Ancient Cave Discovery Reveals That 8,000 Years Ago, the Sahara Was Green

Scitech Daily ^ | March 10, 2025 | University of Oxford

[Red Badger]

Photo of a (currently) dry, dusty cave south of the Atlas mountains. In the past, water was flowing down this large stalagmite formation. We date tiny pieces of stalagmite (~0.25g) to establish when the cave was wet in the past. Credit: Ben Lovett

Analysis of Moroccan stalagmites reveals that the Sahara received increased rainfall between 8,700 and 4,300 years ago, supporting early herding societies. This rainfall, likely driven by tropical plumes and monsoon expansion, narrowed the desert, improved habitability, and facilitated human movement.

Analysis of stalagmite samples from caves in southern Morocco has revealed new details about past rainfall patterns in the Sahara Desert. Researchers from the University of Oxford and the Institut National des Sciences de l’Archéologie et du Patrimoine found that rainfall increased between 8,700 and 4,300 years ago, significantly influencing ancient herding societies. Their findings are published in Earth and Planetary Science Letters.

Stalagmites—rock formations that grow upward from cave floors—serve as valuable records of past climate conditions. Their formation requires rainwater to percolate through soil and drip onto the cave floor, meaning their presence indicates historical rainfall. The discovery of stalagmites near the edge of the world’s largest hot desert provided researchers with an opportunity to reconstruct past precipitation trends.

By analyzing trace amounts of uranium and thorium in the stalagmites, the researchers were able to determine when these formations grew, which in turn pinpointed periods of increased rainfall. Their findings confirm that the Sahara experienced wetter conditions during the African Humid Period, between 8,700 and 4,300 years ago.

“It is fabulous to see this research published after years of careful study. It was exciting to find and explore caves in southern Morocco during my fieldwork in 2010. And it is very rewarding that our measurements and interpretations fit so well with archaeological and environmental records from the wider region,” says Dr. Julia Barrott, study co-author, Impact and Learning Officer and Research Fellow at the Stockholm Environment Institute, Oxford.

Climatic Impact on Early Societies

This time period coincides with a rise in the number of Neolithic archaeological sites in the region south of the Atlas Mountains, which then plummeted when arid conditions resumed. The research team believes that this highlights the importance of a favorable climate on these early pastoralist societies, which relied on rainfall for their livestock.

ASD-1 is an example stalagmite used in our study, from a cave found by Dr. Julia Barrott during her 2010 fieldwork. We are careful to work with samples that are already broken from natural processes, e.g. by earthquakes or by rock fall within the cave. Stalagmites grow from bottom to top with banding similar to tree rings. Accurate chronology shows that the sample started to grow shortly before 6000 years ago. Credit: Dr. Julia Barrott

But the impact was not just local; the South-of-Atlas region is significant because the land slopes southwards into the heart of the Sahara. As a result, enhanced rainfall during this period refilled major aquifers and increased river flow in the desert. This would have made it easier for populations to travel into this inhospitable environment to connect with other groups and exchange both goods and knowledge.

The research team also analyzed the amounts of different oxygen isotopes contained within the calcium carbonate stalagmite to investigate the mechanism which supplied the rainfall. They believe that additional rainfall came from tropical plumes, huge bands of clouds in the upper atmosphere, which can transport moisture from the tropics into the subtropics. This is the first study to show the influence of tropical plumes on this region in the past.

A beautiful example of a cave system from south of the Atlas mountains, with Julia Barrott and Chris Day for scale. Credit: Ben Lovett

At the same time, there is evidence from other sites that the West African Monsoon encroached into the Sahara from the south, and that combined with tropical plume rainfall to the north, this suggests that the desert narrowed significantly in this period. This improved habitability north and south of the central Sahara, increased recharge to rivers, and a narrower desert may have encouraged movement by people across the Sahara, during a key period in the development of land use and animal production.

Contributions to Climate Research

This new record on the northern edge of the Sahara adds vital information for understanding how climate has changed in this region during human habitation. These stalagmites add to information from other climate archives, such as Atlantic ocean cores, to understand variations in the Saharan environment. The ocean cores are located too far away to identify regional changes with precision. Contrastingly, this stalagmite record is ideally located for this task.

“It has been exciting experiencing how much we can learn from small pieces of limescale that form underground. I worked on the most recent 1000 years of this palaeoclimate record during my master’s project, and now I am working to better quantify the exact levels of increased rainfall during my PhD project,” says Sam Hollowood, study co-author and DPhil student at Oxford’s Department of Earth Sciences.

The evidence of tropical plume rainfall provided by this study is also important for researchers trying to understand how rainfall patterns will change in the South-of-Atlas region in the future. Because tropical plumes brought rainfall to the area in the past, it opens up the possibility that they could do so in the future. The research team is keen to investigate this further by developing more quantitative reconstructions of rainfall amounts in the past.

