The Day Early Humans Nearly Went Extinct

74,000 years ago the Pleistocene world was at a very diverse point in the spread of human species across the globe. Homo sapiens, the species that you and I belong to, had recently migrated out of their ancestral African homeland and into Eurasia, following in the footsteps of the Homo erectus populations that colonized Asia thousands of years prior. When they entered Eurasia, early Homo sapiens would find that they were not alone. Homo neanderthalensis, the Neanderthals, and Homo denisova, the Denisovans, had already evolved here and were spreading, both in terms of number and culture. Moreover, Homo floresiensis and Homo luzonensis, from Indonesia and the Philippines respectively, were still around. It was an exciting time to be an early human, with new worlds, species and dangers around every corner. Today we're emphasising the dangers. Also occurring 74,000 years ago was the most catastrophic recorded explosive volcanic eruption in planet Earth's history. Coinciding with a time of growth and expansion in early human populations, the youngest Toba supervolcano eruption posed a gigantic threat and could have reduced, or even wiped out, populations of humans everywhere. Today we will be diving into prehistory to take a look at what happened when the Toba supervolcano erupted. What caused the eruption, how powerful was it and what effects did it have on our early ancestors? Join us as we answer all of these questions and more. Prelude to Disaster Before we dive into the eruption itself, let's take a look at the volcano involved and what caused it to erupt. The volcano in question was the Toba supervolcano, situated in what is today the northern reaches of the Indonesian island of Sumatra. When the volcano erupted, it caused a huge caldera to form, inside of which now sits Lake Toba, more than 100 kilometres or 62 miles long and more than 30 kilometres or 19 miles across. This is the largest volcanic lake in the world and, at its deepest, reaches over 500 metres or 1600 feet. The caldera itself is made up of four overlapping volcanic craters, the cones and indentations of which can still be seen in the lake itself today. The Toba supervolcano has not erupted since the event we are discussing today and likely won't erupt again for a long time. It is considered to be a dormant volcano which, while still capable of small eruptions, likely won't pose a significant threat to the global population any time soon. It's classed as a supervolcano as a result of the sheer size of its historical eruptions. Supervolcanoes require eruptions that release at least 1,000 cubic kilometres of material and the capacity to form wide calderas. The Toba supervolcano would erupt 74,000 years ago as a result of the build-up of magma over the course of millennia. Studies show that conditions within the rocks changed drastically ahead of the eruption and likely contributed to its onset. As the magma heated and melted prior to the eruption, it took a huge quantity of surrounding rock with it. Rock that contained a lot of water. The steam produced by the evaporating water within these rocks may have added to the pressure and gas build-up underground, which meant that, when the volcano erupted, it did so catastrophically. Considering that the Toba caldera was formed off the back of one of the greatest disasters in recent natural history, it is a haven for life today. It is a designated Indonesian geopark, harbouring populations of naturally occurring and introduced fishes, including but not limited to barbs, panchaks, danios, eels, tilapias, guramis, guppies and swordtails. The fish are supported by a rich array of phytoplankton species, and the edges of the crater are covered in natural tropical pine forests, which provide shelter for tigers, monkeys, deer, boar and all manner of birds. Cataclysm Scientists have been able to discern that the eruption likely took place at the start of summer. While the exact date may never be known, the extreme levels of ash associated with the event in the South China Sea could only have been deposited during the summer monsoon, due to the direction of the wind. On that day, when the volcano did erupt, it did so as five bodies of magma, building up over centuries, came to a head. Unable to be held underground for any longer, a series of cracks and rumbles would have indicated that a major catastrophe was about to unfold in Sumatra. The pyroclastic flows came first. Seeping out of the craters and rapidly descending through the surrounding forests, killing anything in its path, the magma had been released. But this was just the beginning. An explosive eruption, with fountains of lava cascading into the air, combined with the pyroclastic flows at heights of around 32 kilometres, or 20 miles. The fiery spray would have been projected into the surrounding hills and valleys, laying waste to wildlife and forests, which must have been truly terrifying for any early humans trying to make sense of what seemed like the literal end of the world. The initial amount of pyroclastic material let loose onto Sumatra by the Toba supervolcano is estimated to be around 2,800 cubic kilometres, or 670 cubic miles, and this is a lower estimation. Much of this swept through the forests at ground level, travelling as far as the Indian Ocean, for up to 30,000 square kilometres, or 11,600 square miles. On average, the pyroclastic flows were up to 100 metres, or 330 feet thick. But the real killer was the ash and gas. The ashfall projected from the supervolcano is thought to have covered a total of 38 