Not a fact anymore

Earth is only tens or hundreds of millions of years old.

What we know now

Earth formed about 4.54 billion years ago. Radiometric dating of meteorites, lunar material, and Earth's oldest minerals and rocks all support this age.

Why it changed

Early estimates treated Earth mainly as a body cooling from a hot beginning. They did not account for radioactive heat or the way heat moves through the mantle. Radioactivity and radiometric dating later provided reliable clocks for deep geological time.

Status: Corrected
Category: Earth Science
Accepted for: ≈75 years
Accepted approximately: Mid to late 19th century
Changed approximately: 1890s–1950s

Kelvin’s estimate was not a casual guess. It was a serious calculation based on the physics then available, but some of its assumptions were incomplete, especially the omission of radioactive heat and mantle convection.

Geologists had already argued that Earth must be extremely old. Isotope dating eventually supplied a reliable numerical age.

Evidence

Sources and what they establish

Previous belief

Powell Expedition—Geologic Time. Then and Now.U.S. Geological Survey
Describes Lord Kelvin's estimates of roughly 20 to 400 million years.

Current evidence

When in Earth's history did Yellowstone's volcanism begin?U.S. Geological Survey
States that meteorite dating gives Earth an age of approximately 4.54 ± 0.05 billion years.
Geologic Time: Radiometric Time ScaleU.S. Geological Survey
Explains how radioactive decay provides numerical ages for rocks and geological events.

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