Answers at the Bottom of the Ocean
During past glacial periods, oceans were much lower than they are today, because most of the water on earth was trapped in ice. By drilling deep into the ocean floor, scientists can examine dust, chemicals, and fossils to determine previous climates.
Cross-section of a core drilled in the Mediterranean Sea. Layers of dust, sediment, fossils (plants and animals), volcanic ash, and salt left behind by an evaporated sea. (Image from the Integrated Ocean Drilling Program). Source: A Record from the Deep: Fossil Chemistry | NASA