Category Archives: impacts

Geology and myth

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As a word, myth has taken on negative connotations. False modern stories are dismissed as “urban myths”, myths are seen as old superstitions to be ‘busted’ by scientific truth. There are geologists who take a different view. Taking myth in its original sense – the stories by which pre-literate societies make sense of their world – they see it as a precious scientific resource, shedding light on dramatic but infrequent geological events that might otherwise go unrecognised.

Myths have traditionally been studied by those trained in ‘the arts’. They have been studied for their religious, or psychological or literary qualities. Looked at like this, they seem in opposition to a modern scientific world-view. At the most extreme, myths are either stories told by those ignorant of how the world really is, or insights into realities that transcend ‘reductive science’. Perhaps this tension between science and myth is not one that would make sense to the actual authors of the myths. They were intelligent and observant people trying to make sense of the world. They described events in terms of their world-view, (fighting gods and such-like) but that doesn’t mean they weren’t describing real events to the best of their abilities.

A glimpse of the ways in which pre-literate societies store practical information about geological events came with the 2004 Indian Ocean ‘Boxing Day’ tsunami. In some remote areas people survived because they climbed to high ground in advance of the tsunami hitting. They did so because they recognised the warning signs from their verbal folklore, which advised moving to high ground in such cases. Such an ability to transfer important information across generations is clearly valuable.  Perhaps this is going on in some myths, stories preserved from other pre-literate societies?

The Geological Society 2007 special publication Myth and Geology is a selection of papers from scholars grappling with this very question. The opening essay contains my favourite example of mythology that is clearly linked to a natural event; the Klamath Indians from Oregon in the US have a myth concerning a fight between the chief of Below World and the chief of the Above World. They hurled rocks and flames at each other and darkness covered the land. The fight ended when the chief of Below World was forced back into his kingdom. The hole where this happens remains – we know it today as Crater Lake, the site of a major volcanic eruption 6500 years ago. Human artefacts are found in the ash layers of this eruption so we can be certain that this myth is a modified eye-witness account.

Myth and Geology is full of stories like this. I want to pull out three themes – fossils, faults and impacts, leaving much of the book unmentioned.

Fossils and Myth

Dwarf elephant skull courtesy of Wiki Commons

Cyclops, brought to you courtesy of Wiki Commons

 

 

 

 

 

 

 

 

Before science came along with its amazing tale of life’s billions of years of twists and turns, what stories did we tell ourselves about fossils? Finding colossal bones of unfamiliar creatures, we told stories about fighting giants. Adrienne Mayor describes place names across the world based on the fossils found there. Native Americans were well aware of dinosaur track-ways, for example.  Agnesi, Di Patti and Truden take us to Sicily and describe how elephant skulls found there are likely the origin for the myth of cyclops: giants with a single eye in the middle of their forehead. Fossil echinoids are common in southern England. K. J. McNamara describe how they were know as fairy loaves or thunderstones and associated with magic. Today they can found in significant places in the walls of old churches.

Earthquakes and Myth

Major earthquakes are geologically common events all around the Pacific Rim and figure in the myths of that region. Ludwin & Smits compare traditions from pre-Columban cultures in Cascadia (close to Seattle, USA) with Japan. Their broad thesis is that even when expressed in symbolic language, myth and folklore describe geological events.

In both areas, earthquakes are explained in terms the movements of creatures of great power living underground. In Cascadia, stories are of struggles between a Thunderbird and a whale, in Japan – giant catfish. In North America, the folklore helps clarify recent seismic activity on the Seattle fault, and so sheds light on future hazards.

The Japanese material is from the 18th Century and is in the form of sophisticated pictures. My favourite has to be the one showing “courtesans and male workers of the elite brothel district” attacking a giant earthquake-causing catfish. A group of builders rushes in to defend the fish, as earthquakes bring them a lot of work.

A fairly well known piece of geomythology concerns the Delphic Oracle. Consulting oracles was a major political and cultural part of Ancient Greece, featuring frequently in Greek literature. The Oracle was consulted and then went into a special place to consult with the Gods, breathing vapours that arose from the ground. Recent geological work shows that the temple sits on a fault and that it is plausible that ethylene vapours were present. In a recent BBC Radio ‘In Our Time’ program on the Delphic Oracle this research was raised. An expert on Ancient Greece culture dismissed it in a word. She gave no reasons, perhaps showing the disdain towards science sadly so often found in British ‘Arts Graduates’.

