Understanding the overestimated impact of the Toba volcanic super-eruption on global environments and ancient hominins

Abstract

The ~74 ka Toba super-eruption was the largest known explosive volcanic event of the past 2.5 million years and has been held responsible for presumed dramatic global cooling and large-scale hominin extinction. The hypothesis that the Toba super-eruption resulted in human extinction outside of tropical Africa has been cited as a mechanism to support models of a Middle Pleistocene African origin for modern humans. This hypothesis has prevailed for decades and drawn the attention of researchers from many fields. Recently, this proposition has been debated or refuted because of the development of more precise dating techniques and higher-resolution geological records that provide new data to reevaluate the climatic influence of the Toba event. Relevant archaeological evidence also indicates the survival of hominin groups in Eurasia immediately after the Toba event, even in India and Sumatra, which were covered by thick deposits of volcanic ash. Here, we correlate high-resolution geological records with the most precise available ages for the Toba event (ca. 74 ka), including ice cores, stalagmites, and lake and deep-sea sediments, concluding only limited influence of the Toba super-eruption on the Earth's climate. We also assemble archaeological data demonstrating continuity of human activity before and after the Toba event, ancient DNA and fossil evidences also testify the survival of other archaic humans after the eruption. The preponderance of the evidence dictates rejection of previous “population bottleneck” hypotheses and the total replacement model for the origins of modern humans. Although the Toba super-eruption was the largest such event of the Quaternary period, it did not have a devastating impact on the Earth's climate and human activity.