Fossil Age Estimator Calculator

This calculator runs two independent dating methods side by side so you can cross-check one against the other. The radiometric age comes from the decay equation t = t½ × ln(1 + D/P) / ln(2), where D and P are the measured amounts of daughter and parent isotope and t½ is the half-life of whichever system you pick — Carbon-14 (5,730 years, useful only out to roughly 50,000 years before the parent signal is too depleted to measure reliably), Potassium-Argon (1.25 billion years), Uranium-Lead (4.47 billion years, listed by the U.S. Geological Survey's published radiometric time scale as 4.5 billion years rounded), or Rubidium-Strontium (48.8 billion years) — all four half-lives matching the USGS's own currently accepted values. The formula assumes a closed system: no parent or daughter isotope has leaked in or out since the rock or fossil formed, which is rarely perfectly true in practice and is the single biggest source of real-world error in radiometric dating.

Separately, the stratigraphic age is a simple depth-over-rate calculation — sediment depth divided by sedimentation rate — that assumes a constant, uninterrupted deposition rate through the whole section, an assumption that erosion, hiatuses, or compaction can violate badly. The two ages are meant to be compared: strong agreement between them increases confidence in both. The calculator also reports percent parent remaining, half-lives elapsed, and a simplified geologic-era code derived from the radiometric age. The most common mixup is picking a dating system whose useful range doesn't match the sample's expected age — Carbon-14 saturates and becomes meaningless for anything older than about 50,000 years, so a "recent" fossil dated with Uranium-Lead will look nonsensically young.