Quintessence: echoes across science

Posted on 13 October, 2013 by Metageologist

I’ve been reading up on the story about cometary material found in Libya (odd pebble is cometary material fallen to earth). My plan to write about it myself has run into the desert sands – I have nothing new to add. However reading the source paper has taken me off on a tangent, inspired by the word quintessence. It is a word that rolls off tongue rather nicely. It also has so many interesting meanings that I want to talk about them a little.

Non-scientific

Quintessence has been defined1 as:

A thing that is the most perfect example of its type; the most perfect embodiment of something.
A pure substance.

For these everyday meanings you might use it like you do the more common word quintessential, for example to make a science fiction film seem profound: “Hope, it is the quintessential human delusion, simultaneously the source of your greatest strength, and your greatest weakness”

Proto-scientific

The word comes from Medieval french, meaning ‘fifth essence’. At this time, attempts to understand the natural world were often framed in terms of Ancient Greek concepts, based on the works of authors such as Aristotle. The world was seen as being made up of 5 elements, or essences. Fire, earth, air and water covered the everyday. The fifth, ‘highest’, essence, also known as aether was contained within everything and was also the material that made the heavenly bodies.

Hindsight is a wonderful thing. Having the benefit of hundreds of years of scientific progress, grounded in experimental observation, it is tempting for us to be dismissive of our ancestors ‘mistaken’ opinions. Take alchemy for example. Isaac Newton, has (largely since his death) been seen as the quintessence of a rational scientific genius. However in reality he was a keen student of alchemy (and of other occult studies).

Alchemy (like astrology) came from genuine efforts by intelligent people seeking to understand the world. There is an interesting thread in contemporary studies of the history of science tracing the connections between the concepts of modern science and these older beliefs.

The aether

One example of this is the scientific concept of aether. To the Ancients, it was linked to the heavens and the quintessence underlying everything. In alchemy the name became mixed up with the idea of elixirs or medicines. In 1730 German scientist W.G. Frobenius changed the name of chemical compound ‘sweet vitriol’ to ether, a name now attached to a whole related group of organic compounds. Having found a good way to manufacture ‘sweet vitriol’ he was keen to sell it – perhaps naming it ether (thereby invoking a heavenly universal medicine) was simply marketing. Ether has since been uses as a solvent, an anaesthetic and a narcotic to use while driving from LA to Las Vegas to find the American Dream.

The name aether also resonates strongly in the world of physics. Seventeenth Century studies of optics, notably by Christiaan Huygens led to theories explaining light in terms of waves. If light involved waves, then some substance must be present for the waves to act on. This was known as the aether. Only with the Twentieth Century understanding of the weirdness of wave-particle duality (light is caused by little particles (photons) that behave in wave-like ways) was the concept of aether no longer required.

Modern physicists attempt to reconcile observations of the incredibly large (cosmology) and unimaginably small (particle physics). Gaps between theory and observation lead them to infer the existence of dark energy, one proposed form of which is given the name of quintessence. Whether this a purely hypothetical concept that will go the way of aether is not something a mere ex-geologist can speculate on.

And finally

What about the Libyan cometary material, this interesting pebble found in the Sahara?

The scientists involved were only given a gram of material which they then subjected to a whole battery of analytical procedures2. One of these involved heating it and analysing the gases that come off. Typically chondritic meteorites – chunks of the primordial solar system – contain a component known as Q, short for quintessence. This is thought to represent the ‘ambient gas of the early solar nebular’. The solar nebular is the cloud of dust, gas and ice from which the everything in the solar system (including you and everything you’ve ever seen) was born. There is no quintessence in the Libyan fragment, suggesting it did not form in the inner Solar System, but can only have formed far out where there is little gas at all. Out there, between 30 and 50 times further from the sun than we are, is comet country.

Another name for the gas know as quintessence is ‘planetary 1’, which is as dull a name as you could imagine. I salute the person who named it quintessence. Science rests on the precise use of technical terms, all of which have names. Giving them beautiful names with resonance and historic significance keeps us in touch with the poetic. The Ancient Greeks yearned to understand the mysteries of the world around us. Using words like quintessence reminds us that we are driven by exactly the same quintessentially human urge.

What’s in a (geological) name?

Posted on 8 October, 2013 by Metageologist

Devil’s toenail

The Earth Sciences are often about bringing order to the wonderful overflowing complexity of the natural world. The geological way of doing this is often to classify. A hill-side of rocks, often a bewildering mess to an amateur (or first year student) can with experience be tamed. It can be mapped as a series of rock units, made up of rock types containing minerals. It may contain fossils that can be assigned a species which may reveal which period of geological history it was formed in. All of these things have names.

