Life on the Rocks: Islay and the Port Askaig Tillite

It’s been an interesting month for me – I’ve been studying a few fossil specimens which I’ve been meaning to get round to for most of the last two years, and starting to dabble in making some 3D reconstructions from them (on which more later, if it works). But summer is finally here, and that means it’s also been time for fieldwork.

This time, the adventure was to Islay, an island off the west coast of Scotland famous mostly for its whisky, but also (among a much smaller, more geologically inclined group of people), for its rocks. Islay has some globally important Precambrian rock successions with some amazing stories to tell, so when my friend Breandán asked me if I wanted to come on fieldwork with him there for a couple of days, I of course said yes.

Geological map of Islay, showing the Argyll Group (green), which contains the Port Askaig tillite and Bonahaven formation cap carbonate. Image by Mikenorton, via wikimedia commons.

Geological map of Islay, showing the Argyll Group (green), which contains the Port Askaig tillite and Bonahaven formation cap carbonate. Image by Mikenorton, via wikimedia commons.

Between 850 and 635 million years ago, in the Cryogenian period, Earth went through a series of massive glaciations, much more extreme than anything since. The last ice age, which we associate with beleaguered cave men hunting mammoths through the snow,  was a summer picnic by comparison with the Cryogenian, and has lasted for less than 3 million years with ice sheets restricted to areas close to the poles.  The longest of the Cryogenian glaciations, by contrast, locked most of the planet into an icy shell for around 60 million years, longer than the whole of the Jurassic Period.

Ice sheets reached down to very near the equator, leaving beds of glacial sediments and geochemical clues that the whole Earth was in the deep freeze. Some geologists suspect that the ice sheets might actually have covered the entire planet, creating what has been called a ‘Snowball Earth’ scenario. Islay has some of the best Cryogenian rocks in the UK, and is a key locality for studying this somewhat crazy time in Earth’s climatic history.

Like many other deposits from Cryogenian glaciations, the rock succession we looked at on Islay started with a thick glacial deposit called the Port Askaig Tillite, which is a thick, dark layer of mostly fairly fine grained sedimentary rocks, with a few much larger rock clasts embedded in it. Most of these were scraped and cracked off a continent by ice sheets which carried them out to sea before dropping them along with the rest of their much finer sediment load. Over that, in a succession of rocks called the Bonahaven Formation, is limestone – what is known as a ‘cap carbonate’, because it ‘caps’ the glacial rocks below like icing on a Christmas cake.

Breandán points out a dropstone in the Port Askaig tillite. These chunks of rocks were broken off the bedrock by ice sheets and deposited at sea.

Breandán points out a dropstone in the Port Askaig tillite. These chunks of rock were broken off the bedrock by ice sheets and deposited at sea.

All over the world, Cryogenian glacial deposits are topped with cap carbonate, and this poses puzzles of its own. We usually associate this kind of limestone formation with warm water conditions, not necessarily what we would expect in the periods of respite between massive glaciations. It’s been suggested that the Cryogenian glaciations only ended when something (volcanic eruptions, the release of methane from permafrost or methane hydrate from the deep seas, for example) pumped carbon dioxide into the atmosphere, triggering a strong greenhouse effect and effectively defrosting the Earth. If this is true, then the Cryogenian Period was a time of climatic extremes – not just intense and lasting cold, but intense heat too.

Cap carbonate in the Bonahaven Formation, over the Port Askaig tillite. Cap carbonates are thought to have developed in warm conditions when glaciations ended.

Cap carbonate in the Bonahaven Formation, over the Port Askaig tillite. Cap carbonates are thought to have developed in warm conditions when glaciations ended.

Understandably, given the science fiction flavoured subject matter and its vast scope, the Cryogenian is a buzzing area of research with a mass of unanswered questions. We are still wondering what caused the glaciations and how they ended. Work on Jupiter’s moon Europa, which is entirely covered with a thick shell of ice but has an ocean of liquid water underneath, shows that ‘Snowball’ scenarios are a real possibility, and poses interesting questions about life on other planets. Life got through the Cryogenian on Earth, so why shouldn’t we find it on a frozen moon of Jupiter, too?

Europa - A Snowball Moon.

Europa – A Snowball Moon.

