New research indicates that the Sahara, the barren and desert covered region of northern Africa, was once lush and was filled with vegetation and lakes.
You may be surprised to hear that cave paintings in the Sahara depict hippos drinking in waterholes and large herds of elephants and giraffes. A strange finding perhaps, in such a lifeless place, but new research indicates that the wide belt of barren desert in northern Africa has not always been so barren.
Researchers from Columbia University and MIT have discovered that the climate in Sahara was quite lush between 11,000 and 5,000 years ago, a period known as the African Humid Period. On either side of that period, the region has been a desert, as we know it today. The most amazing fact about the change in northern Africa is how abruptly it occurred. The researchers believe the region reverted into a desert in just a generation or two.
Dust plumes like this one give an indication of how arrid Sahara is
This research comes as a result of a 2007 research expedition, during which researchers from Columbia and Woods Hole Oceanographic travelled to the region to collect 10-foot long, cylindrical sediment samples off the coast of Africa. David McGee, assistant professor at MIT’s Department of Earth, has been analyzing the samples, which contain some 30,000 years worth of dust and sediment.
Windblown dust, which is present in the samples, gives a very good indication of the aridness of the Sahara at different times. Periods when a lot of dust accumulated indicates dry times, while lower accumulation indicates a lusher Sahara. To analyze how much dust was accumulating, McGee used a process called Thorium-230 normalization. Thorium-230 is a product of natural radioactive decay of uranium, and it sticks to dust from Sahara. The oceans have a fairly constant production rate for Thorium-230, so by measuring which parts of the sediment samples have more Thorium it’s possible to determine when more dust was being collected. In periods with a lot of dust, the Throium-230 levels are lower.
Natalie Mahowald, a professor at Cornell University specializing in Earth and atmospheric sciences, says the research has produced better estimates of dust buildup than ever before "Dust is one of the most important aerosols for climate and biogeochemistry," says Mahowald, "This study suggests very large fluctuations due to climate over the last 10,000 years, which has enormous implications for human-derived climate change."