home

Project

Team

Research

Publications

Education

Media

Links

Sponsors

 

This page is designed for students and others interested in the ways we explore the impact of the Toba super-eruption on hominins (early humans) and environments 74,000 years ago. It includes answers to a series of questions commonly asked about the Toba super-eruption. A brochure in Telugu (the major language spoken in the Kurnool District of Andhra Pradesh, India) is available here.

What is a super-volcano?

What makes Toba so special?

What does a volcano have to do with human evolution?

What is archaeology?

How does archaeology help in understanding Toba's impact?

What other methods can help?

Why do scientists disagree about the impact of Toba?

Where can I get more information?

 

What is a super-volcano?

The terms ‘super-volcano’ and ‘super-eruption’ were first introduced by scientists and the media to describe the Toba eruption of 74,000 years ago. Previous terms such as ‘mega-eruption’ have also been used to describe the same phenomenon: volcanic eruptions far bigger than any occurring in recorded history (the past few thousand years). Other former super-volcanoes include Yellowstone (Wyoming, USA) and Oruanui (Taupo, New Zealand).

Super-eruptions are defined by the volume of material they release. Although there is no strict definition, in general an eruption that produces more than 300-400 cubic kilometers of tephra (fragments ejected into the air) may be considered ‘super’. This is quite a large volume of rock – it would be enough to cover all of Greater London beneath 210m of ash. The Toba eruption is estimated to have been perhaps eight times larger than this. By comparison, Mount St. Helens in 1980 erupted less than one cubic kilometer, and Krakatau in 1883 about 12 cubic kilometers.

For those who enjoy calculations, a formula has been developed to calculate the magnitude (M) of an eruption: M=log10(m) -7.0, where (m) is the erupted mass in kg, worked out from measurements taken on exposed deposits. Using this scale, super-volcanoes are those of magnitude 8 or larger, erupting more than one thousand million million (1015) kg of material. Toba was ten times bigger than this, and was therefore a magnitude 9 eruption.

There are two types of super-eruption. The first is an enormous outpouring of lava across a wide area – this releases a large volume of material and so qualifies as a super-eruption, even though it does not involve the huge ash clouds some people associate with ‘typical’ volcanoes. The second type is explosive, sending tephra across a wide area and causing tremendous local destruction. Both types release a large volume of gases as well as solid material, and these may have the greatest effect as they influence the atmosphere and potentially global climate.

[Return to menu]

What makes Toba so special?

Although dozens of super-volcanoes (greater than magnitude 8) have been recorded by geologists, only two are known to have erupted since the emergence of anatomically modern humans some 200,000 years ago in Africa. These are the Toba eruption in Sumatra (74,000 years ago) and the Oruanui eruption in New Zealand (26,500 years ago). While the Oruanui volcano was large, the fallout from the eruption was concentrated on the surrounding area, which was at the time uninhabited by humans. By contrast, the Toba eruption was five times as big as even the Oruanui event, and sent ash across a wide area that covers India and parts of southeast Asia, places that were inhabited by stone-tool making hominins. Even more importantly, the Toba eruption occurred at about the time that modern humans may have been starting to move out of Africa and the Middle East into other parts of the world. Added to this, observations suggest that it occurred during the initial stages of an ice age, and some scientists believe Toba may have contributed to this climatic swing.

[Return to menu]

What does a volcano have to do with human evolution?

Toba had erupted a number of times previously (one of these, about 840,000 years ago, was itself a super-eruption). What was significant about the event 74,000 years ago was the coincidence that an important period in human evolution was occurring at the same time. The Earth was already inhabited by a number of species closely related to us, such as Homo neanderthalensis (the Neanderthals) in Europe, and Homo erectus and Homo floresiensis (sometimes called the ‘hobbits’) in southeast Asia. All of these survived Toba, but some archaeologists have claimed that almost all the anatomically modern humans (our direct ancestors) were killed by the environmental effects the volcano caused, with the remaining people surviving in refuges in Africa. This scenario is based on data from genetics, and because it suggests that people were narrowed down from many to very few numbers, it is known as a genetic ‘bottleneck’.

The questions for human evolution therefore include:

·       Did Toba have a dramatic (global) environmental impact, significant enough to result in a genetic bottleneck? And how did this change the course of our evolution?

