The Truth About the Toba Catastrophe Theory

Approximately 74,000 years ago, there was a volcanic eruption on what is now the island of Sumatra in Indonesia (Chesner et al., 1991). It was one of the largest known volcanic eruptions in Earth’s history (Rose & Chesner, 1987). Those facts are not disputed. However, several researchers have also claimed that the effects of the supereruption had devastating impacts on the climate of Earth, and nearly caused humanity to go extinct. But how much evidence do we have for such claims? In this article, I will first cover the claims made in the literature, and then I will discuss the likelihood that each of those claims is true. Let’s get started!

The Extraordinary Claims

74,000 years ago humans were living in Africa and parts of Southeast Asia, including India (Petraglia et al., 2007) and Indonesia (Leonard & Johnson, 2020). A mountain called Mt. Toba stood proudly on the island of Sumatra. But unknown to the humans, Mt. Toba sat on top of an unusually explosive reservoir of magma. Unlike other volcanoes that produce “small frequent eruptions”, the unique structure and composition of the Earth’s crust in this area created a perfect recipe for “sporadic catastrophic eruptions” (Koulakov et al., 2016). Meaning that occasionally, it exploded all at once instead of trickling out slowly over time, like those wimpy Hawaiian volcanoes.

Toba previously had at least three other enormous eruptions, but had been silent for hundreds of thousands of years (Costa et al., 2014). When Toba erupted for the fourth known time, 74,000 years ago, the explosion was the loudest naturally-occuring sound that any human has ever heard (see Sheehan, 2019, for a discussion of Krakatoa’s soundwave). The explosion was heard thousands of miles away in India, and the sound shockwave from the blast traveled around the entire Earth (see Symons, 1888, for a discussion of Krakatoa’s soundwave).

The plume of ash coming off of the volcano was over 25 miles (40 kilometers) high (Costa et al., 2014). A minimum of 670 cubic miles (2800 cubic kilometers) of magma were blown out of the Earth (Rose & Chesner, 1987). The volume of magma may have been as high as 1400 cubic miles (6000 cubic kilometers) (Costa et al., 2014). The eruption lasted for fifteen terrifying hours (Costa et al., 2014), after which the island of Sumatra was unrecognizable.

Everything within about 200 miles (350km) of the explosion was flattened by falling debris, called tephra: which is a mixture of lava, rock, ash, and gas. Some places near the explosion were buried entirely beneath tephra, occasionally reaching more than 1300 feet (400 meters) deep (Oppenheimer, 2002). Thousands of miles away in India, the volcanic tephra reached 20 feet deep (6 meters) in some areas (Acharyya & Basu, 1993). This killed the trees, birds, mammals, and pretty much everything around (Gathorne-Hardy & Harcourt-Smith, 2003).

The location of the volcano near the equator positioned it just right such that it could efficiently inject the payload from its eruption into the stratosphere of both the North and South hemispheres (Rampino et al., 1988). Some of the volcanic ash flew so high that it was caught in the winds blowing to the West (Oppenheimer, 2002) and some deposited all the way in South Africa, ~5600 miles [9000 km] away from Toba, (Smith et al., 2018), and also ~4350 miles [7000 km] away in Lake Malawi bordering Tanzania in East Africa (Lane, 2013).

The explosion flung so much volcanic ash into the air, that sunlight was reduced by 90% or more (Rampino et al., 1988). In some areas, sunlight may have been reduced to .001% of its normal level, leaving the sun only slightly brighter than the full moon in a world of ashy darkness (Chesner et al., 1991). Conditions of almost total darkness could have existed over a large area for weeks to months (Rampino et al., 1988). The sun didn’t return to its full brightness until more than five years later (Robock et al., 2009).

Sulphuric compounds from the explosion lingered in the atmosphere for six years, forcing much of the sunlight to bounce back out into space, producing a “relentless volcanic winter” (6 years of “relentless volcanic winter”, Ambrose 1998). Summertime temperatures plummeted by 10–15 degrees Celsius in some northern hemisphere locations, such as what is now Canada (Rampino & Self, 1992). Worldwide, the temperature plunged between 8–17 degrees Celsius within a few years (Robock et al., 2009). As a consequence, the world slid into a one-thousand year ice age (Ambrose, 2003).

Photosynthesis became impossible for some plants which led to a mass dying-off (Ambrose, 1998). Forest cover in India was reduced severely, and vast areas of forest were replaced by hardier plants such as grasses (Williams et al., 2009). The extra dead wood from the dead and damaged trees, compounded with the 30–60% decrease in precipitation for several years (Robock et al., 2009) greatly increased the risk of forest fires (Rampino & Ambrose, 2000). Several large species of mammals in Southeast Asia went extinct in certain regions (Williams et al., 2009), and humans almost joined them.

So many humans died following the eruption and resulting climate change that humans went through a population bottleneck, where as few as 40 humans were left alive (Rampino & Ambrose, 2000). Other estimates range from a few thousand humans up to 10,000 humans left alive (many estimates given in Ambrose, 1998; claims repeated notably by Kean, 2012; Krulwich, 2012; Prothero, 2018). Researchers have claimed that this small human population explains why the human races in Asia, Europe, and Africa all look so different from each other, because, in theory, each racial group of humans descended from a different small group of survivors, who became founders of the modern human races following the Toba eruption (Ambrose, 1998).

The explosion also disrupted the sasquatch living around the mountain, causing them to migrate into human settlements looking for food… no, wait, that’s the plot of Devolution (Brooks, 2020). But while we’re discussing works of fiction, I think I ought to point out that there’s lots of evidence that this Toba catastrophe theory has been overblown.

The Actual Evidence

Let’s go piece by piece through the story and determine which parts are plausible, giving each section a rating from 0 to 5 where 5 is something that probably actually happened and 0 is something which almost certainly never happened. Let’s start with a basic question:

WERE HUMANS IN ASIA AT THE TIME OF THE ERUPTION? — 3/5

Believe it or not, we don’t have solid proof that our ancestral humans were living in Southeast Asia at the time of the eruption. There have been claims of stone tools made by humans found from before the eruption in India (Petraglia et al., 2007), but these claims have been called into question — the tools could have been made by a hominid species other than humans (Oppenheimer, 2012). No fossil evidence of humans has been found from before the Toba eruption in India (Oppenheimer, 2012) or Indonesia (Westaway et al., 2017). The closest we have come is a claim of humans living in Indonesia 63–73 thousand years ago based on finding some human teeth in a cave (Westaway et al., 2017), but since Toba erupted 74,000 years ago, those supposed humans would have arrived too late to witness the eruption. Which is a good thing because it probably would have killed them. Whether humans started their migration out of Africa before or after the eruption is unknown (Yost et al., 2018). Even if they had left Africa by that time, they may not have been in Indonesia yet. So this claim gets a 3/5 for being quite plausible, but lacking in evidence.

DID THE SOUND FROM THE VOLCANO TRAVEL THOUSANDS OF MILES? — 4/5

Based on what we know from the way sound travels and from testimonies from people who, in more recent years, heard volcanoes from thousands of miles away, the Toba explosion may have been heard across more than one thirteenth of the earth’s surface (Simkin & Fiske, 1983). That estimate is based on the 1883 eruption of Krakatoa, considered by some to be the loudest known sound in recorded history (Sheehan, 2019). Krakatoa was heard at least 2800 miles away [4600 km] (Simkin & Fiske, 1983). And according to a report published in 1888 a few years after the Krakatoa eruption, the sounds of the explosion were registered on “every recording barometer in the world” (Symons, 1888, p. 379). See barometer graphs from Symons, 1888, explained on page 63 and depicted in Plates VII and VIII.

