large molten blob in space. He thought he could calculate the age of the Earth itself, by looking at how long it would take for the planet to cool enough to become what it is now.
Years later, he made this calculation and estimated that the Earth was 20 – 400 million years old. This estimate contradicted many things, including geology, Darwin’s ideas about how long animal evolution would take, and his belief that the Sun was only about 20 million years old.
Thomson’s estimates were calculated before radiometric dating, which gives us a much more accurate way to find the age of rocks.
What is radiometric dating?
“The age of Earth and Moon rocks and meteorites is measured by the decay of long-lived radioactive isotopes of elements naturally found in rocks and minerals, and these isotopes decay into stable isotopes of other elements with half-lives of more than 700 million to 100 billion years,” explains on the website of the U.S. Geological Survey. It is used to measure the humidity.”
While using radiometric data gives a much more accurate idea of how old the rocks are, dating Earth rocks can only give the minimum possible age of the Earth. The oldest rock we’ve ever found from the Acasta Gneiss Complex in northwest Canada is about 4.02 billion years old. This gives us a minimum age since we can safely assume that it is no younger than Earth’s oldest rock. However, it is not possible to estimate the maximum age of the planet with this method alone, unless you analyze every rock on the planet. The possibility that the oldest rocks on Earth may have slipped into Earth’s mantle also makes it difficult to determine their age.
Instead, the scientists studied rocks from the Moon and other bodies in the solar system where this movement of change was not a problem. Geochemist Clair Cameron Patterson studied meteorite samples containing abundant lead isotopes taken from a rock that fell in Arizona in 1953 and used for radiometric dating. These specimens have been dated to between 4.53 billion and 4.58 billion years ago.
Further measurements of space rocks and further study of how the solar system evolved have allowed us to improve our predictions.
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