Cold War nuclear testing doubled atmospheric carbon-14 by 1963. Every cell dividing during those decades incorporated the excess isotope into its DNA. The ratio in a cell's DNA identifies when that cell last divided — a date written in the cell itself, by an event the cell had nothing to do with.
Your body is not one thing located at one time. Set your birth year below and see where each tissue type sits in the historical record. Fast-turnover tissues live near the present. Neurons are anchored at birth. In between are decades of stratification.
Individual cells cannot be dated in a living person — the method requires extracting and hydrolyzing DNA from tissue samples, then measuring C-14 by accelerator mass spectrometry. The turnover rates shown here are population averages from cohort studies; individual cells vary. Heart muscle renewal is contested: some cardiomyocyte renewal studies report near-zero rates in adults, while Spalding's 2009 bomb pulse study found measurable turnover. The model uses ~0.7% per year as a representative estimate.
The curve itself extends slightly below zero after 2017: fossil fuel combustion has diluted atmospheric C-14 (the Suess effect) such that the bomb signal is now almost fully absorbed. Tissues born today will look slightly depleted, not enriched.
The interesting ambiguity: a tissue reading of 200‰ could place cells in either 1965 or 1980 — two different moments on the ascending and descending limbs. In practice, researchers resolve this using the person's age to select the correct limb. The pulse is a clock with two hands pointing different directions; context tells you which one to read.