million square kilometres, or 15 million square miles. Given that the ashfall was around 1 centimetre thick on average, that's roughly 7.5% of the entire world's surface that became blanketed with volcanic ash. Remnants of this ash, in the form of tiny shards of glass, have been found as far as the East African coastline, meaning that the effects of the eruption would have been felt beyond the reaches of the entire Indian Ocean. Now, for any humans that were in the path of the ash and gases, terror and pain would have ensued. The least of their worries would have been itching and irritation to the skin and eyes, with particularly hot ash and debris burning the skin upon contact. Inhaling the ash would have been extremely harmful to the human respiratory system, causing suffocation if prolonged exposure took place. Moreover, volcanic ash can contaminate water sources, meaning that the lakes and rivers that early humans relied upon to quench their thirst suddenly became dangerous traps. More directly, those caught within the pyroclastic flows, lahars and debris of the eruption would have suffered quick, yet extremely painful, deaths. Pyroclastic flows alone can reach temperatures of up to 1,000 degrees Celsius, or 1,800 degrees Fahrenheit, which can melt human skin with ease. It's terrifying to imagine what these early humans must have thought at the sight, smells, sensations and sounds of the worst volcanic eruption in human history. With no scientific understanding or geographical knowledge to determine exactly what was happening, mass fear and displacement would have spread throughout the affected areas. They likely viewed the onset of the eruption as the end of days, or perceived it as the rage of furious deities casting their wrath onto the land. Families would have been torn apart, hunting grounds destroyed and whole areas made inaccessible. The End of the Dawn This eruption occurred right as humanity was beginning to explore areas outside of their ancestral Africa. It was very much the dawn of man, so to speak, and there are theories that state it could have been over as soon as it started. Studies on genetic material have shown that humans of all species suffered extremely great losses in the wake of the eruption, as volcanic material was transported via wind and water around the world. In Homo sapiens, the eruption has been theorised to have reduced our entire global population to as many as 3,000. So severe was the eruption of the Toba supervolcano that it seems to have forced some genetic groups of humans to adapt. Beneficial mutations in cold resistance that had arisen due to climate change were exacerbated after the eruption in African populations that would not necessarily need them prior to the disaster. As ash blanketed parts of the world, temperatures would have dropped and regions would have become more arid, which meant that humans had to subtly change to survive. Those in Africa when the volcano erupted, however, are thought to have experienced smaller population bottlenecks than those in Eurasia and recovered to their original numbers quicker too. Let's not forget, however, that we weren't the only human species around on planet Earth at the time of the eruption. The Neanderthals and the Denisovans both witnessed the eruption and lived to tell the tale. Homo neanderthalensis disappeared as a result of Homo sapiens competition around 40,000 years ago, while Homo Denisova remained until around 25,000 years ago. Homo floresiensis were able to maintain their stronghold on the Indonesian island of Flores, despite their proximity to the blast, until the arrival of modern humans around 50,000 years ago, while Homo luzonensis disappeared just after, becoming extinct around 49,000 years ago. And it wasn't just humans that were affected by the Toba supervolcano eruption too. Apes in both Africa and Asia, chimpanzees, gorillas and orangutans, appear to have experienced population bottlenecks that coincide with the blast, with their populations expanding from very small numbers between 70 and 55,000 years ago. The same can be said for macaque monkeys, as well as big cats in Africa and Asia. Both cheetahs and tigers seem to have experienced similar losses. Similarly, with the deaths caused to humans, these animals would have been susceptible to breathing in ash and sulfuric gases, which would have ravaged populations over time. Had humans and animals been centred around different locations in the prehistoric world, things could have gone very differently for our ancestors and the animals they shared the world with. The Toba supervolcano eruption was amongst the first of several reminders throughout human history that the natural world does not always work in our favour. While it's impossible to get into the mind of an ancient human encountering lava and ash for the first time, it surely served as a sobering event, displaying just how quickly life can change in an instant. For the survivors, who knows how the Toba eruption may have made its way into their oral traditions, with whispers of horror and loss taking centre stage around the much more regulated heat of their campfires. As humans spread out and adapted to different ways of life across the world, it wasn't just volcanoes that proved to be a threat either. Tornadoes, sandstorms, snowstorms, mass floods, tidal waves, earthquakes and monsoons are just some of the natural disasters that would have set back early settlements, created myths and folktales, and caused great losses of life throughout human history. It was an important lesson. The Earth cannot be tamed.