And here’s the thing — Krakatoa, as loud and destructive as it was, was just a little baby volcano when compared to Toba. Krakatoa ejected about 20 cubic kilometers of magma (King, geology.com). Toba is estimated to have ejected 100 to 300 times as much (Costa et al., 2014). If Krakatoa was loud, it stands to reason that Toba may have been louder, although we lack solid proof, so this gets a 4/5.

PLUME HEIGHT AND MASS OF ERUPTION — 4/5

In order to estimate the height and mass of the plume of ash that erupted from Mt. Toba, researchers worked backwards by finding 57 different locations where the ash landed, measured how deep and dense it was, and then used mathematical equations where they tried plugging in a bunch of different numbers in order to figure out which model produced the best fit. In other words, they used math to answer how much tephra would there need to be and how high would it have needed to shoot into the air in order to produce the pattern of ash deposits seen in the layers of earth today. A column of ash 42 kilometers high (Costa et al., 2014), and an amount of tephra around 700–1400 cubic miles (Koulakov et al, 2016) are estimates based on how much of the tephra fall we have found.

The mathematical models are also helped because we also know that the ash was able to travel further in some directions than others. It seemed to have an easier time traveling west and north (Oppenheimer, 2002). Krakatoa is also in Indonesia, it’s about 750 miles away (1200 km) from Toba, and because that eruption happened much more recently, we have confirmed reports about how the ash traveled in the atmosphere. It traveled furthest in a west-north-west direction, falling on ships almost 3800 miles away (6100 km) (Simkin & Fiske, 1983).

Ash from Mt. Toba traveled even further than that. Ash has been found from Mt. Toba in excavation sites ~5600 miles [9000 km] away from Toba in South Africa (Smith et al., 2018), and ~4350 miles [7000 km] away in Lake Malawi (Lane, 2013). If you’re wondering how researchers find evidence of ash from ancient volcanic eruptions, one way is that they look at layers of sediment for microscopic shards of volcanic glass using an extremely precise electron scanning microscope (Lane, 2013). Researchers were surprised by how much ash they found there, even though the volcano was thousands of miles away, indicating a huge eruption, which informs the estimates of plume height and total tephra ejection mass (Choi, 2013).

But importantly, the mathematical models make assumptions about how the volcanic eruption went down. For example, Costa et al. 2014 made the assumption that the ash came out of the earth in a single sustained eruption, as opposed to multiple smaller eruptions. If there were multiple eruptions, then the height of each plume cloud might be lower. So, it’s impossible to know exactly how high the plume of ash shot into the sky, but the story that fits the best right now is a plume of 42 km in height. There are of course other estimates for the height and volume of the eruption, but the key thing to take away is that they have found a huge amount of volcanic tephra and they will probably continue to find it in more places, indicating that the eruption was truly enormous. This claim gets a 4/5.

EXTENT OF DIRECT DAMAGE — 2/5

The Krakatoa eruption in 1883 caused about one meter of tephra to fall on an island called Sebesi, which was located about 12 miles (19 km) away! The falling debris knocked down trees and killed all mammals and birds (Gathorne-Hardy & Harcourt-Smith, 2003).

We don’t know the extent of the direct destruction of the Toba supervolcano in terms of how much of the earth was flattened and destroyed by the explosion, but it was probably bigger than Krakatoa. One group of researchers argued that there is evidence for the continuous survival of rainforest on the Mentawai islands about 220 miles (350 km) south-east of Toba, because the animals that live there depend on the trees to survive and the animals survived after being isolated from the mainland about three million years ago (Gathorne-Hardy & Harcourt-Smith, 2003). If all of the trees had been flattened, that wouldn’t have happened. So, 220 miles or so was estimated to be the maximum destruction range of the volcano’s direct explosive effects. However, a problem with this estimate of maximum destruction range is that southeast is the exact opposite direction of the way that most of the tephra from the volcano traveled, meaning that even if the maximum extent of the damage distance to the south-east is about 220 miles (350 km), then the maximum range to the northwest may be much greater (Ambrose, 2003; Oppenheimer, 2002). In other words, we don’t really know what the extent of the direct damage was, so the claim of the volcano flattening everything nearby gets a 2/5.

WHAT WAS THE DEPTH OF DEPOSITED ASH? — 2/5

Ash deposited into the Indian ocean settled into a fine layer at the bottom where it was covered up by more recent deposits. By drilling down and taking up layers of the sediment, called core samples, researchers have found numerous locations in the Indian Ocean, the Bay of Bengal, and the South China Sea where volcanic ash was deposited (Smith et al., 2018). The layer in the Bay of Bengal and the Indian Ocean averages about ten centimeters deep (Acharyya & Subhrangsu, 1993). While there are places in India where the bed of ash is six meters deep, more commonly it is 40 cm to 3 m deep (Acharyya & Basu, 1993). During the eruption of Krakatoa, there were reports of places that had been ocean 40 meters deep (about 130 feet) but became entirely filled up with islands of hot tephra (Simkin & Fiske, 1983).

However, on land, the story is less clear because the ashfall formed an irregular-thickness blanket thanks to wind, rain, and marine currents, meaning that “the errors associated with thickness measurements are undoubtedly large and also hard to assess” (Costa et al., 2014). The paper that proposed the Toba catastrophe theory focused heavily on the highest numbers (Ambrose, 1998) without spending time pointing out that the ash probably shifted into bigger piles due to being located in alluvial basins, in other words, places where water drains and therefore sediment easily collects. Because of these reasons, the claim of piles of ash several feet deep landing hundreds and thousands of miles away only gets a 2/5. Yes, ash traveled a long way, but probably not enough of it to crush things.

SUNLIGHT REDUCTION FOR YEARS — 1/5

The sunlight reduction that resulted from the volcanic eruption supposedly came in two waves. First, the volcanic ash itself blocked out the sun, and secondly, the effects from the sulfuric acid aerosols sprayed out of the volcano also reduced how much light made it down to earth from space.

First, volcanic ash definitely can’t stay in the air for years, it eventually settles to Earth. Original estimates of how long the ash from Toba could stay in the air were 3 to 6 months (Rampino & Self, 1993). This is why researchers claimed that “conditions of total darkness could have existed over a large area for weeks to months” (Rampino et al., 1988). However, some research has shown that ash from other large volcanic eruptions can settle to earth in less than a single day (Rose & Durant, 2011). For example, during Krakatoa’s eruption, total darkness around the volcano lasted less than a day (Simkin & Fiske, 1983). Therefore, the claim of total darkness for months under the ash clouds is probably wrong.

