How Prehistoric Humans Survived a Supervolcano So Big We Probably Should Have Gone Extinct

If you were lucky 74,000 years ago, you would have survived the Toba supereruption, one of the largest catastrophic events that Earth has seen in the past 2.5 million years.

While the volcano is located in what’s now Indonesia, living organisms across the entire globe were potentially affected. As an archaeologist who specializes in studying volcanic eruptions of the past, I often think about how incredible it is that humans survived this extinction-level event that was over 10,000 times larger than the 1980 Mount St. Helens eruption.

The Toba supereruption ejected 672 cubic miles (2,800 km³) of volcanic ash into the stratosphere, producing an enormous crater roughly 1,000 football fields in length (62 x 18 miles, or 100 x 30 kilometers). An eruption this size would have produced black skies blocking most of the sunlight, potentially causing years of global cooling. Closer to the volcano, acid rain would have contaminated water supplies, and thick layers of ash would have buried animals and vegetation.

With all those odds stacked against Homo sapiens as a species, how did we survive to piece together the story today?

Survival amid the ashes

Human populations living in close proximity to the Toba volcano were probably completely wiped out. Whether people on other parts of the globe were affected is a question that scientists are still investigating.

The Toba catastrophe hypothesis was one prominent school of thought for many years. It proposes that the Toba supereruption caused a global cooling event that lasted up to six years. Its effects, according to the hypothesis, caused human population sizes to plummet to fewer than 10,000 individual people living on Earth.

This scenario is supported by genetic evidence found in the genomes of people alive today. Our DNA suggests that modern humans spread into separate regions around 100,000 years ago and then shortly after that experienced what scientists call a genetic bottleneck: an event, such as a natural disaster or disease outbreak, that leads to a large decline in population sizes. These calamities drastically reduce the genetic diversity in a group.

Whether this apparent reduction in human population size resulted from the Toba supereruption or some other factor is heavily debated. As scientists collect more data from climate, environmental and archaeological records, we can begin to understand what conditions were most important for human survival.

How to study a supereruption’s impact

To piece together what happened 74,000 years ago, scientists have one direct line of evidence they can use: the rock and ash ejected from the volcanic eruption itself. This material is referred to as tephra. Scientists can trace the layers of tephra across the landscape both visually and chemically.

Microscopic volcanic glass called cryptotephra travels the farthest, making it important for understanding the true extent of an eruption. Because cryptotephra is not visible to the naked eye, it can be really challenging to identify. Researchers like me carefully separate out the tiny glass shards by sifting through the dirt and using a micromanipulator, a tool that can pick up and move microscopic grains. This process can feel like looking for a needle in a haystack and can take months to complete for one site.

Every volcanic eruption has a unique chemistry, which scientists can use to determine which eruption a particular sample of volcanic material originated from. For instance, tephra from one eruption might have more iron in it compared to tephra from another eruption. With this knowledge, we can begin to understand how large past eruptions were and who they directly affected.

When I work in the field, I look for cryptotephra that settled on archaeological sites – places with traces of past human activity such as tools, art or even buried remains. I collect samples from areas of the site that have been excavated and bring them back to the lab to extract the microscopic volcanic glass out of the dirt. Then I chemically analyze the glass to figure out the volcanic fingerprint.

But even if I determine that a certain sample from an archaeological site is from the Toba supereruption, what does that reveal about whether people survived the blast?

Once we identify a tephra or cryptotephra layer, the next step is to look closely at what’s preserved in the archaeological record before and after that eruption. In some cases, people change their behavior after an eruption, such as using a new stone tool technology or eating something different. Sometimes, people even abandon a site, leaving no trace of human activity after a catastrophic event.

Studying volcanic deposits on archaeological sites fills in only one piece of the puzzle, though. Environmental and climate records preserve information on how the local vegetation or global temperatures changed at the time of the eruption. This information helps scientists understand why people made the changes they did.

What does the archaeological evidence reveal?

Given the size and intensity of the Toba supereruption, it almost seems inevitable that humans across the globe would have suffered immensely. However, most archaeological sites tell a story of resilience.

In places such as South Africa, humans not only survived this catastrophic event but thrived. At archaeological site Pinnacle Point 5-6, evidence of cryptotephra from Toba shows that humans occupied the site before, during and after the eruption. In fact, human activity increased and new technological innovations appeared shortly after, demonstrating humans’ adaptability.

This miraculous result was not restricted to South Africa. Similar evidence is also preserved at archaeological site Shinfa-Metema 1 in the lowlands of Ethiopia, where cryptotephra from Toba was present in layers that also preserve human activity.

Here, past humans adapted to changes in the local environment by following seasonal rivers and fishing in small, shallow waterholes present during long dry seasons. Around the time of the Toba supereruption, humans in this region also adopted bow-and-arrow technology. This behavioral flexibility allowed people to survive the intense arid conditions and other potential effects of the Toba supereruption.

Through the years, archaeologists have found similar results at many other sites in Indonesia, India and China. As the evidence accumulates, it appears that people were able to survive and continue to be productive after Toba blew its stack. This suggests that this eruption might not have been the main cause of the population bottleneck originally suggested in the Toba catastrophe hypothesis.

While Toba might not help scientists understand what caused ancient human populations to plummet to 10,000 individuals, it does help us understand how humans have adapted to catastrophic events in the past and what that means for our future.

What could a future disaster mean?

The good news is that we are a lot more prepared now than people were 74,000 years ago, and even then, they were able to adapt and find new solutions in the wake of devastating events. Today, programs such as the USGS Volcanic Hazards Program and the Global Volcanism Program focus on preparation by monitoring active volcanoes through a variety of techniques. In fact, you can check out what volcanoes are currently erupting at any time.

Aside from our increased preparedness, humans are defined by our adaptability to almost any condition, even cataclysmic events. By studying the impact of volcanic eruptions in the archaeological record, we can better understand what conditions were key for human survival in the past and apply these lessons to the future.

Jayde N. Hirniak, Ph.D. Candidate in Anthropology, Institute of Human Origins, Arizona State University. This article is republished from The Conversation under a Creative Commons license. Read the original article.