As the uranium in rocks decays, it emits subatomic particles and turns into lead at a constant rate.
Radioactivity also gave the history of life an absolute calendar.
By measuring the atoms produced by these breakdowns inside rocks, physicists were able to estimate their ages (right).
Hutton's theories were short on evidence at first, but by 1830 most scientists concurred that Noah's ark was more allegory than reality as they documented geological layering.
Using fossils as guides, they began to piece together a crude history of Earth, but it was an imperfect history.
Darwin had finally gotten the luxury of time he had craved.