However, sulfuric acid can stay in the air for years. We know this because of an ice core sample from Greenland that showed multiple years of increased sulphuric compound levels in the atmosphere following the eruption of Toba (Zielinski et al., 1996). It’s been claimed that this ice core showed six years of raised sulfur levels, and that’s where the claim of six years of volcanic winter came from (Ambrose, 1998). However, there’s a problem with that theory…

The claims that sunlight was harshly reduced due to the sulfuric acid from the volcanic eruption primarily come from two sources (Rampino et al., 1988; Robock et al., 2009). But both of these studies based their visible optical depth calculations on a model of sulphuric aerosols in the atmosphere that was 20, 50, or even 100 times higher than what is considered to be the correct amount today (see Yost et al., 2018). In other words, yes, there was sulfur in the atmosphere, a lot of it, enough to register in Greenland ice cores, but probably not enough to noticeably dim the sun for a prolonged period of time. Krakatoa’s eruption caused abnormal-looking sunsets for three years (Simkin & Fiske, 1983). However, conditions of noticeably dimmer sun during the day did not last nearly as long. In other words, the six years of volcanic winter is almost certainly false, due to the ash falling out of the sky quickly, and there being a lot less sulfur than originally theorized. The claim gets a 1/5. There definitely was some darkening of the skies, though, and any humans alive to see that were probably extremely spooked.

PLUMMETING TEMPERATURES — 4/5

The estimates of global temperature drop of 8 to 17 degrees Celsius that I gave in the story are probably overestimates (Robock et al., 2009). Those estimates are based on assumptions of high-levels of sulphuric compounds in the atmosphere, which as we already discussed, are overestimates.

Other estimates given are that the worldwide temperature plunged 3–5 degrees Celsius (Rampino & Self, 1993), or even less, around .8 degrees Celsius (Timmreck et al., 2012) or .9 degrees Celsius (Oppenheimer, 2002). There is some physical evidence of a small temperature change. An investigation of the temperature in East Africa at the time, based on cores of sediment pulled up from the bottom of Lake Malawi revealed no evidence of a catastrophic change in temperature, at least not in East Africa, but the authors concluded that there was a small dip in temperature, around 1.5 degrees in magnitude — a dip that probably did not cause a significant volcanic winter (Lane et al., 2013). The effects of the temperature changes were described by one group of researchers as a “discomfort, but not a real challenge for survival” (Timmreck et al., 2012).

We know that volcanoes can lower global temperatures a little bit, as evidence from other volcanic eruptions has shown us.

Perhaps the best-documented climate effects from a volcanic eruption occurred in 1815, which caused the 1816 “year without a summer.” The volcanic eruption of Mt. Tambora, also in Indonesia, was the largest known volcanic eruption of the last millennium (Rampino, 2002). Temperatures dropped worldwide to the extent that crops partially failed around the world, including in Europe, North America, India, and China (Pfister & White, 2018). The coldest temperatures in meteorological history for the month of July were recorded in parts of the United States, and snow fell all summer long in Switzerland, leading to dangerous avalanches (Pfister & White, 2018).

There was also a major volcanic event in the year 536, but as you can imagine there are fewer reliable records to go off of when it comes to how the volcano affected the climate. However, using tree ring growth, researchers have determined that there was a period of abnormally low temperatures following that eruption too, because the trees at the time didn’t have very good years of growth (Büntgen et al., 2016). A scholar from back then named Procopius wrote that “the sun gave forth its light without brightness, like the moon, during the whole year.” and another scholar named Cassiodorus wrote about “strange” weather including “a summer without heat” (Newfield, 2018). The abnormal climate combined with a plague that may have been related resulted in the year 536 being declared “the worst year to be alive” in human history by one researcher (Gibbons, 2018).

If both of those volcanoes could make summers cold, and the Mt. Toba eruption was many times larger, then it stands to reason that Mt. Toba could have caused temperatures to plummet for at least a little while in some regions. The amount that the temperature dropped is probably not huge, but even a small dip can affect life on earth, as we will discuss in a minute. This claim gets a 4/5.

TRIGGERED AN ICE AGE — 0/5

There was a cold period for about a thousand years following the eruption of Mt. Toba (Mauelshagen, 2018), but those two things were probably mostly independent of each other. See, when Toba erupted, the climate had already been cooling off for about 100 years (Yost et al., 2018). And even under modeled scenarios of extreme amounts of sulfur compounds injected into the atmosphere, researchers wrote that “No matter what the amount of SO2, there is no evidence for ice age initiation” (Robock et al., 2009). There is evidence that a volcanic eruption can cause glaciers to advance slightly due to lower temperatures (Pfister & White, 2018), and it has been theorized to have a similar effect on sea ice (Rampino & Self, 1992). However, there isn’t enough evidence to say that such cold temperatures due to the volcano itself persisted for more than a few years, not enough for an ice age. This claim gets a 0/5.

DYING PLANTS, FOREST FIRES, & DECREASED RAIN — 5/5

There is evidence that there was a dying off of some plant matter following the Toba supereruption. When researchers looked at core samples from Lake Malawi in Africa, they found evidence that plants had died off in East Africa. This was especially true for higher elevation forests and grasslands — cold-sensitive plants probably suffered from the relatively short period of rapid cooling that actually occurred (Yost et al., 2018). They also found evidence in the form of microscopic charcoal that there had been some increase in forest fire activity in a period of otherwise low fire activity, and evidence of reduced rainfall following the eruption (Yost et al., 2018).

Other evidence for reduced rainfall following large volcanic eruptions comes from the eruption of Tambora, which was followed by an extreme drought in August in the United States. The water cycle was disrupted in other places causing extreme floods or droughts and sometimes both in back-to-back months. Crops such as fruit and grain were heavily disrupted by the lower temperatures, ruining crops globally (Pfister & White, 2018). Additionally, the volcanic eruption of 536 correlates with famines and droughts recorded in Chinese history (Newfield, 2018).

Additionally, there is some evidence from fossilized soil that some areas in India that used to be home to many trees were replaced by grasses following the Toba eruption (Williams et al., 2009). Similarly, models indicated that there would have been fewer trees and more grasses in Africa as well as a result of the eruption (Timmreck et al., 2012). In other words, the scenario described in the Toba Catastrophe Theory of a bunch of wild vegetation dying off and burning (Rampino & Ambrose, 2000) thanks to decreased sunlight, temperatures, and rainfall (e.g., reduced precipitation as described in Robock et al., 2009) is probably at least partially correct!

However, the apparent dying off was less extreme than the estimated effect of all of the trees dying (Marshall, 2013). Another core sample study (Jackson et al., 2015) found no evidence for an ecosystem disturbance of algae, which is a climate-sensitive ecological indicator. Overall, this claim gets a solid 5/5 because it has good physical evidence of the described events.

DID THE VOLCANO CAUSE SPECIES OF MAMMALS TO GO EXTINCT? — 0/5

This claim is completely unsupported. I went down a large rabbit hole trying to chase down where this claim came from, and found that mistakes were made in interpreting the research of other researchers. Turns out there’s no concrete evidence whatsoever. The closest that anyone has come is pointing out that the fact that there are species of animals that are on some Indonesian islands, but not Sumatra where Toba is, and the distribution of species looks kind of funny, but it’s very far away from concrete evidence of extinction (see the annotated reference for Wilting et al., 2012). This claim gets a 0/5.

