While much of the historical climate record comes from ice cores, it's possible to get useful information from drilling in other kinds of material. Last year, scientists in Antarctica pulled an ice core reaching back 740,000 years -- the most ancient found up to that point. But last month, researchers retrieved lake bed sediment cores from Lake Malawi with samples going back further than any previous cores of any type -- 1.5 million years.

"The lake has restricted circulation and virtually no oxygen at the bottom, so each year seasonal deposition of sediment creates a pattern like tree rings," King said. "With the cores we collected we'll be able to look at very old records of climate data simply by counting and analyzing the layers."

The researchers [...] chose to drill Lake Malawi because its unique location and geology will enable them to reconstruct a high-resolution, tropical climate history stretching back through the time when massive ice sheets periodically covered high-latitude North America and Eurasia.