The Sahara desert turns into a green expanse every 20 years. The discovery of MIT

    The Sahara desert turns into a green expanse every 20 years. The discovery of MIT

    The Sahara changes from a desert to a green expanse every 20 years. I study.

    He is about to end up run over, his mother saves him

    From desert to green plain and vice versa: the area radically changes its appearance every 20 thousand years in sync with monsoon activity





    The Sahara Desert is one of the harshest and most inhospitable places on the planet, covering much of North Africa amidst thousands of square miles of rocks and windswept dunes. But it hasn't always been so desolate and barren. In fact, primitive rock paintings and fossils excavated in the region suggest that the Sahara was also a relatively verdant oasis, where human settlements and a variety of plants and animals thrived.

    This is confirmed by researchers from MIT, who in a new study have analyzed the dust deposited off the coast of West Africa in the last 240 years and have discovered that the Sahara and North Africa in general have practically fluctuated between wet and dry climates every 20 years. A sort of climatic "pendulum" mainly driven by changes in the Earth's axis as the planet orbits the sun, which in turn affects the distribution of sunlight between seasons.

    For North Africa, this is likely when the Earth is tilted to receive the maximum sunlight With each orbit around the sun, this increased solar flux intensifies the region's monsoon activity, which in turn makes the Sahara wetter and greener. As the planet's axis swings to an angle that reduces the amount of incoming sunlight, monsoon activity weakens, producing a drier climate similar to what we see today.

    "Our findings suggest that North African climate history is dominated by this 20.000-year rhythm, which goes back and forth between a green and dry Sahara," says David McGee, associate professor in MIT's Department of Earth, Atmospheric and Planetary Sciences. We believe this is a useful time series to examine in order to understand the history of the Sahara desert and what times would be optimal for humans to colonize the Sahara desert ”.



    A systematic review

    Northeast winds collect hundreds of millions of tons of Sahara dust each year, depositing much of this sediment in the Atlantic Ocean off the coast of West Africa. Layers of this dust, accumulated over hundreds of thousands of years, can serve as a geological chronicle of the climatic history of North Africa: Dense layers of dust may indicate arid periods, while those containing less dust may indicate wetter eras.

    Scientists analyzed sediment cores excavated from the ocean floor off the coast of West Africa, which contain layers of ancient sediment deposited over millions of years. Each layer may contain traces of Saharan dust and the remains of life forms, such as tiny plankton shells.

    The researchers, led by lead author Charlotte Skonieczny, examined layers of sediment deposited over the past 240 years and, analyzing each layer for traces of dust, measured the concentrations of a rare isotope of thorium to determine how quickly dust was accumulating on the surface. seabed.

    Thorium is produced at a constant rate in the ocean from very small amounts of radioactive uranium dissolved in seawater and quickly attaches itself to sinking sediments. Consequently, scientists can use the concentration of thorium in sediments to determine the rate at which dust and other sediments accumulate on the seafloor: during periods of slow accumulation, thorium is more concentrated, while in times of rapid accumulation, the thorium is diluted.

    “What we found is that some of the dust spikes in the nuclei were due to increased deposition of dust in the ocean, but other spikes were simply due to the dissolution of the carbonate and the fact that during the ice ages, in this region, the ocean was more acidic and corrosive to calcium carbonate. It may seem like there is more dust deposited in the ocean when in reality there isn't. "



    The researchers realized that the Sahara oscillated between humid and arid climates every 20 years, in sync with the region's monsoon activity and the periodic tilt of the Earth.

    Read also

    • The Sahara Desert has advanced 10% in the past century
    • It snows in the Sahara desert: the unusual spectacle of the whitewashed dunes

    Germana Carillo
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    The Sahara desert changes its appearance every 20 thousand years

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