Researchers from the U.S. Geological Survey studying ancient pollen and charcoal preserved in deeply buried sediments in Egypt’s Nile Delta have documented the region’s ancient droughts and fires, including a massive drought that happened approximately 4,200 years ago and is thought to have seen the demise of Egypt’s Old Kingdom.
“Humans have a long history of having to deal with climate change,” said Christopher Bernhardt, a researcher with the U.S. Geological Survey. “Along with other research, this study geologically reveals that the evolution of societies is sometimes tied to climate variability at all scales – whether decadal or millennial.”
“Even the mighty builders of the ancient pyramids more than 4,000 years ago fell victim when they were unable to respond to a changing climate,” said USGS Director Marcia McNutt. “This study illustrates that water availability was the climate-change Achilles Heel then for Egypt, as it may well be now, for a planet topping seven billion thirsty people.”
The researchers studied pollen and charcoal preserved in a Nile Delta sediment core that dates back 7,000 years. They wanted to determine whether changes in pollen would reflect conditions in ancient Egypt and the Middle East, specifically the droughts recorded in archaeological and historical records.
They also wanted to examine the presence and amount of charcoal in the core. Fire frequency often rises during times of drought, and fires are recorded as charcoal in the geological record.
The scientists hypothesised that that the proportion of wetland pollen would decline during times of drought and the amount of charcoal would increase.
And they were right.
The were massive decreases in the proportion of wetland pollen and increases in microscopic charcoal observed in the core during four separate instances from 3,000 to 6,000 years ago. Evidence showed large droughts some 5,000 to 5,500 years ago, another around 3,000 years ago, and one that is believed to be the abrupt and global mega-drought that took place some 4,200 years ago and is believed to have lasted for the better part of a century. It is believed to have had huge societal repercussions including famines, and is thought to have played a role in the end of Egypt’s Old Kingdom.
“Our pollen record appears very sensitive to the decrease in precipitation that occurred in the mega-drought of 4,200 years ago,” Bernhardt said. “The vegetation response lasted much longer compared with other geologic proxy records of this drought, possibly indicating a sustained effect on delta and Nile basin vegetation.”
The two smaller droughts are also recorded in human history – the first one started some 5,000 years ago when the unification of Upper and Lower Egypt occurred and the Uruk Kingdom in modern Iraq collapsed. The second event, some 3,000 years ago, took place in the eastern Mediterranean and is associated with the fall of the Ugarit Kingdom and famines in the Babylonian and Syrian Kingdoms.
“The study geologically demonstrates that when deciphering past climates, pollen and other micro-organisms, such as charcoal, can augment or verify written or archaeological records – or they can serve as the record itself if other information doesn’t exist or is not continuous,” said Horton.