Age of Meteorites and the Earth
Lead from five meteorites falls on one line whose slope dates the Earth at 4.55 billion years.
How do you weigh the age of a whole planet? Clair Patterson did it by measuring lead — not in the Earth, but in meteorites, the leftover rubble of the day the planet was born.
The idea, unpacked
Some atoms are tiny clocks. Uranium slowly turns into lead — two kinds of uranium into two kinds of lead, each at its own steady, precisely known pace. So the longer a rock has existed, the more of these special leads it has accumulated. Measure how much, and you can read off the rock's age.
Patterson realised he didn't need the Earth itself: he could date the meteorites that formed alongside it, from the same cloud of dust, at the same moment. When he plotted the lead from several meteorites on a graph, the points lined up along a single straight line. The tilt of that line is the clock's reading — 4.55 billion years. And when he checked the Earth's own lead, it sat on the very same line, so the Earth is exactly as old as the meteorites.
Seven years in a clean room
Patterson began this as a graduate student and hit a wall: everywhere he looked, his samples were swimming in lead — from the air, the dust, his glassware, even the solder in the lab. The tiny amounts he was trying to measure kept drowning in contamination. So he built one of the world's first ultra-clean laboratories, scrubbing every surface and distilling his own acids, to win a reading he could trust. It took the better part of a decade. When the answer finally came — 4.55 billion years — it has barely moved since. But the lead he kept finding everywhere haunted him: there was far more of it than nature could explain. He spent the rest of his career proving it came from leaded gasoline, and fighting to get the lead taken out.
Why it mattered
For centuries the age of the Earth was guesswork, and the guesses ranged wildly — a few thousand years from scripture, a few tens of millions from the physics of a cooling planet, hundreds of millions from the thickness of rocks. Patterson ended the argument with one hard number, grounded in atomic physics and checkable by anyone. It gave evolution and geology the deep time they had always needed, and it placed our planet — and ourselves — correctly within the history of the universe.
Reading a tilted line
Imagine a row of identical hourglasses, all flipped at the same instant but each holding a different amount of sand. At any later moment, the fuller and emptier ones all reflect the same elapsed time — plot ‘sand fallen’ against ‘sand left’ and the points fall on one straight line that tilts further as the hours pass. Patterson's meteorites are those hourglasses; uranium is the sand running down into lead; and the tilt of the line they make is the age of the world.
Before and after
Hutton (1788) and Lyell (1830) argued the Earth was almost unimaginably old but had no way to count the years; Kelvin, using heat alone, insisted it was far younger and clashed with the geologists. The discovery of radioactivity by Curie (1898) and Rutherford (1911) handed science the clock that could settle it. Patterson read that clock to its limit. Two decades on, the same deep-time thinking framed Alvarez (1980), whose asteroid punctuated the long calendar Patterson had measured.