He walks through how ice core data from Greenland captured the Younger Dryas climate signal with far greater precision than the earlier pollen studies from Holland. Ice layers accumulate more consistently and preserve finer detail than lake sediments, which vary based on local hydrology. During drought years, reduced rainfall means less runoff and thinner sediment layers at the lake bottom, much like how trees produce narrower rings in dry conditions. This variability makes lake sediments a less reliable archive compared to ice, where each annual layer locks in atmospheric conditions with remarkable consistency. The Greenland record didn't just confirm what the pollen showed: it revealed the event in sharper focus, with timing and magnitude that sediment cores simply couldn't match.