Some of these names shed light on the history of the science or the difficulties of classification. Some are poetic, some generate schoolboy sniggers. Let’s meet a few.

Minerals

Common minerals were first named by non specialists. Quartz comes from an old root word meaning hard, Feldspar is the German for ‘mineral of the field’ and garnet is from an old french word meaning ‘dark red’. However most are named by scientists, after mineral properties, places or people.

Some names are the victim of changing language use. Welsh and Dick are normal names, likewise the town of Cummington doesn’t cause surprise. However the habit of adding -ite to the end of mineral names has created much amusement for students learning the properties of welshite, dickite or cummingtonite.

James B. Thompson, Jr postulated a whole new way of stacking structures in silicate minerals. When examples were found, in his honour they were given the awesome name of jimthompsonite and even better, clinojimthompsonite: my favourite mineral names.

Dead things

There are manymany fossils and so lots of names. As a student I was powerfully of the opinion that there were too many. My favourite name? Fossil bivalves called Gryphaea have the old popular name of “Devil’s toenails“.

Time

Let’s start with the Geological Periods:

(Pre)Cambrian – latin name for Wales
Ordovician & Silurian – latin names for Celtic (Welsh) tribes
Devonian – English country of Devon. People from Devon sometimes refer to themselves (correctly) as Devonian, even when they are younger than 400 million years old.
Carboniferous – ‘coal-bearing’ in Latin. The industrial revolution was ignited by burning coals from rocks this age
Permian – ancient Russian kingdom of Permia
Triassic – tri = three. In some areas has three distinct layers
Jurassic – Jura mountains, just north of the Alps
Cretaceous – Latin for ‘chalk bearing’
Tertiary/Quaternary or Palaeogene/Neogene/Quaternary/Anthropocene – lots of Latin

Personally, the whole Latin thing leaves me cold. The names I like best are where another language comes in. Take the original British subdivisions of the Ordovician: Tremadocian, Arenig, Llanvirn, Llandeilo, Caradoc and Ashgill. These are mostly based on Welsh placenames. Even pronouncing them correctly is a challenge for a non-Welsh speaker.1

The Geological Periods were named by British Victorian gentlemen and reflect their preoccupations (latin, the Romans) and their focus on European geology2. Further subdivisions of time have been changed over the years to better reflect global geology. One major purpose of dividing geological time is to assign ages to rocks. Changing the detailed subdivisions to match specific events (the first appearance of fossil x) makes sense as does naming the new subdivision after areas that contain good sedimentary sequences of this age.

Following this practice, most of the Welsh Ordovician names above have been replaced, by names based on Swedish, Chinese, Australian and American locations. The same applies across the geological timescale. It’s hard not to see this change of names as also tracking the flow of power and scientific innovation around the globe, away from Europe.

Pieces of rock

Rocks mean different things to different people. To a kitchen fitter or an architect, marble and granite are very general terms for hard and soft polishable rocks. Geologists are more precise. Even geologists are precise to a different degree -a rock that might reasonably be mapped as a ‘granite’ might properly be described as a granodiorite.

A type of rock may have a whole series of names. Coal-bearing rocks of Carboniferous age often have a layer of pure quartz sandstone beneath the coal. To geologists an orthoquartzite or arenite this rock was known to miners as a ganister or seatearth, and was used to line furnaces. It formed as an ancient soil horizon so it could also be called a palaeosol.

My favourite rock name is pseudotachylite, which means roughly ‘fake volcanic glass’. It forms when movement along deep fault zones heats rock so much that it melts. It’s other obsolete name is ‘flinty crush rock’ which would be a good name for a musical sub-genre.

Packages of rock

On large scale, geologists identify packages of rock and give them names. Supergroups, groups, formations, units – there are a lot of names for the different types of packages – and countless examples. Packages tend to be named after the place they are best exposed – they have local character.

As a monoglot anglophone (who likes technical terms) I treasure every exposure to non-English words. As a British geologist who had an Irish field area, I’ve heard a lot of gaelic places names, both Scottish and Irish. The Bennabeola Quartzite, the Ariskaig Tillite, the An-t-sron and Ghrudaidh Formations, the Currywongaun Gabbro. Mmmm, close my eyes and I can taste the Guinness (or whisky).

