Varves

Layered sediments in glacial-fed lakes were studied by counting the varves (Swedish for "layers") and estimating a glacier's age in (12,000 years) with considerable accuracy. This discovery was pivotal in identifying seasonal patterns in sediment deposition and their correlation with glacial and interglacial periods.
 Gerard Jakob de Geer Sweden 1878 Varves

Layered sediments in glacial-fed lakes were studied by counting the varves (Swedish for "layers") and estimating a glacier's age in (12,000 years) with considerable accuracy. This discovery was pivotal in identifying seasonal patterns in sediment deposition and their correlation with glacial and interglacial periods.