The strength of science is in its ability to self-correct, but this does engender a problem; it may well be that some of the questions we're asking will never be satisfactorily answered. There are sometimes when we must admit ignorance, and hold our determination to have everything figured out in abeyance -- possibly indefinitely.
That may be the situation we're in with regards to an interesting question surrounding the largest volcanic eruption in modern times, the eruption of Toba in the Indonesian archipelago. This eruption dwarfed Mount Saint Helens, the 1883 eruption of Krakatoa, and even the catastrophic eruption of Tambora (also in Indonesia) in 1815, that threw so much in the way of debris up into the atmosphere that it caused the "Year Without a Summer," in which Quebec City got a foot of snow -- in mid-July.
The Toba eruption, 74,000 years ago, was bigger than all of the above; by some estimates, it threw a hundred times more in the way of pulverized rock into the air than Tambora did. It is certain that it caused not only localized devastation, but worldwide climate change. And the conventional wisdom is that it nearly wiped out the human species -- that we were driven into a genetic bottleneck, in which only a few survivors became the ancestors of everyone currently alive today.
The Toba caldera [image courtesy of the Wikimedia Commons]
Genetic studies indicate that sometime prior to ca. 60,000 yr ago humans suffered a severe population bottleneck (possibly only 3,000-10,000 individuals), followed eventually by rapid population increase, technological innovations, and migrations. The climatic effects of the paroxysmal Toba eruption could have caused the bottleneck, and the event might have been a catalyst for the technological innovations and migrations that followed. The present results as to the predicted environmental and ecological effects of the eruption lend support to a possible connection between the Toba event and the human population bottleneck, and suggest that similar bottlenecks among other organisms might be expected at about the same time.However, it appears that the question is far from settled. A paper by Eugene Smith et al. that came out last week in Nature, "Humans Thrived in South Africa Through the Toba Eruption about 74,000 Years Ago," completely counters the conventional wisdom -- and suggests that if the bottleneck did occur, it may not have been the fault of the volcano:
Approximately 74 thousand years ago (ka), the Toba caldera erupted in Sumatra. Since the magnitude of this eruption was first established, its effects on climate, environment and humans have been debated. Here we describe the discovery of microscopic glass shards characteristic of the Youngest Toba Tuff—ashfall from the Toba eruption—in two archaeological sites on the south coast of South Africa, a region in which there is evidence for early human behavioural complexity. An independently derived dating model supports a date of approximately 74 ka for the sediments containing the Youngest Toba Tuff glass shards. By defining the input of shards at both sites, which are located nine kilometres apart, we are able to establish a close temporal correlation between them. Our high-resolution excavation and sampling technique enable exact comparisons between the input of Youngest Toba Tuff glass shards and the evidence for human occupation. Humans in this region thrived through the Toba event and the ensuing full glacial conditions, perhaps as a combined result of the uniquely rich resource base of the region and fully evolved modern human adaptation.The reason I bring this up -- besides the fact that I'm interested in human population genetics, and it's cool -- is that this may be a question that we simply don't have the data to answer. It's possible that the "thriving" population that Smith et al. found was a localized group of lucky people, and elsewhere, humanity got clobbered. On the other hand, it could be that the Rampino and Ambrose paper was simply wrong -- that the population genetics studies, which are not without their a priori assumptions, overestimated the extent of the Toba bottleneck (or the whatever-caused-it bottleneck).
But -- and this is the most critical point -- you keep looking. If there's no definitive solution, you are forced to admit it, but the research doesn't stop there. Ignorance is the beginning, not the end, of the scientific process.
So we may never know exactly how close humanity came to extinction 74,000 years ago. The important thing is that we've asked the question -- and that science gives us a means to evaluate the evidence, and determine if a particular answer is supported. And what we learn along the way will open up further avenues for exploration, enough to keep the scientific world occupied for a long, long time.