If you’re wondering who we can thank for radiometric dating—the technique that lets us peer deep into Earth’s past—look no further than Bertram Boltwood. Around 1907, Boltwood used uranium–lead dating to calculate the ages of rocks, estimating the Earth to be at least 2 to 3 billion years old. That may not seem bold now, but back then, it was heresy to young-Earth assumptions still lingering from religious tradition.

His work stood on the shoulders of giants like Henri Becquerel, who discovered radioactivity in 1896, and Ernest Rutherford, who refined the exponential decay law. But it was Boltwood who applied this radioactive decay as a clock embedded in stone.

Later, Arthur Holmes refined these methods, pushing Earth’s estimated age to a now widely accepted 4.54 billion years.

Radiometric dating changed everything—it gave us a reliable, testable way to measure geological time. In a world teeming with myths and metaphors, this was a milestone of rational clarity. It’s a perfect example of how the universe whispers its secrets if you just know how to listen.