🪨 How Archaeologists Actually Date Things

About this simulation

No single dating method covers the whole span of human and geological history. This simulation lays out a logarithmic timeline — from 10 years to 5 million years — and shows, as three glowing lanes, exactly where each major absolute-dating method works and where it runs out of road. Drag the sample-age slider and watch which methods light up.

How it works

• Dendrochronology — counting and cross-matching annual tree rings gives calendar-exact ages, but only as far back as continuous, overlapping ring chronologies reach (roughly 14,000 years with bristlecone pine and oak master chronologies).
• Radiocarbon (¹⁴C) dating — measures the decaying fraction of carbon-14 (half-life 5,730 years) left in once-living material. After about 8–9 half-lives (~50,000–55,000 years) too little ¹⁴C remains to measure reliably — the sample cube on the right dims to represent this.
• Potassium-Argon / Ar-Ar dating — measures argon-40 gas that accumulates from the radioactive decay of potassium-40 (half-life 1.25 billion years) trapped in volcanic minerals. It needs enough time for measurable argon to build up, so it is normally used from about 100,000 years old up to billions of years — it comfortably outlives every other method on this chart.
• The overlap between methods (and cross-checks against ice cores, varves, and other chronologies) is exactly why the same site is often dated more than one way.

Controls

• Sample age — sets the age (years before present) of the hypothetical sample, on a logarithmic scale from 10 to 5,000,000 years.
• Highlight method — dims the other lanes so you can focus on one dating method's range.
• Auto-sweep — animates the sample age sliding across the whole timeline.
• Show range labels — toggles the floating method-name and tick labels.
• Drag to rotate, scroll to zoom, ↺ resets the camera.

Did you know?

The potassium-argon particle count and tree-ring counts shown here are scaled for legibility, not to real proportions — real argon accumulation at these timescales is far too small to draw as literal bubbles, and a real 14,000-ring disc would be unreadably dense at this size.