South Africa is a complicated place, with place names based on English, Afrikaans and a variety of African languages. Rock package names pick up this diversity. The ancient Barberton rocks contain the Moodies, Onverwacht and Fig Tree Groups plus the Schoongezicht Formation. The Pongola Supergroup contains the Sinqeni Formation, which contains a Zulu click-sound in the middle that takes a lot of practice to master.

The most poetic set of rock unit names I know come from Yosemite Valley in California. Diorite of North America, Dikes of the Oceans, Tonalite of the Gray Bands – they are the most evocative names for a bunch of granite that I’ve ever heard.

The Great Ordovician meteor shower

Posted on 30 September, 2013 by Metageologist

Between Mars and Jupiter, 470 million years ago, there was a massive collision between two 100km-sized chunks of rock – this solar system’s biggest bang of the last billion years. It created a massive cloud of smaller fragments. Some of these landed on the earth, falling at a rate at least a hundred times greater than at present. These fragments can be found today in sedimentary rocks from that time. More speculatively, this shower from space has been linked to two dramatic events – a set of vast fossil landslides plus a major event in the history of life – a landslide of new fossils known as the Great Ordovician Biodiversification Event.

Grains raining from the sky

Meteorite from Thorsberg Quarry. Image from Lund University

It started with unsightly green blobs in a Swedish limestone quarry. Discarded by the quarrymen, these odd lumps are fossil meteorites. These are incredibly rare – something most geologists will never see. This may explain why they were only identified correctly in the 1980s (by amateur geologist Mario Tassinari). Since then, researchers – notably Birger Schmitz of Lund University in Sweden – have found over 90 meteorites from this one quarry1.

Recognising this as something remarkable, they started looking for other evidence in other rocks of the same age. Dissolving limestone in acid, they were able to pick out tiny grains of chromite. This mineral forms on the earth, but using chemistry they were able to show that these grains could only have come from space. Such grains have been found in China2 and Russia, as well as Sweden. Tiny tiny meteorites (fabulously called cosmic spherules) have been found in Scotland3 and Argentina.

Reading up on this, I was rather excited to realise that rocks of the same age are found in Ireland. I was writing a post about the use of heavy mineral analysis in these rocks, showing variation in the number of chromite grains! Had I just made an exciting connection? The Irish papers interpret the chromite as coming from an eroded ophiolite – were they actually from space? I did some maths and as it turns out, no they weren’t. Maths can be cruel.

The rocks in Sweden contain so many meteorites for two reasons. As well as forming at a time when huge numbers were falling to earth, they also formed extremely slowly. Known as a condensed sequence, each centimetre thickness represents tens of thousands of years of deposition. Sitting on a flat sea-bed, little or no sand was washed in so only limestone mud, a sort of organic dandruff, settled to the sea-bed. That and fragments of a space collision, scientific manna from heaven. The Irish rocks built up thick layers a thousand times faster as sand, gravel and mud spilled from the hills above. If you processed 1000kg of Irish rock, you’d expect to find only a few grains of extraterrestrial chromite. So the many grains counted in the Irish studies could have contained only a small number of space chromites. The most likely small number being zero.

Look to the heavens

All the best scientific stories reach across different disciplines. Studies of the chemistry of this space dust show it to come from a single source – the meteorites are all of a well-known type called “L-chondrites”. Using isotopes, Schmitz was able to assess how long his chromite grains had been floating in space, exposed to cosmic rays. The younger the rock layer, the longer the exposure. All of this suggested the middle Ordovician meteorite shower was caused by a single event, fracturing a large body into many pieces. Independently, a 1964 study of L-chondrite meteorites had identified a ‘shock age’ of around 470 million years ago – providing independent evidence for the collision. Using spectral analysis of asteroids (looking very very carefully at their colour), its possible to identify pieces of the original body that remained in stable orbits – the Gefion family of asteroids. L-chondrites even today form about 20% of the meteorites that reach earth.

Hidden impacts?

In the Earth Sciences, things tend to follow a power-law distribution. For example, tiny earthquakes are very common, moderate ones common, large rare, and very large earthquakes are very rare. Smash a huge asteroid into pieces and you might expect the size of the fragments to follow a power-law distribution . On earth we’ve found the uncountable numbers of tiny chromite grains and a lot of small meteorites – it is entirely reasonable to assume that a few crater-forming-size fragments also hit the earth in the Ordovician.

They’ve found a few – the Lockne crater in Sweden and the Osmussaar breccia in Estonia4 are pretty solidly linked to large impacts by L-chondrite bodies in the Ordovician. However craters are remarkably hard to preserve so maybe there aren’t that many more to find. What is needed is traces of the impacts that affected a large area and might be found in sedimentary rocks of this age.

