How old is the Earth, and how do we know?
4.54 billion years, with an uncertainty of about 1 percent, roughly 50 million years. The figure comes from radiometric dating: certain elements decay into others at rates that are fixed, measured, and unaffected by heat or pressure, so a mineral's ratio of parent to daughter atoms is a clock that started when the mineral formed.
Because Earth's earliest surface was recycled by plate tectonics, the age is anchored partly off-planet: meteorites, leftover raw material from the solar system's formation, date to 4.56 billion years, and moon rocks agree. On Earth, zircon crystals from Australia have been dated beyond 4.3 billion years. The key strength is independence: uranium-lead, potassium-argon, and rubidium-strontium decay systems act as separate clocks, and they converge on the same answer, which is how science distinguishes a measurement from a guess.
The number was first nailed down in the 1950s by geochemist Clair Patterson, who along the way discovered industrial lead contamination and helped get leaded gasoline banned.
4.54 billion years, give or take about 1 percent, measured by radiometric dating of meteorites and ancient minerals. Multiple independent atomic clocks all land on the same answer.
- USGS geologic age dating
- National Academy of Sciences
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https://frequentlyaskedquestions.us/q/how-old-is-the-earth/Everybody Asks. (2026, July 28). How old is the Earth, and how do we know? https://frequentlyaskedquestions.us/q/how-old-is-the-earth/“How old is the Earth, and how do we know?” Everybody Asks, 28 July 2026, https://frequentlyaskedquestions.us/q/how-old-is-the-earth/.“How old is the Earth, and how do we know?” Everybody Asks. Last modified July 28, 2026. https://frequentlyaskedquestions.us/q/how-old-is-the-earth/.This page summarizes the primary sources listed above. For academic or encyclopedic work, cite those primary sources directly wherever possible.