·       Were modern humans living in or dispersing across India at the time that the Toba ash fell, and if so were they killed off by the volcano and its climatic effects?

·       Were the hominins living in India non-modern, but they were killed off allowing modern humans an easy passage during a later dispersal?

A related question, but from a different perspective, is what would happen if a super-volcano were to erupt today? Can we learn lessons from the last time this happened that would help us survive?

[Return to menu]

What is archaeology?

Archaeology is the scientific search, recovery and interpretation of material evidence for past behaviour. Most archaeologists examine objects and sites created by modern humans (in the last few hundred thousand years), but archaeology also deals with human ancestors back to the time of the first stone tools, 2.6 million years ago in Africa. As a science, archaeological research involves creating hypotheses about how, why and when people lived in various parts of the world. These hypotheses are then tested against the evidence left behind by those people. This process usually involves a series of steps:

1.     Research in libraries and discussions with other archaeologists and local people helps us decide on an area where we may find evidence to test our hypotheses. This will depend on the question we want to answer, and is a very important stage as the following fieldwork stages are very time-consuming and often expensive.

2.     We go to our chosen field areas (in our case in southern and northern India), and search for indications that past humans or their ancestors lived in a particular place or site. This stage is known as survey.

3.     Once promising sites are identified, we very carefully dig holes to find buried material from earlier times (deeper objects are usually older than those closer to the surface). Detailed records are made of the sediments in which the artefacts are buried, as well as the location and condition of the artefacts themselves. This stage is known as excavation.

4.     The most time-consuming stage is the period of analysis and interpretation that follows the fieldwork, when all the data collected during survey and excavation are put together. As part of this process, a series of tests may be run on the recovered sediments to find out what the past environment was like, and samples such as charcoal are processed to provide dates for the different levels within a site.

5.     The final stage involves writing reports on our work and publishing these so that other archaeologists and scientists can see the work we’ve done and compare it to previously discovered information. These reports usually generate further hypotheses that will drive the next round of research, and the process begins again.

[Return to menu]

How does archaeology help in understanding the impact of Toba?

Much of the speculation about Toba’s impact on human evolution and dispersals is based on indirect evidence from genetics and environmental reconstruction. Archaeology allows us to recover and examine the direct evidence left behind by the early humans who were in India at the time that the ash fell. This information, especially the forms of stone tools and their presence or absence immediately above and below the ash layer in our sites, provides much more specific data about the impact of Toba than we can obtain from other sources. One of the additional benefits of an archaeological approach is that we can collect samples for dating and environment reconstruction at the same time as we recover human artefacts, tying these different strands of evidence together.

[Return to menu]

What other methods can help?

Other methods that work alongside archaeology include computer modeling of the way that Toba’s huge gas and ash cloud would have interacted with earth’s atmosphere, volcanological analysis of the ash or tephra itself to reveal details of the volcanic eruption (including the chemistry of the rock that was ejected and estimates of the length of the time over which the eruption occurred), and comparison of the evidence for a dramatic reduction in the numbers of humans at the time of Toba with records from other animal species to see if they were similarly affected. You can read more about some of these methods, along with others that out team is using, in our research page.

[Return to menu]

Why do scientists disagree about the impact of Toba?

The huge size of the Toba super-eruption 74,000 years ago has been known for many decades, but it is only in the past ten years or so that scientists have seriously begun considering the influence of this event on human evolution. We are therefore at the stage of collecting as much high-quality data on the natural environment and human responses to the eruption as possible, and as different scientists work with data from different sources there will be times when not all the data points to the same conclusions. More and more sources of information are being explored each year, including the climate records from gases trapped within northern hemisphere ice sheets, and sophisticated genetic analyses of living human populations to reconstruct past evolutionary trends. It is one of the most important features of science that theories and hypotheses can change as new evidence comes in, and this can lead to old ideas being replaced by new ones. We do not yet have all the answers, and in some cases (such as determining the species of humans living in India at the time of the eruption) we don’t even have the evidence required to make definitive statements. We can be sure, however, that each step is bringing us closer to solving the Toba mystery.

[Return to menu]

Where can I get more information?

The LINKS page of this website is a guide to other reliable places on the internet where you can learn about human evolution, archaeology and volcanoes. We will be adding to this page as our project progresses.

[Return to menu]

 

© 2009 M.Haslam & M.D.Petraglia, University of Oxford