WAS THERE A HUMAN POPULATION BOTTLENECK DUE TO THE VOLCANO? — 1/5

The researchers who believe in a human population bottleneck following the eruption of Mt. Toba have very little evidence to bring to the debate other than genetic modeling. And even that evidence is imprecise. I’ll explain. Geneticists can estimate how few humans were left alive at some point in history based on a few things. The mutation rate of different kinds of genetic information, such as DNA, the average length of each reproductive generation, or how old ancient people were when they had babies, and how similar genetic information is between different groups of people. Broadly speaking, what these studies show is that humans are remarkably similar to one another when it comes to our genetic code. The fact that we are so similar to each other is evidence that our species either hasn’t been able to mutate into a bunch of different descendant species of humans. The fact that we haven’t turned into different descendant species suggests some possibilities. Perhaps ancient humans were really good at passing genes between different regional populations of humans (interbreeding between groups) and this prevented us from mutating into different species. Or, perhaps our species is really young and only evolved recently, so there hasn’t been enough time for us to mutate yet. Or, perhaps there was a genetic bottleneck in which only a small number of humans survived. We don’t know for sure which of these is true, but it seems likely that there was a point in time in which there weren’t very many humans. However, having only 40 humans left is impossible. That did not happen. Why? Due to something called “minimum viable population size,” forty humans would not be nearly enough to repopulate the earth — if at any point there had only been 40 humans left, we would have gone extinct because of a lack of genetic diversity (Traill et al., 2007). It’s just math! 10,000 humans, or even just a few thousand, is a much more realistic number.

A commonly used statistic in scholarly sources is that a few thousand humans were left alive following the eruption due to the resulting climate change that caused cold and famine. The most common number that I saw was 10,000 people, which seemed to originally come from a 1972 paper (Haigh & Maynard-Smith, 1972) that had nothing to do with volcanoes, but was trying to estimate how few humans there would have needed to have been in order to explain a homogeneous pattern in human haemoglobin. The authors settled on 10,000 as a possible answer to a mathematical equation that they wrote and then modeled. The number 10,000 also emerged in a 1993 paper (Harpending et al., 1993) where it was popularized in an article in Science (Gibbons, 1993). The number 10000 then made its way to a 1998 paper (Ambrose, 1998) that tried to link the volcano to the population decline. But importantly, that 10,000 number was built using the genetic evidence that was available in 1972. Newer genetic evidence has not supported this 10,000 people or fewer following the Toba eruption hypothesis. In fact, it points in the opposite direction in two ways.

First, there probably was a human population bottleneck, but we have no idea when in human history it happened (Hawks, 2000; Watkins et al., 2001; Harpending & Rogers, 2000; Jorde et al., 1998). There are too many unknowns to pin down a date or link it to the Toba super-eruption. Secondly, the number of humans during the bottleneck has been more recently estimated to be more like 30 thousand, although I don’t have a convincing source on that number either (Prothero, 2018)!

Believers tried to argue that previous articles had “consistently identified” an “expansion from a very small population size in Africa” (Ambrose, 2003). But this wasn’t true. It’s like they tried to claim that there was lots of evidence that X was true, but when you actually looked at the supposed evidence, it actually said “Either X or Y might be true” (Harpending & Rogers, 2000) or “ If we assume X, then Z might be possible” (Takahata et al., 2001).

Another statistic that shows up on the internet frequently is that as few as “40 breeding pairs” of humans or sometimes just “40 humans” were left.

This “40” statistic seems to come from a theoretical paper published in 1986 (Jones & Rouhani, 1986). Importantly, that estimate had nothing to do with the Toba supervolcano, and it was part of a series of numbers thrown out by the authors as “little more than an informed guess.” Not only did they say that 40 was a possible number, but they also wrote that 2, 6, 600, and 4000 were other possible numbers. Basically, they just tried to solve an algebra problem by popping in different numbers and then seeing what happened, regardless of how realistic their generated scenarios were. They even wrote that it was possible that there was only a single breeding couple of humans for a period of 60 years. Just because that’s a possible solution to your equation doesn’t make it true at all.

Two of those numbers, 40 and 600 then showed up without citation in a 1994 paper with a graduate student as a lead author, perhaps helping to explain the neglect for correctly citing a source (Sherry et al., 1994).

Then, a highly speculative paper from 2000 shared some of these previous estimates of the human bottleneck, but it did so incredibly badly (Rampino & Ambrose, 2000). Not only did it not realize that the two estimates of 40 people were actually from the same estimate, but it also incorrectly cited where the original 40 number came from, giving credit to an entirely different paper that had entirely different numbers. It was very confusing.

From there, the number 40 made its way into a book called “The Violinist’s Thumb” where the author neglected to cite where the number 40 came from (Kean, 2012).

Following that, it made its way onto an NPR blog, clearly marked opinion, by Robert Krulwich, where he repeated the number “40” and then cited Kean’s book. From there, the number 40 exploded, appearing in magazines such as smith journal and Vox, and of course showing up as a “fun fact” on places like Reddit and Pinterest. In other words, that number 40 is based on misquoted, misattributed, misunderstandings of misapplied science to misaligned algebraic equations of mis-estimates of human genetic diversity from several decades ago that has been misleadingly cherry-picked. Nobody ever actually calculated that Toba killed all but 40 humans, as is often repeated as a “fun fact” on the Internet. It’s straight-up incorrect.

Researchers have claimed that there is some good genetic evidence for a human population bottleneck somewhere between 30,000 and 130,000 years ago, but also that there was good evidence that no bottleneck had occurred within the past several hundred thousand years (Harpending & Rogers, 2000). One source even claimed that the bottleneck occurred millions of years ago (Hawks et al., 2000).

Evidence against a cataclysmic event included the fact that life of hominids such as humans seemed to go on uninterrupted in some places of the world including in India (Petraglia et al., 2007) and in South Africa (Smith et al., 2018; See also discussions in Lane et al., 2013; Yong, 2018; Yost et al., 2018)

So, the Toba catastrophe theory is probably way overstated. The temperature didn’t plunge very much or for very long due to the volcano, and there were enough humans left to continue on our genetic lineage which means there were probably several thousand at the least. 40 humans left on earth huddled together to survive on an icy world without seeing the sun for years is a great story, but it’s probably just that, a story.

Unfortunately, the existing popular works about the Toba catastrophe are poorly done. A podcast episode just released this year for a show called “Natural Disasters” made a bunch of inaccurate claims. For example, it says “over 75,000 years ago” which is wrong, it claims that humans were in Indonesia during the eruption, which is also wrong because humans weren’t there until 73 ka — 63 ka. Claims that “the food chain was disrupted and humans died off in massive numbers, which was reflected in our fossil record” but this is highly speculative: no anatomically modern human fossils have been found from the Toba eruption period in the area around the volcano, and the genetic bottleneck is just a theory and NOT a fossil record. Claimed that humans had bountiful crops 74,000 years ago in Indonesia, including coffee and rubber… but humans didn’t discover agricultural farming that long ago, and coffee and rubber did not grow in Indonesia at that time. I assume they took the crop list of Indonesia straight from a Wikipedia page instead of researching the history of the crops (Leonard & Johnson, 2020).

Science communicators need to stop sacrificing truth for wild clickbait claims about unbelievable facts — we need to admit when we don’t know something for sure, because that’s often the case in science and history.

Watch the video about this article over at https://youtu.be/cPMjMDzimVQ

References

Ambrose, S. H. (1998). Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans. Journal of Human Evolution, 34(6), 623–651. https://doi.org/10.1006/jhev.1998.0219

*According to Yost et al., 2018, this was the first paper to formally propose the Toba catastrophe theory. Proposed that the catastrophe caused such a severe bottleneck in the human population that it resulted in a founder effect on genetic diversity, explaining why Asians, Africans, and Europeans look different.

