The desert turns into fertile land every 21 thousand years!

Arabia Weather - It's hard to imagine, but the Sahara Desert was a green forest a few thousand years ago.

The desert turns into fertile land every 21 thousand years

It may seem as if the sand dunes and rocky plateaus of the Sahara are as old as time, but that could be far from the truth. As a new study shows, this vast strip of North Africa turns from barren desert to lush green forests every 21,000 years or so.

The last period when the Sahara was a green forest occurred between 15,000 and 5,000 years ago. This latest research confirms that this was not just a curious blob, but part of a cyclical transition that changed the region from arid to wet about every 21,000 years.

“The cyclical transformation of the Sahara into different ecosystems and forests is one of the most significant environmental changes on the planet,” said Dr. Edward Armstrong, the study's lead author and a climate scientist at the University of Helsinki and the University of Bristol, in a report.

“Our study is one of the first climate modeling studies that simulates African wet periods at a similar magnitude to what paleoclimate observations indicate, and reveals why and when these events occur.”

The new research looks to better understand the so-called "North African Humid Periods" over the past 800,000 years using a recently developed climate model.

Their work confirmed the idea that periodic wet phases in the Sahara were driven by changes in the Earth's orbit around the sun. It is generally agreed that the " greening " of the Sahara Desert is due to the Earth's oscillation on its axis, which affects seasonality and determines the amount of energy this part of the planet receives. This ultimately affects the strength of the African monsoon, which helps control the amount of vegetation spread across this vast region.

However, their work also suggests that this cycle may be influenced by distant ice sheets at high latitudes in the Northern Hemisphere. Wet periods did not occur during ice ages when most of the Earth's high latitudes were covered by thick ice sheets.

Experts speculate that these ice sheets helped cool the atmosphere like a refrigerator, limiting the African monsoon system and suppressing the growth of plant life in the Sahara.

The cyclical shift in North Africa is not only a big problem for the Sahara, but it also has huge implications for our story. After all, some of humanity's greatest early achievements – migrations out of Africa – were largely dictated by the condition of the Sahara. Depending on his “mood”, it can serve as a harsh obstacle or a welcoming path.

The gate was open when the desert was green, and it was closed when deserts prevailed

“The Sahara region serves as a gateway that controls the spread of species between North and sub-Saharan Africa, and within and beyond the continent,” explained Mika Talavara, co-author and assistant professor of hominin ecology at the University of Helsinki.

The gate was open when the desert was green, and it was closed when deserts prevailed. This alternation between wet and arid phases has had serious consequences for the dispersal and evolution of species in Africa. Being able to model wet periods in North Africa is a major achievement and means we are now better able to model human distributions and understand the evolution of our species in Africa.

Source: iflscience

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