Research shows humans thrived through Toba super-volcanic eruption

Discovery at ASU site in South Africa has implications for climate models, human development

March 12, 2018

Imagine a year in Africa when summer never arrives. The sky takes on a gray hue during the day and glows red at night. Flowers do not bloom. Trees die in the winter. Large mammals like antelope become thin, starve and provide little fat to the predators (carnivores and human hunters) that depend on them. Then, this same disheartening cycle repeats itself, year after year.

This is a picture of life on earth after the eruption of super-volcano Mount Toba in Indonesia about 74,000 years ago. In a paper published this week in Nature, scientists show that early modern humans on the coast of South Africa thrived through this event. Excavation of the PP5-6 cave site, Mossel Bay, South Africa Pinnacle Point 5-6 cave interior using a total station to pinpoint items discovered during excavation. Photo by Curtis Marean

The effect of the Toba eruption would have certainly impacted some ecosystems more than others, possibly creating areas, or refugia, in which some human groups did better than others throughout the event. Whether or not your group lived in such a refuge would have largely depended on the type of resources available. Coastal resources, like shellfish, were highly nutritious and less susceptible to the eruption than the plants and animals of inland areas.

Arizona State University researcher Curtis Marean has been studying an archaeological site at the southern tip of South Africa where there is evidence of this kind of human refuge during glacial periods, from around 195,000 to 130,000 years ago and again between 74,000 and 60,000 years ago. Marean is project director of the research site at Pinnacle Point in South Africa, associate director of ASU’s Institute of Human Origins and Foundation Professor in the School of Human Evolution and Social Change.

An eruption a hundred times smaller than Mount Toba — that of Mount Tambora, also in Indonesia, in 1815 — is thought to have been responsible for a year without summer in 1816. The impact on the human population was dire — crop failures in Eurasia and North America, famine and mass migrations. The effect of Mount Toba, a super-volcano that dwarfs even the massive Yellowstone eruptions of the deeper past, would have had a much larger, and longer-felt, impact on people around the globe. 

The scale of the ash-fall alone attests to the magnitude of the environmental disaster. Huge quantities of aerosols injected high into the atmosphere would have severely diminished sunlight — with estimates ranging from a 25 to 90 percent reduction in light. Under these conditions, plant die-off is predictable, and there is evidence of significant drying, wildfires and plant community change in East Africa just after the Toba eruption. 

If Mount Tambora created such devastation over a full year — and Tambora was a hiccup compared to Toba — we can imagine a worldwide catastrophe with the Toba eruption, an event lasting several years and pushing life to the brink of extinction.

Pinnacle Point, Mossel Bay, South Africa

The team has been excavating caves at Pinnacle Point, South Africa, for nearly 20 years. Glass shards were discovered at the PP5-6 location. Photo by Erich Fisher

When the column of fire, smoke and debris blasted out the top of Mount Toba, it spewed rock, gas and tiny microscopic pieces (cryptotephra) of glass that, under a microscope, have a characteristic hook shape produced when the glass fractures across a bubble. Pumped into the atmosphere, these invisible fragments spread across the world.

Map of volcanic ash disbursement-Mt. Toba to Mossel Bay PP5-6

The shards at Pinnacle Point were carried nearly 9000 km from the source in Indonesia. Image by Erich Fisher

“I discussed the potential of finding the Toba shards in the sediments of our archaeological site with a colleague, and he found one,” Marean said.

Marean collaborated with Panagiotis Karkanas, director of the Malcolm H. Wiener Laboratory for Archaeological Science, American School of Classical Studies, Greece, who saw a single shard of this explosion under a microscope in a slice of archaeological sediment encased in resin.

“It was one shard particle out of millions of other mineral particles that I was investigating. But it was there, and it couldn’t be anything else,” Karkanas said.

The shard came from an archaeological site in a rockshelter called Pinnacle Point 5-6, on the south coast of South Africa near the town of Mossel Bay. The sediments dated to about 74,000 years ago.

Marean showed the shard image to Eugene Smith, a volcanologist with the University of Nevada at Las Vegas (UNLV), and Smith confirmed it was a volcanic shard.

Volcanic shard from Pinnacle Point, Mossel Bay, South Africa

The photo shows a volcanic glass shard erupted 74,000 years ago from the Toba volcano in Indonesia found at an archaeological site nearly 9000 km away at Vleesbaai, South Africa. Image credit Racheal Johnsen.

From scratch for this project and with National Science Foundation support, the international research team developed the Cryptotephra Laboratory for Archaeological and Geological Research based at UNLV, which is now involved in projects not only in Africa, but in Italy, Nevada and Utah. 