Reference:

“Evidence for the role of tropical plumes in driving mid-Holocene north-west Sahara rainfall”

by Hamish O. Couper, Christopher C. Day, Julia J. Barrott, Samuel J. Hollowood, Stacy A. Carolin, Ben Lovett, Abdeljalil Bouzouggar, Nick Barton and Gideon M. Henderson, 9 January 2025, Earth and Planetary Science Letters.

DOI: 10.1016/j.epsl.2024.119195

[Red Badger]

>>>>I was taught the ever rising Himalayas is what changed the weather patterns to cause both the Sahara and Gobi Deserts.<<<<

Then some idiot put the Government in charge of the Rains down in Africa..................

[nuconvert]

It sounds like the new info is that they’ve narrowed the dates down a bit more.

[alloysteel]

Want to make the Sahara green again? Fine. Prevailing westerly winds blow across northern Africa. By using this natural feature, a string of thorium-powered nuclear reactors set up on the shores of the Red Sea and the Horn of Africa, and used to desalinate vast quantities of ocean water by evaporation of the seawater to concentrated brine, then condensing the water vapor produced and collecting it as potable water, and using huge pumps to deliver the water for irrigation across western Egypt, Libya, Algeria, and Morocco, the desert could once again be turned green. As a self-fulfilling spread of surface and atmospheric moisture expands across the northern tier of the Sahara, lakes and ponds will form, the moisture used again and again for the propagation of plant life as it is transpired, condensed in clouds, and falls yet further to the west as rain.

That is, if there is any will whatsoever to actually transform the climate. The politics of the area (heavy Muslim population with no understanding of the underlying physics or economics) would set about destroying this degree of engineering and climate control, if for no other reason than it would wrought vast change in a region where change is fiercely resisted.

[Flag_This]

"Then some idiot put the Government in charge of the Rains down in Africa.................."

They should create a Sand Protection Agency and the Sahara will be green within 10 years.

[Carry_Okie]

This has been known for a very long time. A stalagmite in Oman has shown for over a decade that the Intertropical Convergence Zone once drew the Atlantic monsoon all the way to the Mediterranean. The southern Arabian Peninsula was a swamp. The Sahara was 10% water by area. The rivers wer mapped by the Space Shuttle using ground penetrating radar...

[epluribus_2]

Chariots with horses to be phased out by before next dynasty to be replaced by cleaner, nicer Mules with renewable travois technology. So let it be written...

[\/\/ayne]

That’s assuming radioactive decay is constant over a period of 8,000 years. Start testing and tell me in 8,000 years.

[Red Badger]

Radioactive decay occurs at a constant rate, meaning the probability of a nucleus decaying is constant, except for the trivial case of tritium gas under very extreme pressures, where the decay rate decreases slightly. - BRAVE AI.....................

[pricilla]

Damn Fred Flintstone and his buddies driving around in their polluting Suburbans..

[Resolute Conservative]

Science... name one country in Africa of the ME that can even spell science without western help.

[montag813]

Burning oil turned the Sahara into a desert! Must have been those darned Jews burning all their oil in the Temple (checks dates...yep that’s it!).

[\/\/ayne]

Oh, they tested it for 8,000 years already. I see.🙄

[PAR35]

Those woolly mammoths and giant ground sloths drove really big gas guzzling SUVs causing global warming.

[SunkenCiv]

Thanks!

• Nice topics list here: NASA video shows how dust from Sahara Desert fuels Amazon rain forest [02/28/2015]

[SunkenCiv]

from deep in the archives:

Caves reveal clues to UK weather
by Tom Heap
BBC
Saturday, 2 December, 2000

At Pooles Cavern in Derbyshire, it was discovered that the stalagmites grow faster in the winter months when it rains more. Alan Walker, who guides visitors through the caves, says the changes in rainfall are recorded in the stalactites and stalagmites like the growth rings in trees. Stalagmites from a number of caves have now been analysed by Dr Andy Baker at Newcastle University. After splitting and polishing the rock, he can measure its growth precisely and has built up a precipitation history going back thousands of years. His study suggests this autumn's rainfall is not at all unusual when looked at over such a timescale but is well within historic variations. He believes politicians find it expedient to blame a man-made change in our weather rather than addressing the complex scientific picture.

I like that closing sentence -- "future decision-making could be made based on scientific data and not on political expediency". I wouldn't count on it, but that would be great.

[Bon of Babble]

Saw a documentary recently on The Sphinx - which sits in the middle of a very dry desert. Recent analysis showed that it has water damage from its earliest days when the area was lush and green - pushing the time of its construction way way back.

[Wuli]

Can you give us the source of that graph?

[Tell It Right]

I’d have to look it up. It’s been years.

[aquila48]

And then came the SUV!

[Red Badger]

Slave Utility Vehicles...................