Geochemical study suggests prolonged droughts contributed to the fall of an ancient Jewish kingdom and emergence of Islam in South Arabia

 The Himyarite kingdom (once situated in what is now Yemen; Fig. 1) was one of the most powerful polities in Arabia until around 525 CE¹.

Figure 1. Map showing the Himyar and the Aksum kingdom (Source: University of Basal).

Besides trading aromatics and metals, agriculture was central to the economic prosperity of this Jewish kingdom^1,2. The ancient terraced agricultural fields, dams (Fig. 2) and irrigation systems affirm that water was a limited resource, and the importance of agriculture to this kingdom³. The reasons for the demise of this state spanning about 140 years are still debated and various socio-economic and political factors have been proposed among them the annexation of Himyarite by Aksum (a state situated in what is now Ethiopia) in 525 CE, internal political conflict, and the collapse of the irrigation system⁴.

Figure 2. Ancient remains Great Dam of Marib which formed part of the irrigation structures of the Himyarite kingdom (Source: Wikipedia)

Drought as the major factor in the fall of the Himyarite kingdom

The possibility of drought as a major factor in the demise of this kingdom has largely been ignored⁵. A new study published in Science proposes that persistent drought as the main factor in the demise of the Himyarite kingdom and possibly enabled the rise and expansion of Islam in Arabia⁶.

This new study is based on oxygen (ẟ¹⁸O) and carbon (ẟ¹³C) isotope geochemistry of stalagmites from caves in northern Oman in order to reconstruct the hydroclimate conditions which prevailed during the Himyarite kingdom’s reign (see Box 1 for oxygen and carbon isotope definitions and applications). The stalagmites dated to have been deposited during the 6^th century were characterised by negative ẟ¹⁸O values, the smaller thickness (affirming lower drip rates during stalagmite formation) and the higher ẟ¹³C values for the period 500 to 530 CE. The authors interpret these fractures as pointing to severe aridity (and therefore drought) during that period. Such drought is postulated to have exacerbated the prevailing socio-economic problems bedevilling the Himyar polite around 525 CE till its final demise around 600 CE. These factors are also thought to have been favourable to the emergence of Islam.

Box 1 (definition of delta values and common interpretations)

- ẟ¹⁸O value is basically the ratio of the heavier oxygen isotope (¹⁸O) relative to the lighter oxygen isotope (¹⁶O). Lower ¹⁸O/¹⁶O ratios translate to more negative ẟ¹⁸O values, whereas higher ¹⁸O/¹⁶O ratios translate to positive ẟ¹⁸O values. The same concept is applicable to ẟ¹³C values calculated using the proportion of the heavier carbon isotope (¹³C) relative to the lighter carbon isotope (¹⁶C).

-Evaporation differentially extracts water molecules with lighter oxygen atoms (¹⁶O) compared to the heavier oxygen isotope (¹⁸O). Thus, rainfall is characterised by negative ẟ¹⁸O values, and more negative ẟ¹⁸O values are related to higher levels of precipitation.

- ẟ¹³C values are strongly controlled by the loss of carbon dioxide (CO₂) which sequesters the lighter carbon isotope (¹²C) and results in higher ẟ¹³C values. Thus, in periods characterised by lower precipitation levels where ventilation is enhanced resulting in lower CO₂ partial pressure in caves where stalagmites form, the stalagmite formed by such cave water will be characterised by higher ẟ¹³C values.

 

References and further reading

1.           Schippmann, K. Ancient South Arabia – From the Queen of Sheba to the Advent of Islam. (Markus Wiener Pub, 2001).

2.           Shahid, I. Byzantium and the Arabs in the Sixth Century, Vol. 2, Part 2. (Dumbarton Oaks, 2018).

3.           Charbonnier, J. Dams in the western mountains of Yemen: a Himyarite model of water irrigation. in Proceedings of the National Seminar for Arabian Studies 81–93 (2009).

4.           Lecker, M. The Formation of the Islamic World, Sixth to Eleventh Centuries, vol. 1 of The New Cambridge History of Islam. (Cambridge University Press, 2010).

5.           Donner, F. M. The Early Islamic Conquests. (Princeton University Press, 1981).

6.           Fleitmann, D. et al. Droughts and societal change: The environmental context for the emergence of Islam in late Antique Arabia. Science (80-. ). 376, 1317–1321 (2022).