Ambrose, S. H. (2003). Did the super-eruption of Toba cause a human population bottleneck? Reply to Gathorne-Hardy and Harcourt-Smith. Journal of Human Evolution, 45(3), 231–237. https://doi.org/10.1016/j.jhevol.2003.08.001

* Horrible paper. Mis-cites or Misleads in at least 6 places, including claiming that Rampino & Self 1992/1993 claimed a six-year volcanic winter (when they absolutely did not). They also write that “Determining the duration of a bottleneck is extremely difficult because a comparatively short, extremely severe bottleneck cannot be differentiated from a longer, less restricted one.” — which shoots a hole in their own theory of being able to estimate how small the size of the population bottleneck was (For example, Rampino & Ambrose, 2000 repeat the bogus “40” humans claim, AND mis-cite where that number came from.

Acharyya, S. K., & Basu, P. K. (1993). Toba ash on the indian subcontinent and its implications for correlation of late pleistocene alluvium. Quaternary Research. https://doi.org/10.1006/qres.1993.1051

*Showed that Toba deposits on the Indian continent are commonly 1–3 meters high, often 2–5m on the East coast (2500 km from the source), and also wrote that the dispersal pattern of the ash was in a “broadly northwesterly dispersal pattern.” Wrote: “The thick and extensive ash bed in the Indian subcontinent thus appears to be reworked Toba ash which has been contemporaneously redeposited from a wide catchment area and thereby thickened within the restricted depositional basins.”

Brooks, M. (2020). Devolution. Penguin Random House.

*A book about sasquatch fleeing a volcanic eruption and encountering humans. Fiction.

Büntgen, U., Myglan, V. S., Ljungqvist, F. C., McCormick, M., Di Cosmo, N., Sigl, M., … Kirdyanov, A. V. (2016). Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD. Nature Geoscience, 9(3), 231–236. https://doi.org/10.1038/ngeo2652

*Discussion of the effects following the 536 eruption, including the Justinian plague.

Chesner, C. A., Rose, W. I., Deino, A., Drake, R., & Westgate, J. A. (1991). Eruptive history of Earth’s largest Quaternary caldera (Toba, Indonesia) clarified. Geology, 19(3), 200–203. https://doi.org/10.1130/0091-7613(1991)019%3C0200:EHOESL%3E2.3.CO;2

*An estimate of the size of the eruption.

Choi, C. Q. (2013, April 29) Supervolcano not to blame for humanity’s near-extinction. Livescience. https://www.livescience.com/29130-toba-supervolcano-effects.html

*Focuses on Lane et al., 2013’s research about how there’s no evidence for extreme climate change due to Toba at their excavation site in Africa.

Costa, A., Smith, V. C., Macedonio, G., & Matthews, N. E. (2014). The magnitude and impact of the Youngest Toba Tuff super-eruption. Frontiers in Earth Science, 2(16). https://doi.org/10.3389/feart.2014.00016

*An estimate of the size of the magma and ash sent off by Toba.

Gathorne-Hardy, F. J., & Harcourt-Smith, W. E. H. (2003). The super-eruption of Toba, did it cause a human bottleneck? Journal of Human Evolution, 45(3), 227–230. https://doi.org/10.1016/S0047-2484(03)00105-2

*A paper that refuted Ambrose, 1998 — which Ambrose replied to in Ambrose, 2003. Claims that a bottleneck probably happened at some point, but there’s no evidence that it occurred due to Toba. Claims that the direct destruction of the volcano was minimal [❤50 km estimate]. Points out that there is little evidence for extinction events following the volcano (and Ambrose replies to this by claiming that he never said that there were extinctions).

Gibbons, A. (1993). Pleistocene population explosions. Science, 262(5130), 27–29. https://doi.org/10.1126/science.262.5130.27

*A write-up of the 10,000 humans left after a bottleneck theory, focusing on Harpending et al., 1993’s work.

Gibbons, A. (2018, November 15). Why 536 was ‘the worst year to be alive.’ Science Magazine. https://www.sciencemag.org/news/2018/11/why-536-was-worst-year-be-alive

*A write-up of recent research into the year 536.

Haigh, J., & Maynard Smith, J. (1972). Population size and protein variation in man. Genetical Research, 19(1), 73–89. https://doi.org/10.1017/S0016672300014282

*This paper may have been the first to throw 10,000 humans into the ring as a possible size of the population during the supposed genetic bottleneck, although it uses that number to solve a math equation that was written by the authors, meaning that huge assumptions were made about how genetics worked from then until now.

Harpending, H., & Rogers, A. (2000). Genetic perspectives on human origins and differentiation. Annual Review Of Genomics And Human Genetics, 1(1), 361–385. https://doi.org/10.1146/annurev.genom.1.1.361

*This paper concludes that “Several loci indicate that the human population passed through a bottleneck — a period of small population size. These loci seem to support the GOE hypothesis. Yet other loci indicate just as strongly that no bottleneck has occurred within the past several hundred thousand years. Any attempt to use genetic data in unraveling human history must deal with the discrepancy between these sets of loci.” — but despite these equivocal findings, Ambrose, 2003, tried to cite this paper as evidence for a clear-cut genetic bottleneck occurring around the time of the Toba eruption. Seriously, Ambrose just made a bunch of stuff up as he went along.

Harpending, H. C., Sherry, S. T., & Rogers, A. R. (1993). The genetic structure of ancient human populations. Current Anthropology, 34(4), 483–496. https://doi.org/10.1086/204195

* Posits the Weak Garden of Eden hypothesis for human origins. Did not calculate how many humans were left following a bottleneck, but did throw out some wild guesses about population density.

Hawks, J., Hunley, K., Lee, S. H., & Wolpoff, M. (2000). Population bottlenecks and Pleistocene human evolution. Molecular Biology and Evolution, 17(1), 2–22. https://doi.org/10.1093/oxfordjournals.molbev.a026233

*Argues that there was not a recent population bottleneck in humans because our genetics don’t reflect that happening. Also estimated a potential bottleneck could have occurred two million years ago.

Hernandez, R. D., Hubisz, M. J., Wheeler, D. A., Smith, D. G., Ferguson, B., Rogers, J., … & Muzny, D. (2007). Demographic histories and patterns of linkage disequilibrium in Chinese and Indian rhesus macaques. Science, 316(5822), 240–243. https://doi.org/10.1126/science.1140462

*See Williams et al.

Jackson, L. J., Stone, J. R., Cohen, A. S., & Yost, C. L. (2015). High-resolution paleoecological records from Lake Malawi show no significant cooling associated with the Mount Toba supereruption at ca. 75 ka. Geology, 43(9), 823–826.

*Claimed that significant cooling in East Africa following the Toba eruption was unlikely

Jones, J. S., & Rouhani, S. (1986). How small was the bottleneck? Nature, 319(6053), 449–450. https://doi.org/10.1038/319449b0

*Comes up with some POSSIBLE numbers for a POSSIBLE human genetic bottleneck, including the “40” number as one example, and also the “600” number repeated by Sherry et al., 1994 — and a bunch of other numbers too! Paper has nothing to do with Toba.