Myth and cosmic impacts

I’ve talked so far about common, important but infrequent events. There is another set of events so uncommon that no-one living has witnessed one – major cosmic impacts, where a big chunk of space comes hurtling out of the sky. Massie & Massie write about a big dataset of myths from South America. They link myths that talk about ‘sky fall’ or ‘great darkness’ with Andean volcanic eruptions and associated ash clouds. Having established the usefulness of their data-set, they turn to another set of myths that talk of a ‘world fire’ with origins in the sky. They link a set around Argentina with a known impact site, Campo del Cielo. Other data, myths collected from the Brazilian Highlands and elsewhere can’t be linked to any obvious crater, but they speculate a link to an ‘air-burst’ where the impacting object doesn’t reach the ground, but does create enough energy to cause widespread burning.

This paper is only a part of the work Bruce Masse is doing. Looking at flood myths from around the world he proposes a link between them and a major cometary impact in the Indian Ocean. This would apparently put large volumes of water into the atmosphere, causing rain, plus massive flooding around the world.

Myth and belief

I’ve deliberately stuck to describing the work where the author is describing the myths of another culture. In these cases, the author has no emotional stake in the validity of the myth and they are objective. In the case of a Christians looking for Noah’s Ark, or the role of geological features in Hindu faith, I have my doubts that a person’s beliefs will not get in the way of a rational analysis of the facts </english understatement>.

One consequence of geomythology, this new way of looking at myths, is that it reduces the gap between us and humans in the distant past. To quote Myth and Geology it provides us “with a profound respect and appreciation for the observational powers of our ancestors”. A modern scientist describes natural phenomena in light of her world-view, no less than any myth-maker. With ‘science’ we have a fantastic, useful and sophisticated world-view that has been tested against reality for centuries. What a privilege! However, without the benefit of this body of knowledge and ways of thinking, are we modern people much different from our ‘primitive’ ancestors? After all, we all just want to make sense of the world, one story at a time.

Note, David Bressan has an excellent post on the whole Japanese catfish, earthquake thing, including pictures.

Hurled from the sky

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Since ancient times in China, special glass stones have been recognised. Called Lei-gong-mo, or “Ink sticks hurled from the sky by the thunder god” these are now known as tektites. These remarkable stones are found on the surface in a small number of areas (called strewn fields) around the world.

Two splash-form tektites (from http://en.wikipedia.org/wiki/File:Two_tektites.JPG)

Two splash-form tektites (from http://en.wikipedia.org/wiki/File:Two_tektites.JPG)

There are various types of tektite such as splash-form, ablated and layered. They are all lumps of extremely dry glass, often with distinctive shapes.

There is a trade in tektites and you can buy them on eBay. I’m tempted, but I gather fraud is a problem and I can never get over a feeling that they look like cat-poo.

How are they formed?

Tektites have been recognised for thousands of years. Geologist Charles Darwin* thought they were volcanic in origin, not unreasonable since volcanoes produce lots of glass. By the mid-Twentieth Century they were thought by many to be blebs of glass that had fallen through the earth’s atmosphere. Ablated tektites in particular suggest this. Look at the picture below- the central top area is the top of an originally spherical blob. The base was then melted again by friction as it fell through the earth’s atmosphere, the material being pushed up and around to form the distinctive shape. One idea was that the material originally came from the moon before falling to earth, but this was ruled out once actual lunar samples were collected: the geochemistry just didn’t match.

Aerodynamically shaped / ablated tektite (http://en.wikipedia.org/wiki/File:Australite_back_obl.jpg)

Tektites are now seen as resulting from large impacts on the earth’s surface that throw molten rock into space where it falls back, covering large areas. They are found in distinctive areas, strewn fields, nearly all of which have been associated with an impact crater. Within a strewn field, the age of the glass and the impact match, plus there is a size distribution, with large chunks near the impact and smaller tektites further away. Micro-tektites, also known as spherules (a purely descriptive name) may be found enormous distances away. Layers of micro-tektites are now being found in sedimentary rocks, particularly in the Archean (when impacts were much more common).

