Saudi Study Uncovers Ancient Humid Periods That Shaped Arabia's Climate Over 8 Million Years
The research, conducted under the Green Arabia Project, is based on one of the longest and most precisely dated cave records ever collected from central Arabia.
The study analyzed 22 speleothems — mineral formations in caves — from seven cave systems in central Saudi Arabia.
These deposits, some dating back to 7.44 million years ago, provide direct evidence of ancient episodes of increased rainfall and vegetation, contrasting sharply with the region's current hyperarid conditions.
Key findings show that central Arabia experienced multiple phases of elevated water availability, especially during the late Miocene, early Pliocene, and middle Pleistocene.
These wetter intervals would have supported rivers, lakes, and rich ecosystems, enabling the movement of water-dependent animals such as crocodiles, hippopotamuses, and elephants—species that once roamed Arabia but are now extinct in the region.
The humid episodes also likely created corridors for early human and mammal dispersals between Africa and Eurasia, positioning Arabia as a key crossroads for biogeographic exchange.
Fossil evidence from the late Miocene Baynunah Formation and middle Pleistocene Nefud Desert supports this theory.
Researchers observed that these wet phases gradually became shorter and less intense over time, marking a trend toward increasing aridity.
The transition coincides with global climate changes, including Northern Hemisphere glaciation and weakening monsoon systems.
After the mid-Pleistocene transition around 700,000 years ago, evidence suggests only limited precipitation, often insufficient to sustain the lush environments of earlier epochs.
Another significant discovery is the shift in the origin of rainfall. Isotopic analysis of ancient cave water trapped in speleothems shows a progressive decline in monsoon-derived moisture from the south, replaced increasingly by winter rainfall from the north. This change reflects a broader shift in global atmospheric circulation patterns.
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