How Old Is The Earth?

How did scientists figure out Earth's age?

Through radiometric dating, which measures the radioactive decay of certain elements in rocks. According to NASA, the most reliable age estimates come from meteorites that formed at the same time as Earth, around 4.54 billion years ago. Specific isotopes like uranium-238 decay into lead at a known steady rate, so by measuring the ratios of parent and daughter isotopes in a rock sample, scientists can calculate exactly how long ago that rock formed.

What's the oldest thing on Earth?

Tiny zircon crystals from Western Australia, dated to about 4.4 billion years old, are currently the oldest known terrestrial materials. The oldest intact rocks are around 4.0 billion years old, found in northern Canada. Earth itself is older than its oldest surviving rocks, because plate tectonics, weathering, and impacts have erased or recycled most of the original crust. Meteorites that formed at the same time as Earth but never melted are the cleanest record of the solar system's birth.

How does Earth's age compare to the universe?

The universe is about 13.8 billion years old, so Earth formed when the universe was already roughly 9 billion years old. The Sun and the rest of our solar system are about the same age as Earth, having formed from the same cloud of gas and dust. Earth is roughly the third generation of stars and planets to form in our region of the galaxy, built from elements forged in earlier stars that lived and died before our Sun ever existed.

Is Earth's age really settled science?

Yes. The 4.54 billion year figure has been confirmed by multiple independent methods using different elements and different samples, all converging on roughly the same answer. Earlier estimates ranged wildly (Lord Kelvin famously calculated Earth was only 20 to 40 million years old based on cooling rates, before radioactivity was discovered), but radiometric dating in the 20th century put the question to rest. The margin of error today is about 1 percent.