A recent paper by Kieren Howard in the Proceedings of the Geologists’ Association (doi:10.1016/j.pgeola.2010.11.006) provides a nice overview of modern thinking on tektites, drawing on numerical modelling of impacts. Melting of rocks within an impact crater is no surprise, the energies, and therefore temperatures and pressures produced by the impact are extremely high. What is less obvious is that melting happens in different ways. As the shock wave from the impact passes through the ground it can produce large volumes of melt. Most of this is mixed up with the fractured country rock to form melt breccias (pseudotachylites) and some is mixed up with rock fragments and thrown out to form a layer near to the crater (suevites). The rocks closest to the impact reach temperatures >5000°C, producing a mixed melt+vapour phase. This is ejected in high velocity jets travelling at ‘cosmic velocities’ (>11 km/s) that push away our planet’s puny atmosphere in a process called atmospheric blow-out. This means that small volumes of melt can effectively fly into space and then fall to earth – tektites!

Tektites are very very dry (< 0.05 wt % water) which is attributed to a process called “bubble-stripping”, where the water is lost as vapour under decompression. The dryness therefore is not related to the conditions under which the melt formed. Indeed Kieren Howard’s main argument is that tektites are especially common in impacts where the surface layers are particularly moist. He believes that the presence of water near the surface means that large volumes of especially high velocity melt can be produced.

Case of the missing crater

The biggest strewn field on the planet is the Australasian. This stretches from SE Asia through to Antarctica and is robustly dated at 0.803 Ma. The only problem is nobody knows where the crater is! An impact spread 10 million tons of glass across a huge area, but the only trace found to date is the tektites themselves. The usual pattern of size distribution in the strewn field points to SE Asia – there are lots of large (>1kg) tektites in Thailand, Cambodia and Vietnam but the expected big circular hole in the ground is not to be found. It is likely therefore that the impact was offshore and the crater has since been buried by more recent sediments. Another possibility is that the impact was oblique, at a shallow angle, and that there is a structure to be found that isn’t a classic circular crater. As you can imagine, the hunt is on, and Kieren Howard is part of it. Once he, or someone else, finds the source of these tektites, expect to hear about it. This is surely a story to capture the imagination of non-specialists (like journalists).

Drifting slightly off-topic, a related paper in Geology in 2008 made me the most jealous I’ve been for a long time. It documents finding micro-tektites in Antarctica, extending the Australasian strewn field even further (>400km). The authors sampled isolated mountains, surrounded by the Antarctic ice-sheet (nunataks). Basically they picked-up whatever sand was lying on the surface or tucked into joints and found little beads of glass – micro-tektites – in it. These landed 800,000 years ago and yet are just lying there waiting to found. Tektites in other areas, Australia say, have been buried and then uncovered, pitted by weathering and such-like. But in Antarctica nothing has happened for nearly a million years (or longer). Erosion is low because of very low precipitation and there are no other sources of sediment to bury the micro-tektites. They fell out of the sky and then nothing happened, until some Geologists came by. Other studies, using cosmogenic nuclide dating have shown that some rock surfaces in Antarctica are 2 or 3 million years old. This astonishes me every time I think about it, places like this just don’t feel like they belong on earth. Just to make that clear, the surface is 3 million years old, not the rock itself but the surface you can put your hand against. What’s more, scientists going to such places are the first human beings ever to go there (unless other scientists have been there before). I’m used to places that were scraped clean by glaciers 12,000 years ago, and continuously inhabited ever since. Visiting these other-worldly places on the very bottom on the world must be a very special experience indeed.

References

“Tektites in the Geological Record, Joe McCall, Geological Society of London, 2001” is a little old now but contains lots of details on tektites around the world, including all the detailed evidence supporting the impact origin of tektites.

http://tektites.co.uk contains lots of information and lovely pictures and is the best place to go next if you want more tektite fun.

Notes

* I know, I know, he is rather better known for his role in biology, but his training was as much geological as biological. Also the concept of Deep Time was vital to his development of his theory of natural selection. Without a knowledge of the geological evidence that the earth is rather older than 6,000 years, Darwin’s insight that species evolve due to small incremental changes doesn’t really make sense. Plus he was the first to explain the formation of coral atolls.