<![CDATA[Researchers analyzing marine sediments have been able to pinpoint rainfall patterns from the so-called “Green Sahara,” the 6,000-year period of time when the desert was awash in plant and animal life. A press release from the University of Arizona announced the efforts of its researchers in publishing a new study describing the desert as it would have looked from between 11,000 and 5,000 years in the past. The Green Sahara was home to modern humans living off the land as hunter-gatherers thanks to annual rainfall levels that would have been 10 times higher – anywhere from 10 to 40 inches of rainfall a year, university researcher Jessica Tierney remarked. It has been known for some time that the Green Sahara existed. However, Tierney and the rest of the research team are the first to provide an uninterrupted record of rainfall in the region up to 25,000 years ago. The associate geosciences professor added that previous archaeological evidence suggested human migration in the region was integrally linked to rainfall figures, but the new data gathered by her team provides much greater detail. The continuous rainfall record was able to provide corroborating evidence of a “dry spot” during the Green Sahara, a period of around 1,000 years starting about 8,000 years in the past. The dry spot prompted human migration from the region; its end brought humanity back into the Sahara. The interesting part, Tierney said, is that the humans who came back after the dry period ended were a completely different culture. Instead of the former hunter-gatherers, they would have been involved in raising cattle, with the rainfall record providing climate context for this transition in lifestyle and occupation within the western Sahara, the researcher added. Previous investigations into the relative amount of life the Sahara supported in the past left only a partial picture of history. Normal methods for learning about past climate, including the examination of ancient lake sediments, were obviously impossible with the Sahara as these lakes would have dried up thousands of years in the past, their sediments being dispersed with the desert winds. Instead, Tierney and her team turned to marine sediment samples taken off the West African coast at several different sites. These sites were chosen on a north-south axis and stretched some 800 miles from end to end, from Morocco to Mauritania. These core samples were thus able to reveal the extent of the Green Sahara as well as ancient rainfall patterns. The key came in examining the chemical composition of the changes that a leaf’s wax undergoes, which will differ depending on the amount of moisture the plant receives while growing. This leaf wax washes into the ocean, becoming preserved in marine sediment and leaving a clear record of terrestrial climate conditions, Tierney remarked. The results were a determination of the region’s ancient rainfall patterns as well as some information as to the types of flora that would have grown there. The research study, which appears in the journal Science Advances, can be found here Image courtesy of Peter deMenocal]]>
Researchers Pinpoint Rainfall Patterns of Ancient Sahara