Jorde, L. B., Bamshad, M., & Rogers, A. R. (1998). Using mitochondrial and nuclear DNA markers to reconstruct evolution. BioEssays, 20(2), 126–136. https://doi.org/10.1002/(SICI)1521-1878(199802)20:2%3C126::AID-BIES5%3E3.0.CO;2-R

*Incorrectly used as evidence for Ambrose, 2003’s argument that there was a recent bottleneck in human population. Actually, this paper gives a range of estimates, some of which are way before and way after Toba.

Kean, S. (2012). The Violinist’s Thumb. Random House.

*Repeats the “40” humans claim without citing anything. Probably got the numbers from Rampino & Ambrose, 2000.

King. (n.d.). Volcanic Explosivity Index (VEI) Measurement Scales for Natural. Retrieved June 19, 2020. http://geology.com/stories/13/volcanic-explosivity-index/

*Shows a diagram of the different VEI sizes, including Toba

Koulakov, I., Kasatkina, E., Shapiro, N. M., Jaupart, C., Vasilevsky, A., El Khrepy, S., … Smirnov, S. (2016). The feeder system of the Toba supervolcano from the slab to the shallow reservoir. Nature Communications, 7. https://doi.org/10.1038/ncomms12228

*Claims that Toba has a mechanism that produces “a shallow crustal reservoir that is directly responsible for the supereruptions.” Claims that if the eruption were to happen today, it would “drastically alter human life.” Says that it is true that the explosion triggered changes in the global biosphere and climate, but that the consequences have been overestimated by the proponents of the Toba catastrophe theory. Also: “this volcano system may generate strong eruptions in the future.”

Krulwich, R. (2012, October 22). How Human Beings Almost Vanished From Earth In 70,000 B.C. NPR: Krulwich Wonders. https://www.npr.org/sections/krulwich/2012/10/22/163397584/how-human-beings-almost-vanished-from-earth-in-70-000-b-c

*Repeats the “40” humans claim, cites Kean book.

Lane, C. S., Chorn, B. T., & Johnson, T. C. (2013). Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka. Proceedings of the National Academy of Sciences of the United States of America, 110(20), 8025–8029. https://doi.org/10.1073/pnas.1301474110

*Found volcanic ash in Africa from Toba, and also lack of evidence for a dramatic temperature change following the event. Found evidence for a 1.5 degree drop, but not a 4ish degree drop.

Leonard, K. & Johnson, T. (2020, April 9). Toba supervolcano [Audio podcast]. https://www.stitcher.com/podcast/parcast/natural-disasters/e/68695217

*Podcast episode about the Toba supervolcano that makes some weird errors. For example, it says “over 75,000 years ago” which is wrong, it claims that humans were in Indonesia during the eruption, which is also wrong because humans weren’t there until 73 ka — 63 ka. Claims that “the food chain was disrupted and humans died off in massive numbers, which was reflected in our fossil record” but this is highly speculative: no anatomically modern human fossils have been found from the Toba eruption period in the area around the volcano, and the genetic bottleneck is just a theory and NOT a fossil record. Claimed that humans had bountiful crops 74,000 years ago in Indonesia, including coffee and rubber… but humans didn’t discover agricultural farming that long ago, and coffee and rubber did not grow in Indonesia at that time. I assume they took the crop list of Indonesia straight from a Wikipedia page instead of researching the history of the crops.

Louys, J. (2007). Ecology and extinction of Southeast Asia’s megafauna [Doctoral dissertation, University of New South Wales]. Retrieved from unsw.edu.au.

*This article says “The Toba super-eruption (~74kya) is unlikely to have been responsible for any of the megafauna extinctions of the Late Pleistocene.” but WIlliams et al. cites it as evidence for a Toba eruption extinction anyway.

Luke (2012, November 7). Story of a supervolcano. Smith Journal. https://www.smithjournal.com.au/blogs/history/story-of-a-super-volcano

*Repeats the “40” people bullshit. Cites Krulwich.

Marshall, M. (2013, April 29). Life after a supervolcano: It exists, but it’s no fun. (Retitled: Supervolcano eruptions may not be so deadly after all). New Scientist, 218(2915). https://www.newscientist.com/article/dn23458-supervolcano-eruptions-may-not-be-so-deadly-after-all/

*Reports on the Lane et al., 2013 study that cast doubt on the Toba catastrophe theory.

Mauelshagen, F. (2018). Migration and Climate in World History. In S. White, C. Pfister, & F. Mauelshagen (Eds.) The Palgrave Handbook of Climate History (pp. 413–444). Palgrave Macmillan. https://doi.org/10.1057/978-1-137-43020-5_31

*Summarizes what climate scientists believe about the Toba eruption on page 417.

Newfield, T. P. (2018). The climate downturn of 536–50. In S. White, C. Pfister, & F. Mauelshagen (Eds.) The Palgrave Handbook of Climate History (pp. 447–493). Palgrave Macmillan. https://doi.org/10.1057/978-1-137-43020-5_32

*Discusses the climate changes due to the 536 volcano.

Oppenheimer, C. (2002). Limited global change due to the largest known Quaternary eruption, Toba ≈74 kyr BP? Quaternary Science Reviews, 21(14–15), 1593–1609. https://doi.org/10.1016/S0277-3791(01)00154-8

*Argues against the Toba catastrophe theory like this: “What kinds of impact might the eruption have had on contemporary human populations? Can any credence be given to suggestions that the eruption precipitated a crash in human population numbers? While the arguments proposed by Rampino and Ambrose (2000) and Ambrose (1998) are plausible, they are not yet compelling because, in addition to the problems in estimating the global and regional climatic impacts of the eruption, it is hard to compare a fairly robust date for the YTT eruption itself, with controversial and uncertain dates for the putative demographic bottleneck. Furthermore, the timing of the YTT is at the limit of radiocarbon dating, perhaps holding out limited hope of advances coming from archaeology. Resolving the sequences of events and the relationships between cause and effect is difficult enough for the Late Bronze Age ‘‘Minoan’’ eruption of Santorini, a mere 3.5 kyr ago.” Noted the direction that the ash travelled on the wind: “The dispersal of the ash cloud across the South China Sea may point to eruption during the northern hemisphere summer monsoon when south-westerly winds prevail at low- to middle-tropo- spheric levels, transporting ash from lower parts of the co-ignimbrite clouds.” Claims that “Toba ash on the eastern coast of India is found in several metre-thick layers within alluvial sections and with grain sizes of a few millimetres (Acharyya and Basu, 1993). These considerable thicknesses, however, reflect post-deposition reworking.”

Oppenheimer, S. (2012). A single southern exit of modern humans from Africa: Before or after Toba? Quaternary International, 258, 88–99. https://doi.org/10.1016/j.quaint.2011.07.049

*Shows uncertainty in whether humans had even left Africa before the Toba supereruption (suggests that they left at 72 ka while Toba happened earlier at 74 as) — although it is still possible that humans were in Asia before the eruption based on the 95% confidence interval (57–87 ka 95% confidence interval). Writes that human fossils from this period have not been found in India, and other archaic hominids may be responsible for the stone tools found in India straddling the Toba ash layers. There is “no fully convincing evidence older than Toba.”

