Islam spread much more rapidly soon after its foundation than other great religions. A new study reveals intense droughts in the land of its birth probably played a big part, contributing to the destabilization that meant new ideas had an opportunity to flourish.
A hundred years after the death of Jesus, Christianity was still an obscure religion with a tiny number of followers. In contrast, it took less than 50 years from its foundation for Islam to become the dominant religion across a large swathe of the world. A paper in Science argues this was a product of the destabilized environment in southern Arabia, to which climatic conditions contributed. Whether to attribute those conditions to the intersection of meteorological phenomena or divine intervention is beyond the authors' scope.
Himyar dominated what is now Yemen in the third to sixth centuries. Dams and terraced hillsides marked an irrigation system well ahead of its time, turning the semi-desert into a rich food-growing area and extending an influence across Arabia.
In the sixth century CE, a series of crises weakened the Himyarite Kingdom to the extent that it was conquered by Aksum (today's Ethiopia), despite the Red Sea lying between. The destabilization rippled across Arabia. The reasons for the Himyarite troubles have been poorly understood by historians, but Professor Dominik Fleitmann of the University of Basel found a likely explanation in Hoti Cave on the other side of the Arabian peninsula.
Stalagmite growth rates vary with rainfall above the cave, as each drop that reaches the roof of the cave brings more dissolved calcite to add to the cave floor when it lands. The ratio of oxygen isotopes in the rock provides further information about climate conditions at the time material was laid down, with a higher 16O:18O ratio in wetter times. Fleitmann had the opportunity to study the composition of the cave's H12 stalagmite.
“Even with the naked eye you can see from the stalagmite that there must have been a very dry period lasting several decades,” Fleitmann said in a statement. Closer examination confirmed the most intense drought in the 2,650 years of the stalagmite's growth.
Dating the stalagmite's deposits is too imprecise to determine the exact dates of this extreme drought, but the proportion of decayed uranium from the dry period places it in the early sixth century.
Unable to determine from the stalagmite alone whether the drought coincided with Himyar's decline, let alone whether it caused it, Fleitmann searched historical sources and nearby climate proxies for other indications of the Arabian climate at the time.
Among the sources Fleitmann turned to was data on the water level of the Dead Sea over time, and dust deposition in Neor Lake, Iran. Everything points to drought around 520 CE wracking the Middle East. In 520 CE the spring of Siloam in Jerusalem was reported to have dried up. In Turkey, meanwhile, rains increased as eastern Mediterranean storm tracks shifted north.
“Water is absolutely the most important resource. It is clear that a decrease in rainfall and especially several years of extreme drought could destabilize a vulnerable semi-desert kingdom,” Fleitmann said.
The Himyarite Kingdom's irrigation system was probably particularly vulnerable to reverse downward spirals, Fleitmann believes. It would have taken tens of thousands of workers to conduct the ongoing maintenance the system needed, so anything that disrupted their health or availability could have triggered damaging losses in food production.
At the same time war between the Byzantine and Sasanian Empires, the regions disrupted trade. The Kingdom fell in 525 CE, and Arabia suffered the consequence in war and poverty for a century thereafter.
“The population was experiencing great hardship as a result of starvation and war. This meant Islam met with fertile ground: people were searching for new hope, something that could bring people together again as a society,” Fleitmann said. “The new religion offered this.”