Sahara Desert changed from wet to dry every 20,000 years, study

Study shows the Sahara swung between lush and desert conditions every 20,000 years, in sync with monsoon activity.

A new analysis of African dust reveals the Sahara swung between green and desert conditions every 20,000 years, in sync with changes in the Earth’s tilt.
A new analysis of African dust reveals the Sahara swung between green and desert conditions every 20,000 years, in sync with changes in the Earth’s tilt.

The Sahara Desert is known as one of the hottest, driest and most desolate areas in the world. It covers about 9.3 million square kilometers across North Africa.

Primitive rock paintings and fossils excavated from the region suggest that the Sahara was once a relatively verdant oasis, where human settlements and a diversity of plants and animals thrived.

Now, MIT scientists have analyzed dust deposited off the coast of West Africa over the last 240,000 years and found that the Sahara, and North Africa in general, has swung between wet and dry climates every 20,000 years.

The evidence showed that at times, the Sahara changed to a very wet climate. This permitted plants and animals to develop and grow and led to the creation of human settlements.

Scientists discovered more evidence of this changing climate. They examined dust gathered from the coast of West Africa over the past 240,000 years. The outcomes suggest that during that period, the Sahara’s climate kept changing between wet and dry about every 20,000 years.

David McGee, an associate professor in MIT’s Department of Earth said, “the new evidence supports the idea that the area’s climate repeatedly kept changing over the years. Our results suggest the story of North African climate is dominantly this 20,000-year beat, going back and forth between green and dry Sahara.”

Scientists reported that the back and forth climate changes were mainly driven by changes in the Earth’s axis as the planet orbits the sun. This process affects the amount of sunlight between seasons. The research suggests that every 20,000 years, the Earth receives more intense summer sunlight.

At the point when the Earth’s axis changes once more, the measure of sunlight is reduced. This season change happened consistently every 20,000 years, the examination found. The other piece of the season delivered rainstorm conditions, bringing about a wetter, greener, plant-rich condition. At the point when the rainy activity debilitates, the atmosphere winds up hot and dry, similar to the Sahara remains today.

Though, the study was based on dust samples collected from ocean sediment. They reported that hundreds of millions of tons of Saharan dust had built up over hundreds of thousands of years in the Atlantic Ocean bottom off the coast of West Africa.

An examination of the dust buildup allowed the analysts to find out about the Sahara Desert’s atmosphere history. The examples contained layers of ancient residue developed more than a large number of years. Each layer could contain hints of Saharan dust and in addition the remaining parts of life forms.

Scientists used this information to estimate over what time period the dust had built up. This led to the overall finding that the Saharan changes from wet to dry climates happened every 20,000 years.

The new study suggests that the area’s climate has “shifted between grasslands and a much wetter environment, and back to dry climates, even over the last quarter million years.

The study is published in Science Advances.