John Parnell of Aberdeen University has suggested5 that the many impacts at this time caused an unusual series of ‘mass wasting’ events on continental margins – essentially a series of massive landslides. These are not small things – the Buttermere formation6 in England’s Lake District is a 1500m thick sequence of sediments that was sheared and folded as they shifted down an ancient sloping sea-floor. There are another 13 similar deposits of middle Ordovician age around the world.

Sample of the Buttermere Formation Olistostrome from Ian Stimpson

Not everyone agrees7. Massive landslide deposits are not uncommon – the middle Ordovician was also a time of sea-level fall, something that can cause continental slopes to become unstable. Further, all of the examples formed in tectonically active areas. The Lake District rocks formed on a volcanic arc near a subduction zone. There would have been plenty of large earthquakes to trigger a landslide – there is no need to invoke a nearby meteorite impact to explain it.

Change the history of life?

Could the mid-Ordovician impacts have changed the course of life on earth? In 2008 Birger Schmitz 8 linked them to a dramatic event in the history of life: the Great Ordovician Biodiversification Event (GOBE). Spanning 25 million years, this event saw an unprecedented increase in the number of species of fossil animals. Schmitz and co-workers tracked both fossil abundance and the record of extraterrestrial debris on a bed by bed scale.

Figure 3 from Schmitz et al. (2008). “The results are based on bed-by-bed collections at eight localities. Note the dramatic increase in biodiversity (black line) and high extinction (blue line) and origination (red line) levels following the regional Volkhov–Kunda boundary, that is, the same level where extraterrestrial chromite appears and Os isotopes change”

How could the things be linked? They talk of “impact-related environmental perturbations” which feels like one of those CIA euphemisms for murder, meaning as it does “sterilising large areas of the earth”. The key point is, not all of the earth. Once the dust has settled, a habitat empty of inhabitants is a fantastic opportunity for nearby animals to move into. By creating a more varied environment, impacts can actual increase the diversity of species, they argue.

It’s a lovely idea,but one that is far from being proven. Other environmental factors (very high sea-level, lots of islands, changing climate) or biological changes (the GOBE sees planktonic life become important for the first time) are equally or more plausible. In a great recent podcast overview of the GOBE, David Harper (second author on the paper) refers to the meteorite link only after discussing all the other possible causes, and does so with a slightly apologetic tone.

Showing that the GOBE and the remarkable flux of space debris happened at the same time is not enough. What is required is to prove the causal relationship. This is a very hard thing to do. Maybe all of the proposed causes were each partly responsible?

The History of the Earth is history

The Earth Sciences are unusual in being partly a study of past events. Sometimes perhaps we should think more like scholars of human history. Historians studying, say, the origins of the First World War are aware of the importance of multiple causes. The tensions of imperialism, the aggressive German foreign policy, even the inflexibility of railway timetables – are just some of the many proposed ’causes’ of this terrible war. Any educated discussion of this topic would acknowledge that many things were contributory in some way. There is no single ’cause’ for WW1.

Was the extinction of the dinosaurs caused by the eruption of the Deccan Traps or the Chicxulub impact? Yes. Surely both are part of the story in some way9? Thinking a little like historians, the quest to prove one cause is right and the other wrong seems a little foolish.

The events of the middle Ordovician are less dramatic but illustrate the same point. Maybe we will never know if the Buttermere olistrostrome was caused by a meteorite impact, or just a large earthquake and low sea-level. But maybe we will. Historians derive new insights from studying archives of old documents. Our archive is the world itself (and beyond). New rocks, new techniques and novel combinations of the two may one day give more dramatic insights on the Great Ordovician meteor shower.

References

I first heard of the Great Ordovician meteor shower from Ted Nield’s excellent book Incoming, which I recommend to you as it covers all manner of marvellous meteoric matters.

I’ve tried to put web links to copies of the original papers in the footnotes. Formal references to key papers are below.

