Glottochronology — carbon-dating the words

Swadesh (1950s): a language's CORE vocabulary — the 100-200 most basic words (mother, water, two, hand) — is replaced at a roughly constant rate, so its loss is EXPONENTIAL: retention r^t with r about 0.86 per millennium. Sealed: 74% remain after 2,000 years, a ~4,595-year HALF-LIFE for basic vocabulary (https://narrowhighway.com/s/9c66f521565216319b7ab6cf3bca9314c18dfe3e9982b88459f714c61237c10f) — the identical decay math as carbon-14, which is why it is called linguistic dating. The linear misconception (lose the same NUMBER each era) sealed BROKEN (https://narrowhighway.com/s/e456b15c210b9675bfdb7813c725256cd2c52b267665b9cc4518a826c6019545): words decay by RATIO, like atoms, like a capacitor, like everything on the exponential spine. Honest grade: the METHOD is exact, the constant RATE is HEURISTIC and contested (borrowing and contact perturb it) — a trend, not a law, same class as the Phillips curve on the boundary map.