الوضع الليلي
3:45:12 
2023-09-26 
1999
Our planet has changed a lot over billions of years, from the location of the continents to the composition of the atmosphere.
A new study has looked in detail at the history of the Sahara Desert, which was not always a barren wilderness.
Researchers from Finland and the United Kingdom reconstructed the cyclical transformations of the Sahara over a period of 800,000 years, using a new climate model, which enabled the team to fill some gaps in what we know about the history of the Sahara region.
“The cyclical transformation of the Sahara desert into savannah and forest ecosystems is one of the most significant environmental changes on the planet,” says climate scientist Edward Armstrong, of the University of Helsinki in Finland. “Our study is one of the first climate modeling studies that simulates African humid periods on a scale similar to what observations indicate.” "The ancient climate, and reveal the cause and timing of these events."
The researchers focused in particular on what is known as the African Humid Period, when the African continent was wetter and greener than it is today.
The developed modeling supports a long-standing hypothesis that African wet periods are driven by the Earth's orbital precession: the way it wobbles on its axis over a 21,000-year cycle, which in turn affects the variation between the four seasons and the strength of the African monsoon and meteorological system.
The precessions indicate warmer summers in the Northern Hemisphere, more intense monsoons across West Africa, and therefore more rain across the Sahara.
The study also revealed that during ice ages - with giant glaciers covering high latitudes - the effects of oscillation in Earth's orbit were somewhat canceled out, keeping northern regions colder and restricting the African monsoon.
It is worth noting that knowing when the Sahara Desert was wet, green, and inhabited by animals such as hippos, can teach us more about the spread of humanity around the world.
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