Petraglia, M., Korisettar, R., Boivin, N., Clarkson, C., Ditchfield, P., Jones, S., … & Roberts, R. (2007). Middle Paleolithic assemblages from the Indian subcontinent before and after the Toba super-eruption. Science, 317(5834), 114–116. https://doi.org/10.1126/science.1141564

*Evidence that humans lived in India before and after the supervolcano, based on their stone tools left behind above and below the ash layer.

Pfister, C. & White, S. (2018). A year without summer, 1816. In S. White, C. Pfister, & F. Mauelshagen (Eds.) The Palgrave Handbook of Climate History (pp. 551–561). Palgrave Macmillan. https://doi.org/10.1057/978-1-137-43020-5_35

*Discusses the Tambora volcanic eruption of 1816

Piper, K. (2019, July 25). The man who wants to save humanity from nuclear winter. Vox. https://www.vox.com/future-perfect/2019/7/25/20707644/nuclear-winter-famine-apocalypse-allfed

*Repeats the “40” nonsense. Cites Krulwich.

Prothero, D. R. (2018). When humans nearly vanished: The catastrophic explosion of the Toba volcano. Smithsonian Institution. https://books.google.com/books?id=opJLDwAAQBAJ&pg=PA91&lpg=PA91&dq=40+%22breeding+pairs%22+toba&source=bl&ots=etQp3EwIVO&sig=ACfU3U19jwAQRGviqt4lXZ8EZQUhluIy0g&hl=en&sa=X&ved=2ahUKEwjBpJqj1JDqAhUBH80KHbtBCq0Q6AEwDHoECAoQAQ#v=onepage&q=40%20%22breeding%20pairs%22%20toba&f=false

*p.91 mentions the “40 breeding pairs” nonsense. Also, other numbers like 30,000 with no source!

Rampino, M. R. (2002). Supereruptions as a threat to civilizations on earth-like planets. Icarus, 156(2), 562–569. https://doi.org/10.1006/icar.2001.6808

*Extensively cite their own research group’s simulations in order to make their claims more believable. Try to make speculation seem like fact, such as how much vegetation died off following Toba. Claims “The Toba aerosols apparently persisted for up to 6 years in the upper atmosphere (Rampino and Self 1992, 1993, Zielinski et al. 1996a)” and “All above-ground tropical vegetation would have been killed by sudden hard freezes, and a 50% die-off of temperate forests is predicted from hard freezes during the growing season (Rampino and Ambrose 2000, Sagan and Turco 1990),” both times citing themselves.

Rampino, M. R., & Ambrose, S. H. (2000). Volcanic winter in the Garden of Eden: The Toba supereruption and the late Pleistocene human population crash. Special Paper of the Geological Society of America, 345, 71–82. https://doi.org/10.1130/0-8137-2345-0.71

*A really badly done paper that mis-cites other papers in misleading ways. Steals the “40 individuals for two centuries” estimate without giving credit to the correct source (which is Jones & Rouhani, 1986). Extends Ambrose, 1998, to include a few new things like how the Toba catastrophe would have killed many plants, severely damaged tropical plants, and increased wildfires because of woody material leftover from dead plants. Has a speculative section called “Possible environmental and ecological effects of the Toba eruption.”

Rampino, M. R., & Self, S. (1992). Volcanic winter and accelerated glaciation following the Toba super-eruption. Nature, 359(6390), 50–52. https://doi.org/10.1038/359050a0

*This paper is pretty much identical to Rampino & Self, 1993.

Rampino, M. R., & Self, S. (1993). Climate-volcanism feedback and the toba eruption of ∼74,000 years ago. Quaternary Research, 40(3), 269–280. https://doi.org/10.1006/qres.1993.1081

*Estimated that volcanic dust can probably stay in the air for 3–6 months. Claimed that the eruption could have been “injected efficiently” into both hemispheres. Theorized that the increased snow cover from lower temps could have reflected additional sunlight. Theorized a 3-degree global cooling and a larger decrease for higher latitudes in the summer months (e.g., 15 degrees colder in Quebec in the summer).

Rampino, M. R., Self, S., & Stothers, R. B. (1988). Volcanic winters. Annual Review of Earth and Planetary Sciences, 16, 73–99. https://doi.org/10.1146/annurev.ea.16.050188.000445

*Estimated how much light was blocked out by the Toba eruption

Roberts, R. G., Storey, M., & Haslam, M. (2013). Toba supereruption: Age and impact on East African ecosystems. Proceedings of the National Academy of Sciences of the United States of America, 110(33), 3047. https://doi.org/10.1073/pnas.1308550110

*Argued against Lane et al., 2013’s findings. Didn’t say much, just that the science is still uncertain.

Robock, A., Ammann, C. M., Oman, L., Shindell, D., Levis, S., & Stenchikov, G. (2009). Did the Toba volcanic eruption of ∼74 ka B.P. produce widespread glaciation? Journal of Geophysical Research Atmospheres, 114(10), 1–9. https://doi.org/10.1029/2008JD011652

*Simulations of global cooling following the Toba eruption. Claims global precipitation decreased 30–60% for several years. Claims significant climate recovery within a decade, an initial drop of 8 to 17 degrees celsius, and “No matter what the amount of SO2, there is no evidence for ice age initiation.” [So Toba didn’t cause an ice age, but just happened to erupt during one?]. Concluded that the eruption could have produced a colder climate for about a decade and serious effects on plant and animal life, but not a glacial advance. “We find no evidence that the 1000-year cold period seen in Greenland ice core records was directly generated by the Toba eruption, although the temporal inference shown by Zielinski et al. [1996] is certainly quite intuitive.”

Rose, W. I., & Chesner, C. A. (1987). Dispersal of ash in the great Toba eruption, 75 ka. Geology, 15(10), 913–917. https://doi.org/10.1130/0091-7613(1987)15%3C913:DOAITG%3E2.0.CO;2

*Cool pictures of Toba ash from scanning electron microscopes. Called Toba one of Earth’s largest eruptions.

Rose, W. I., & Durant, A. J. (2011). Fate of volcanic ash: Aggregation and fallout. Geology, 39(9), 895–896. https://doi.org/10.1130/focus092011.1

*Claims that volcanic ash from large eruptions can settle to earth in less than a day.

Sheehan, D. P. (2019, August 27). The loudest sound in history: Krakatoa erupted on this date 136 years ago. The Morning Call. https://www.mcall.com/news/local/mc-nws-krakatoa-anniversary-20190827-udxuiu2zmzf7xpubkmg6uju3pm-story.html

*Called Krakatoa the loudest sound in history.

Sherry, S. T., Rogers, A. R., & Harpending, H. (1994). Mismatch distributions of mtDNA reveal recent human population expansions. Human Biology, 66(5), 761–775. https://www.jstor.org/stable/41465014

*Gives estimates based on genetic modeling of human population levels and expansions; probably stole numbers without citing where they came from. Makes a lot of assumptions and is based on old science.

Sigl, M., Winstrup, M., McConnell, J. R., Welten, K. C., Plunkett, G., Ludlow, F., … Woodruff, T. E. (2015). Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature, 523(7562), 543–549. https://doi.org/10.1038/nature14565

*Discusses the eruption of 536, mentions tree-ring analyses which are cool.

Simkin, T., & Fiske, R. S. (1983). Krakatau 1883 — a centennial retrospective on the eruption and its atmospheric effects. Weatherwise, 36(5), 244–254. https://doi.org/10.1080/00431672.1983.9930158

*Discussion of the effects of Krakatoa (e.g., how far away the explosion was heard).