Schmitz B., Tassinari M. & Peucker-Ehrenbrink B. (2001). A rain of ordinary chondritic meteorites in the early Ordovician, Earth and Planetary Science Letters, 194 (1-2) 1-15. DOI: 10.1016/S0012-821X(01)00559-3
Parnell J. (2008). Global mass wasting at continental margins during Ordovician high meteorite influx, Nature Geoscience, 2 (1) 57-61. DOI: 10.1038/ngeo386
Meinhold G., Arslan A., Lehnert O. & Stampfli G.M. (2011). Global mass wasting during the Middle Ordovician: Meteoritic trigger or plate-tectonic environment?, Gondwana Research, 19 (2) 535-541. DOI: 10.1016/j.gr.2010.07.001
Schmitz B., Harper D.A.T., Peucker-Ehrenbrink B., Stouge S., Alwmark C., Cronholm A., Bergström S.M., Tassinari M. & Xiaofeng W. (2007). Asteroid breakup linked to the Great Ordovician Biodiversification Event, Nature Geoscience, 1 (1) 49-53. DOI: 10.1038/ngeo.2007.37

Power and postboxes in Sonning-on-Thames

Posted on 22 September, 2013 by Metageologist

I live in the Thames Valley, an attractive area of England found to the west of London. It is generally an affluent place, but it contains little spots, clustered near the river, where you can almost smell the vast amounts of money and power. The Fat Duck (the “world’s best restaurant”) is in the little village of Bray, site of a small cluster of Michelin stars that shine on the conspicuously expensive cars in the car parks.

The village of Sonning-on-Thames is a little like Bray. It has swanky restaurants from which middle-aged men stagger with women young enough to be daughter (but no-one would wear a skirt *that* short to a family meal). Unlike Bray, it is not just a temple to gastronomy but also a place where normal people live. But the landscape here has been shaped by its powerful residents, modern and old.

I live in adjacent Woodley, separated from Sonning by the Great Western Railway. This marvel of Victorian engineering spread out from London’s Paddington station (home to marmalade-loving bears) west to Wales, Bristol and far-flung Cornwall. The ground-breaking engineer Isambard Kingdom Brunel was adept at dealing with hills and valleys, but he was forced to back-down when faced with the Power of Property. In Berkshire, the Great Western Railway closely follows the river Thames, and the logical route into Reading would take it through Sonning. However, the local MP Robert Palmer1, owned land on the route, was opposed to the railway and refused to allow it through. The only solution was to make a more direct route into Reading, passing through the small hill above Sonning.

Sonning Cutting. Image from Pete Reed under Creative Commons.

Originally a tunnel was planned, like the one through Box Hill that was being built at the same time further west. However Sonning’s rocks are gravels and muds, sitting above the Chalk. These layers, the Reading Beds and London Clay are barely rock and too soft to take a tunnel. So Sonning Cutting was created, dug by hand over several years.

A lovely spot now, it had an inauspicious start. Several men were killed building it and within a few years it was the site of the world’s first major rail disaster. After heavy rain, a small landslide derailed the train and 8 people, travelling in an open Third class carriage were killed. A faint tang of death lingers still, even though it has been widened and the slopes safely un-steep and wooded. My favourite bridge over it had low sides with holes in it. Peer through it with a small boy and slow-moving train drivers would wave and toot. The large sign for the Samaritans suicide hotline was a sombre reminder why this is known as Suicide Bridge. Current modifications to increase the height of the sides (as part of electrification of the line) will remove a lovely view, but perhaps for the best.

I crossed the Cutting to visit Sonning recently to view a Postbox. It’s not a real one. It sits on the side of bridge, reachable only from the fast-flowing river Thames. From a distance it is a very convincing Royal Mail post box. What is its purpose? Is it a reference to the impending sale of the Royal Mail, being sold down the river? According to a friendly dog-walker, it is likely connected to a local pub – a similar one had appeared on the wall there recently. Who else but the landlord of the nearest pub would most benefit from the media attention and increased visitors this mystery post box has generated?

The bridge is ‘listed’, meaning it is protected by law. Sadly this means that any unauthorised changes must be removed. Friendly dog-walker and I agreed that this was a shame, the world should have more stylishly pointless things in it.

The media coverage of this anonymous piece of art was blighted by a modern powerful resident of Sonning. The BBC news article has Sonning resident Uri Geller centre stage. Famous for bending spoons, this “self-proclaimed psychic” told the BBC “he suspected it may have been placed there by the ghost of a small girl which reputedly haunts the bridge”.

If you walk a small distance from the bridge you encounter imposing fencing covered in keep-out signs. His massive house sits on the hill above, bringing to mind H. L. Mencken’s quote “Nobody ever went broke underestimating the intelligence of (the American) people”. On the river bank there is an absurd sculpture of a bent railway sleeper ‘bent by the power of the mind … inspired by Uri Geller’.

This lying piece of egomania was ‘donated to the people of Sonning’. A indication that they might not be entirely grateful comes from this wonderful sign on the imposing fence around his property.

Sonning has long been shaped by the powerful men who live there. I look forward to seeing more counter-balancing signs of the anonymous and the subversive sprout there.