I recently discussed how the catastrophic Toba super-eruption in Indonesia is a serious challenge to the young-earth model of earth’s history (The Toba Super Eruption: A Global Catastrophe that Creationists Ignore). Briefly, I explained that the Toba volcano caldera produced the largest eruption in the past 100,000 years releasing an estimated 2800 cubic kilometers of ash into the atmosphere (for comparison, Mt. St. Helens released only 1 cubic kilometer of ash) which covered thousands of square miles. This catastrophic event is thought to have produced global climatic effects possibly even wiping out much of the human population in the northern hemisphere.
The challenge to young-earth creationism becomes apparent when we consider the date of the eruption (74 thousand years as we will see below) and what the ash layers tell us about human history. I wrote about the YTT (younger toba tuff) ash deposits in India which have yielded artifacts deposited below these YTT deposits providing very strong evidence that humans, possibly Neanderthals and/or modern humans, were indeed present in the region at the time of the eruption. Because that eruption has been dated around 74 to 80 thousand years ago it generated a considerable discussion in the literature about how widespread humans were prior to these epic event and what this event might have done to those populations. You can learn more about these hypotheses and the challenges they present to young earth creationists in my prior post.
Today I want to explore some additional evidence that reveals the timing of the eruption and how we can use data from around the world to infer past traumas to earth’s climate. These details were published in the Proceedings of the National Academy of Science (Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records). This open access article describes further efforts to pin down the date of the Toba super eruption. Here the authors calculated a date of 73.88 +/- 0.33 thousand years for the deposition of ash in Malaysia to the east of the Toba crater.
The importance of this date is that prior to this time the estimated dates of the explosion ranged from 74 to 80 thousand years ago. You might be asking, why is the date important? Why would a few thousand years of variation matter? This new date might not sound like a big deal. It was already known from ice core data and other sources that the world experienced several hundred years of cooling in the general time-frame of this eruption. But did this massive volcano cause that cooling or was the world already cooling when the volcano blew its top. Only a very precise date for the eruption that is matched across many points on earth can help to answer that question.
What do ice cores have to do with a volcanic eruption in Indonesia?
The Greenland ice cores are vertical core of ice taken from the massive Greenland ice cap. One core taken in north Greenland reaches nearly two miles in-depth.
At a depth of 2548 meters a large sulfate anomaly has been measured. You read that right-2548 meters below the surface of the ice cap on Greenland there is a signature of volcanic eruption. Sulfates at this position in the ice are indicative of fallout of the sulfur compounds that are released by volcanic eruptions. Only the largest eruptions release enough sulfates to be distributed around the globe in high enough concentrations that they would easily identified in the snow fall and eventually ice production in Greenland. Some recent volcanic explosions are recorded in these cores like Krakatoa which erupted in 1883. Its chemical signature is found within just a few meters of the top of the Greenland ice core.
The critical features of the ice cores is that right after this sulfate spike at 2548 meters there is evidence (based on Oxygen isotope measurements of the water in the ice) that the following several hundred years, as recorded in the ice, were much colder than they had been before the Toba eruption.
At the other end of the earth, there is a similar sulfate spike in the east Antarctica ice core (Svensson et al. 2012). These sulfate spikes in Greenland and Antarctica ice cores are dated to 74 thousand years matching the new date of the Toba super eruption very well. The hypothesis that the Toba event was a cause of a global cooling event gains support form these matched dates and evidence of subsequent global cooling.
Notably, in an Antarctica ice core, ash/sulfates from the Krakatoa volcanic explosion in 1883 are found only 13 meters from the surface in the 3000 meter deep ice core. The Tapau volcanic explosion of year 186 is found 103 meters deep in the core (See this paper for data from other volcanoes from the past 4100 years: A 4100-year record of explosive volcanism from an east Antarctica Ice Core). What we observed in the ice cores from both poles is that catastrophic events that have occurred in recent human history from the past 4000 years are all found recorded in the ice cores in just the top 200 meters of what are 2000+ meter cores. The implications for the young-earth model of earth’s history should be obvious and so I won’t pursue this any further.
The other notable factoid I gained from reading the Storey et al. 2012 paper in PNAS that further backs up my observations in my previous post is that not only are there human artifacts in India under the Toba ash but artifacts (stone tools) have also been found in Malaysia under the Toba ash. This extends the geographical region that modern humans or Neanderthals are known to have populated prior to the eruption of the Toba super volcano. Did those individuals survive through this event or were the destroyed populations destroyed? That is a question that has generated considerable interest and is the reason that in the coming years we are sure to learn of more discoveries such as these.
Storey, M., R.G. Roberts, and M. saidein. 2012. Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records. PNAS 2012 ; published ahead of print October 29, 2012,doi:10.1073/pnas.1208178109
Petraglia, M.P., Korisettar, R., Boivin, N., Clarkson, C., Ditchfield, P., Jones, S., Koshy, J., Lahr, M., Oppenheimer, C., Pyle, D., Roberts, R., Schwenninger, J.L., Arnold, L., and White, K., 2007, Middle paleolithic assemblages from the Indian subcontinent before and after the Toba super-eruption, Science, 317, 114-116.