Smith, E. I., Jacobs, Z., Johnsen, R., Ren, M., Fisher, E. C., Oestmo, S., … Marean, C. W. (2018). Humans thrived in South Africa through the Toba eruption about 74,000 years ago. Nature, 555(7697), 511–515. https://doi.org/10.1038/nature25967

*Evidence that humans were fine before, during, and after the supposed Toba Catastrophe.

Symons, G. J. (1888). The Eruption of Krakatoa: And Subsequent Phenomena. Trübner & Company. https://books.google.com/books?id=Vk8PAAAAYAAJ

*Symons edited the book, but 13 authors are credited as part of the “Krakatoa committee.” Contains graphs of barometers that were recording during the eruption.

Takahata, N., Lee, S. H., & Satta, Y. (2001). Testing multiregionality of modern human origins. Molecular Biology and Evolution, 18(2), 172–183. https://doi.org/10.1093/oxfordjournals.molbev.a003791

*A paper incorrectly cited by Ambrose, 2003 as evidence for a recent human population bottleneck. Actually, this paper makes up a hypothetical scenario in which a bottleneck happened, and then extrapolates from there — in other words, it isn’t evidence for Ambrose’s theory.

Thalmann, O., Fischer, A., Lankester, F., Pääbo, S., & Vigilant, L. (2007). The complex evolutionary history of gorillas: insights from genomic data. Molecular biology and evolution, 24(1), 146–158. https://doi.org/10.1093/molbev/msl160

*See Williams et al.

Timmreck, C., Graf, H. F., Zanchettin, D., Hagemann, S., Kleinen, T., & Krüger, K. (2012). Climate response to the Toba super-eruption: Regional changes. Quaternary International, 258, 30–44. https://doi.org/10.1016/j.quaint.2011.10.008

*Suggests that the Toba eruption produced a smaller climate cooling than previously estimated, with their lower-end sulfur magnitude model suggesting a global drop of .8 degrees celsius following the eruption of Mt. Toba

Traill, L. W., Bradshaw, C. J. A., & Brook, B. W. (2007). Minimum viable population size: A meta-analysis of 30 years of published estimates. Biological Conservation, 139(1–2), 159–166. https://doi.org/10.1016/j.biocon.2007.06.011

*Estimates that humans (and other species) have minimal viable population sizes of around 3577–5129 (that’s the 95% confidence interval), indicating that having less than 3577 or so humans left would lead to extinction, and therefore, it is not possible for Toba to have caused such an extreme bottleneck.

Watkins, W. S., Ricker, C. E., Bamshad, M. J., Carroll, M. L., Nguyen, S. V., Batzer, M. A., … Jorde, L. B. (2001). Patterns of ancestral human diversity: An analysis of Alu-insertion and restriction-site polymorphisms. American Journal of Human Genetics, 68(3), 738–752. https://doi.org/10.1086/318793

*A paper incorrectly cited by Ambrose, 2003 as evidence that a bottleneck happened recently in human history. Actually, this paper just shows that a bottleneck probably happened at some point in time, but gives no specifics on when, and definitely does not link it to the volcanic events of Toba.

Westaway, K. E., Louys, J., Awe, R. D., Morwood, M. J., Price, G. J., Zhao, J. X., … Sulistyanto, B. (2017). An early modern human presence in Sumatra 73,000–63,000 years ago. Nature, 548(7667), 322–325. https://doi.org/10.1038/nature23452

*Estimates that anatomically modern humans were in Sumatra, Indonesia 73,000–63,000 years ago based on analyses of sediment/cave formations and animal teeth found near some human teeth found in the 1800s.

Williams, M. A., Ambrose, S. H., van der Kaars, S., Ruehlemann, C., Chattopadhyaya, U., Pal, J., & Chauhan, P. R. (2009). Environmental impact of the 73 ka Toba super-eruption in South Asia. Palaeogeography, Palaeoclimatology, Palaeoecology, 284(3–4), 295–314. https://doi.org/10.1016/j.palaeo.2009.10.009

*Evidence that the Toba eruption killed off many trees in India: “Stable carbon isotopic analyses of fossil soil carbonates directly beneath and above the Toba ash from sites in the Son and Narmada valleys of central India, located∼3400 km NW of Toba, indicate a change from forests before the Toba eruption to open or wooded grassland ecosystems after the eruption.” Theorizes that a large-mammal extinction event in southeast Asia could have also been driven by Toba. This paper makes similar misleading citations as does the original Ambrose papers from 1998 and 2003 (and considering that Ambrose is a coauthor, that’s not surprising). Specifically, the Thalmann et al., 2007 and Hernandez et al., 2007 papers that were cited as evidence of genetic bottleneck in “other species” — neither of these papers mentions an appropriately-timed bottleneck OR the Toba eruption. The Thalmann paper describes gorillas as “a constant, long-term population size” and makes no estimate within the timeframe of the Toba eruption for a population disruption (80 to 200 ka for the end of gene flow between West and East gorillas vs. 74 ka for Toba). The confidence interval for the macaque population decline in India in the Hernandez paper is entirely outside the range of the Toba eruption (72 to 21 ka for the macaque population decline in India vs. 74 ka for Toba). Ambrose has a habit of just throwing random citations into a pile as if they proved his point, when in fact they do not help prove his point. Additionally, Williams et al. cites Louys, 2007 as evidence that the “regional extinction of 12 southeast Asian large mammal species (Louys, 2007), may have been initiated by this event…” — However, Louys actually wrote: “ The Toba super-eruption (~74kya) is unlikely to have been responsible for any of the megafauna extinctions of the Late Pleistocene.”

Wilting, A., Sollmann, R., Meijaard, E., Helgen, K. M., & Fickel, J. (2012). Mentawai’s endemic, relictual fauna: Is it evidence for Pleistocene extinctions on Sumatra? Journal of Biogeography, 39(9), 1608–1620.

*Incorrectly claims that Louys, 2007 said that Bos javanicus went extinct on the islands because of the Toba eruption. Louys did not say that.

Yong, E. (2018, March 12) Supervolcano goes boom. Humans go meh? The Atlantic. https://www.theatlantic.com/science/archive/2018/03/supervolcano-goes-boom-humans-go-meh/555356/

*Piece about Smith et al. 2018 that focuses on how humans were fine through Toba and the catastrophe hypothesis is bunk.

Yost, C. L., Jackson, L. J., Stone, J. R., & Cohen, A. S. (2018). Subdecadal phytolith and charcoal records from Lake Malawi, East Africa imply minimal effects on human evolution from the ∼74 ka Toba supereruption. Journal of Human Evolution, 116, 75–94. https://doi.org/10.1016/j.jhevol.2017.11.005

*Takes down the Toba Catastrophe Hypothesis with analyses of phytoliths and charcoal, as well as a discussion of climate change.

Zielinski, G. A., Mayewski, P. A., Meeker, L. D., Whitlow, S., & Twickler, M. S. (1996). A 110,000-yr record of explosive volcanism from the GISP2 (Greenland) ice core. Quaternary Research, 45(2), 109–118. https://doi.org/10.1006/qres.1996.0013

*The ice core analysis that showed a 6-year H2SO4 deposition after the Toba eruption.