During the ice age, the climate alternated between glacials and interglacials. Which description correctly matches their typical durations and temperature differences?

• A. Glacials last about 10,000 years and are 2–3°C cooler; Interglacials about 100,000 years and warmer
• B. Glacials last about 100,000 years and are about 5–10°C cooler; Interglacials about 10–20,000 years and near modern temperatures
• C. Glacials last 1 million years; Interglacials last 1,000 years
• D. Glacials and interglacials durations are highly variable and not well defined

Answer: (B)

The pattern being tested is the typical timing and warmth swings of glacials and interglacials seen in the Ice Age record. Glacials are long cold spells when large ice sheets expand; interglacials are shorter warm spells when ice recedes. The best-fitting description is that glacials last about 100,000 years and are about 5–10°C cooler than interglacials, while interglacials endure roughly 10,000–20,000 years and reach temperatures close to modern levels. This aligns with paleoclimate data from ice cores and sediments, which show long, pronounced cooling during glacials and shorter, warmer intervals in between.

Other timings described—glacials as short as 10,000 years or interglacials as long as 100,000 years, or the idea that durations are highly variable and not well defined—don’t match the well-established pace of these cycles.