Every layer of lake or bog sediment traps the pollen that rained down onto the water that year. Because different plants release pollen grains with distinctive shapes, counting hundreds of grains per layer under a microscope yields a "pollen percentage diagram" — the relative abundance of each taxon through time. Comparing those percentages against the pollen rain of modern vegetation of known climate (a "transfer function") lets palaeoecologists estimate past temperature and moisture without a single thermometer ever being there.
score(taxon, T, M) = weighted response to temperature T and moisture M
proportion(taxon) = score(taxon) / Σ score(all taxa) — softmax-style normalisation
age(depth) ← anchored by radiocarbon dates + tree-ring (dendrochronology) cross-checks
- Depth in record — scrub the core from the present (top, 0 yr BP) down to 12,000 years before present (bottom); the cylinder highlights the sampled layer and the ring of vegetation around it redraws to match.
- Auto-scrub — plays the record forward and back automatically, at the rate set by Scrub speed.
- Compare to modern (HRV) — overlays a translucent "modern baseline" ring so you can see how far the selected period's vegetation departs from today's — the core idea behind historical range of variability, the baseline conservationists use to judge how unusual current ecosystem states really are.
This record is a stylised, synthetic climate history (a Younger-Dryas-like cold snap near ~11,500 BP, a mid-Holocene warm optimum near ~6,000 BP, a Little-Ice-Age dip near ~300 BP) rather than a real core — it exists to show the mechanism, not to report a specific lake's data. Independent tree-ring chronologies (dendrochronology) are what let scientists cross-date and calendar-anchor a pollen sequence like this one to actual calendar years.