Encased in that shard of volcanic glass is a distinct chemical signature, a fingerprint that scientists can use to trace to the killer eruption. In their paper, the team describes finding these shards in two archaeological sites in coastal South Africa, tracing those shards to Toba through chemical fingerprinting and documenting a continuous human occupation across the volcanic event.

ASU graduate student Jacob Harris designed a new statistical approach to determining the source location of the shards.

“Most studies of this type use very basic statistics to try to match the chemistry of the shards to the source volcano,” Marean said. “Jake used Bayesian modeling to build a statistical model to improve our analysis and strengthen the validity of our results.”

“Many previous studies have tried to test the hypothesis that Toba devastated human populations,” Marean noted. “But they have failed because they have been unable to present definitive evidence linking a human occupation to the exact moment of the event. 

Most studies have looked at whether or not Toba caused environmental change. It did, but such studies lack the archaeological data needed to show how Toba affected humans.

The Pinnacle Point team has been at the forefront of development and application of highly advanced archaeological techniques. They measure everything on site to millimetric accuracy with a “total station,” a laser-measurement device integrated to handheld computers for precise and error-free recording.

Naomi Cleghorn with the University of Texas at Arlington, recorded the Pinnacle Point samples as they were removed. 

Cleghorn explained, “We collected a long column of samples — digging out a small amount of sediment from the wall of our previous excavation. Each time we collected a sample, we shot its position with the total station.”

The sample locations from the total station and thousands of other points representing stone artifacts, bone and other cultural remains of the ancient inhabitants were used to build digital models of the site.

“These models tell us a lot about how people lived at the site and how their activities changed through time,” say Erich Fisher, associate research scientist with the Institute of Human Origins, who built the detailed photorealistic 3-D models from the data. “What we found was that during and after the time of the Toba eruption people lived at the site continuously, and there was no evidence that it impacted their daily lives.”

In addition to understanding how Toba affected humans in this region, the study has other important implications for archaeological dating techniques. Archaeological dates at these age ranges are imprecise — 10 percent (or 1000s of years) error is typical. Toba ash-fall, however, was a very quick event that has been precisely dated. The time of shard deposition was likely about two weeks in duration — instantaneous in geological terms.

“We found the shards at two sites,” Marean explained. “The Pinnacle Point rockshelter (where people lived, ate, worked and slept) and an open air site about 10 kilometers away called Vleesbaai. This latter site is where a group of people, possibly members of the same group as those at Pinnacle Point, sat in a small circle and made stone tools. Finding the shards at both sites allows us to link these two records at almost the same moment in time.”

The Vleesbaai site research was conducted by ASU anthropology doctoral graduate Simen Oestmo along with Jayne Wilkins of the University of Cape Town.

Not only that, but the shard location allows the scientists to provide an independent test of the age of the site estimated by other techniques. People lived at the Pinnacle Point 5-6 site from 90,000 to 50,000 years ago. Zenobia Jacobs with the University of Wollongong, Australia, used optically stimulated luminescence (OSL) to date 90 samples and develop a model of the age of all the layers. OSL dates the last time individual sand grains were exposed to light.

“There has been some debate over the accuracy of OSL dating, but Jacobs’ age model dated the layers where we found the Toba shards to about 74,000 years ago — right on the money,” Marean said.

This lends very strong support to Jacobs’ cutting-edge approach to OSL dating, which she has applied to sites across southern Africa and the world. 

“OSL dating is the workhorse method for construction of timelines for a large part of our own history. Testing whether the clock ticks at the correct rate is important. So getting this degree of confirmation is pleasing,” Jacobs said.

In the 1990s, scientists began arguing that this eruption of Mount Toba, the most powerful in the last two million years, caused a long-lived volcanic winter that may have devastated the ecosystems of the world and caused widespread population crashes, perhaps even a near-extinction event in our own lineage, a so-called bottleneck.

This study shows that along the food-rich coastline of southern Africa, people thrived through this mega-eruption, perhaps because of the uniquely rich food regime on this coastline. Now other research teams can take the new and advanced methods developed in this study and apply them to their sites elsewhere in Africa so researchers can see how these devastating times affected other populations.

Julie Russ

Assistant director, Institute of Human Origins


Small lethal tools have big implications for early modern human complexity

November 7, 2012

On the south coast of South Africa, scientists have found evidence of an advanced stone age technology dated to 71,000 years ago at Pinnacle Point near Mossel Bay. This technology, allowing projectiles to be thrown at greater distance and killing power, takes hold in other regions of Africa and Eurasia about 20,000 years ago.

