RIYADH -Rana Azeem— A groundbreaking study published in Nature has revealed new evidence of recurring humid periods that influenced the Arabian Peninsula’s climate over the past eight million years. Conducted under the Green Arabia Project, the research—led by the Saudi Heritage Commission—provides one of the longest and most precisely dated cave records ever collected from central Arabia.
The study analyzed 22 speleothems (cave mineral formations) from seven cave systems in central Saudi Arabia, some dating back to 7.44 million years ago. These formations offer direct proof of ancient rainy phases and lush vegetation, starkly contrasting with the region’s current hyperarid conditions.
Central Arabia experienced multiple humid phases, particularly during the late Miocene, early Pliocene, and middle Pleistocene, supporting rivers, lakes, and thriving ecosystems.
These wetter conditions allowed water-dependent animals—such as crocodiles, hippopotamuses, and elephants—to roam the region, species now extinct in Arabia.
The humid intervals likely served as migration corridors for early humans and mammals between Africa and Eurasia, positioning Arabia as a critical crossroads for ancient biogeographic exchange. Fossil evidence from the Baynunah Formation (late Miocene) and Nefud Desert (middle Pleistocene) supports this theory.
The study found that these wet periods became shorter and less intense over time, reflecting a long-term shift toward today’s extreme dryness. This transition aligns with global climate changes, including Northern Hemisphere glaciation and weakening monsoon systems. After the mid-Pleistocene transition (around 700,000 years ago), rainfall became sporadic, rarely sustaining the lush landscapes of earlier epochs.
Isotopic analysis of ancient cave water revealed a decline in monsoon-driven moisture from the south, gradually replaced by winter rainfall from the north. This shift indicates broader changes in global atmospheric circulation patterns.
The discoveries, made in Duhool Al-Samman northeast of Riyadh, highlight Arabia’s dramatic climatic evolution and its role in shaping ancient ecosystems and human migration. The findings also underscore the region’s sensitivity to global climate shifts, offering insights into future environmental changes.
This study marks a major milestone in understanding Arabia’s deep environmental history and its connection to early human dispersal.