With their awe-inspiring feats of architecture—the pyramids—ancient Egyptians left their mark on the world. But a new study confirms that the world also left its mark on the Egyptians.

Benjamin Horton, an associate professor in the Department of Earth and Environmental Science, and his former graduate student and current U.S. Geological Survey researcher Christopher Bernhardt, along with Smithsonian Institution scientist Jean-Daniel Stanley used fossil evidence from plants and microscopic charcoal to document an ancient “mega-drought” that occurred more than 4,000 years ago. The drought likely contributed to the fall of Egypt’s Old Kingdom, which ruled over an era widely known as “the Age of the Pyramids.”

Previous studies had identified historical and archaeological evidence of the drought, but Horton, Bernhardt, and Stanley wanted to see if they could find a record of the prolonged stretch of extreme aridity through another source. They chose to look for signs of ancient drought in a sediment core taken from the Burullus Lagoon in Egypt’s Nile Delta.

Using the sediment sample, which represents 7,000 years of environmental change, the researchers examined how proportions of charcoal and pollen from wetland plants varied through the layers. Increases in microscopic charcoal—markers of fire—and declines in levels of wetland pollen would indicate periods of drought, when the Nile River’s flow was low, they reasoned.

Their analysis of the sample indicated four periods between 3,000 and 6,000 years ago during which wetland pollen proportions declined while charcoal levels jumped. The radiocarbon dates of these layers corresponded with known droughts that occurred in the region. The most notable drought, dating to 4,200 years ago, is believed to have led to widespread famines and social discord in Egypt and other societies in the Mediterranean region.

The study suggests that paleoecological records of environmental entities such as pollen and charcoal “can augment or verify written or archaeological records,” says Horton, “or they can serve as the record itself if other information doesn’t exist or is not continuous.”

Such a tool may allow geologists to partner with archaeologists and historians to expand our understanding of how changes in climate have shaped human history, going back thousands of years.