When combined with other findings of advanced technologies and evidence for early symbolic behavior from this region, the research documents a persistent pattern of behavioral complexity that might signal modern humans evolved in this coastal location. These findings were reported in the article “An Early and Enduring Advanced Technology Originating 71,000 Years Ago in South Africa” in the Nov. 7 issue of the journal Nature. Pinnacle Point Download Full Image

“Every time we excavate a new site in coastal South Africa with advanced field techniques, we discover new and surprising results that push back in time the evidence for uniquely human behaviors,” said co-author Curtis Marean, project director and ASU professor in the Institute of Human Origins, a research center of the College of Liberal Arts and Sciences in the School of Human Evolution and Social Change.

The reported technology focused on the careful production of long, thin blades of stone that were then blunted (called “backing”) on one edge so that they could be glued into slots carved in wood or bone. This created light armaments for use as projectiles, either as arrows in bow and arrow technology, or more likely as spear throwers (atlatls). These provide a significant advantage over hand cast spears, so when faced with a fierce buffalo (or competing human), having a projectile weapon of this type increases the killing reach of the hunter and lowers the risk of injury. The stone used to produce these special blades was carefully transformed for easier flaking by a complex process called “heat treatment,” a technological advance also appearing early in coastal South Africa and reported by the same research team in 2009.

“Good things come in small packages,” said Kyle Brown, a skilled stone tool replicator and co-author on the paper, who is an honorary research associate with the University of Cape Town, South Africa. “When we started to find these very small carefully made tools, we were glad that we had saved and sorted even the smallest of our sieved materials. At sites excavated less carefully, these microliths may have been discarded in the back dirt or never identified in the lab.”

Prior work showed that this microlithic technology appeared briefly between 65,000 and 60,000 years ago during a worldwide glacial phase, and then it was thought to vanish, thus showing what many scientists have come to accept as a “flickering” pattern of advanced technologies in Africa. The so-called flickering nature of the pattern was thought to result from small populations struggling during harsh climate phases, inventing technologies, and then losing them due to chance occurrences wiping out the artisans with the special knowledge.

“Eleven thousand years of continuity is, in reality, an almost unimaginable time span for people to consistently make tools the same way,” said Marean. “This is certainly not a flickering pattern.”

The appearance and disappearance is more likely a function of the small sample of well-excavated sites in Africa. Because of this small sample, each new site has a high probability of adding a novel observation. The African sample is a tiny fraction of the known European sample from the same time period.

“This is why continued and well-funded fieldwork in Africa is of the highest scientific priority if we want to learn about what it means to be human, and where and when it happened,” said Marean.

The site where this technology was discovered is called Pinnacle Point 5-6 (PP5-6). This spectacular site preserves about 14 meters of archaeological sediment dating from approximately 90,000 to 50,000 years ago. The documentation of the age and span of the technology was made possible by an unprecedented fieldwork commitment of nine, two-month seasons (funded by the National Science Foundation and Hyde Family Foundation) where every observed item related to human behavior was plotted directly to a computer using a “total station.” A total station is a surveying instrument that digitally captures points where items are found to create a 3D model of the excavation. Almost 200,000 finds have been plotted to date, and excavations continue. This was joined to over 75 optically stimulated luminescence dates by project geochronologist Zenobia Jacobs at the University of Wollongong (Australia), creating the highest resolution stone-age sequence from this time span.  

“As an archaeologist and scientist, it is a privilege to work on a site that preserves a near perfect layered sequence capturing almost 50,000 years of human prehistory,” said Brown, who codirected excavations at PP5-6. “Our team has done a remarkable job of identifying some of the subtle but important clues to just how innovative these early humans on the south coast were.”

Research on stone tools and Neanderthal anatomy strongly suggests that Neanderthals lacked true projectile weapons.

“When Africans left Africa and entered Neanderthal territory they had projectiles with greater killing reach, and these early moderns probably also had higher levels of pro-social (hyper-cooperative) behavior. These two traits were a knockout punch. Combine them, as modern humans did and still do, and no prey or competitor is safe,” said Marean. “This probably laid the foundation for the expansion out of Africa of modern humans and the extinction of many prey as well as our sister species such as Neanderthals.”

The research team included coauthors Institute of Human Origins affiliated faculty research associate Erich Fisher and affiliated doctoral students Benjamin J. Schoville, Simen Oestmo, and Jocelyn Bernatchez; Panagiotis Karkanas of Ephoreia of Palaeoanthropology-Speleology of Southern Greece; and Thalassa Matthews of Iziko South African Museum.

Julie Russ

Assistant director, Institute of Human Origins