We know that some microbial life must have survived the cold, since we have good evidence of fossil cells dating back to at least 1800 million years ago, well before the Cryogenian. This shouldn’t surprise us too much; microbes can live in Antarctic permafrost, so the idea of life surviving more or less permanent ice cover shouldn’t seem too implausible. On the face of it, life on a Snowball Earth sounds impossible, yet somewhere under all that ice the ancestors of all life on Earth today made a living.

Microbial structures (stromatolites) in the Bonahaven Formation. Microbes can survive in ice and

Microbial structures (stromatolites) in the Bonahaven Formation – descended from survivors of the most extreme climatic events since the origin of life, as you are.

Thanks to Breandán MacGabhann, of Edge Hill University, for allowing me to tag along on his fieldwork with my notebook and camera, and for arranging the route of said fieldwork to include five different distilleries. 

 

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When science meets storytelling

One of the most useful putdowns in science is to declare something a ‘just-so story’ – a pat explanation of an observation with little evidence to back it up. I have heard this term used, and used it myself, when discussing evolutionary biology, geology, psychology – and a quick Google suggests it’s common currency in a few other fields too. As an undergrad, my friends used to affectionately refer to palaeontology lectures as ‘storytime’. This never bothered me – the best science writers I can think of recognise that the history of life, with its highs and lows, its various jeopardies, its many mysteries and its long arc leading to ourselves and beyond, works well as an epic. But day-to-day, scientists can be somewhat suspicious of stories, with their vague implication of childish untruth. Scientists, we tend to think, deal only in facts.

This is odd, when you think about it. As a PhD student, I am gradually learning to build stories around new observations. Whether they know it or not, all scientists do this – after all, data has to be interpreted for it to be any use to us, and extrapolating from what we know to what we don’t (essentially, storytelling) is where new hypotheses come from. The quality of the hypotheses we test is limited by our ability to imagine what might be true, so an element of imaginative storytelling keeps science ticking over.

What’s more, scientists employ some of the techniques of real live storytellers, or at least they should. People have gathered together to listen to each other talk for thousands of years; it’s one of the most natural ways of spreading information. If you’ve sat through a few scientific talks or lectures, you’ll know that the best ones are often essentially stories, using a narrative to build tension, interact with their audiences or otherwise keep you interested. I’d never claim to be any expert at this myself, but it’s a thing I think about and work towards, because it is terrific when it works well.

And there is nothing like a good scientific anecdote for spreading information – Darwin musing over some distractingly delicious Galapagos tortoises, Cope and Marsh sabotaging each others’ dig sites and naming dinosaurs in each others’ (dis)honour, or, my own favourite, Apsley Cherry-Garrard, Edward Wilson and ‘Birdie’ Bowers crossing the Ross ice shelf in the middle of Antarctic winter to recover a few penguin eggs in the cause of developmental biology. Every scientific endeavour, from an undergraduate dissertation to the Curiosity mission, generates a new casebook of scientific comedies and tragedies. Most of these will remain private tales and snippets of science chat, but some will make history.

Stories of scientific obsessions and rivalries, lucky breaks, eureka moments, friendships and collaborations have lessons for researchers about the right and wrong ways to do science. I can even admit to getting the occasional bit of consolation from a good tale of epic failure by my safely famous scientific heroes when a new idea doesn’t work out. What’s more, it’s in the nature of good stories to travel well, and it helps if we recognise this, especially when we’re lucky enough to be talking about our work outside the research community.

As scientists, we worry about accuracy, reproducibility, objectivity – and we worry about ‘storytelling’ done badly, with overinterpreted data, or weak evidential support, or logical errors. Sometimes, we’re right to worry; much of science is, after all, an attempt to bring our theories about the world closer to the truth, not shuffle the evidence into stories we already have in mind. We dislike sketchy ‘just-so’ stories when they’re presented as valid conclusions, and quite right too. But while scepticism is healthy, I think we’re wrong to fear the odd tall tale.

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‘Don’t drink the water and don’t breathe the air’: A time-traveller’s guide to environmental proxies

Imagine you find yourself on a beach during the later half of the Ediacaran Period, around 550 million years ago, looking out towards a shallow sea. The sand underfoot is slightly sticky and slimy from a thin covering of microbial mats, but you’re not going to let a little ooze put you off – you’ve travelled a long way to get here and are thinking of taking a dip in a real, Ediacaran ocean to celebrate.

The question is, should you? Earth in the Ediacaran is a different planet after all – and this far back, the water could be highly acidic, it could be toxic, it could be clear and oxygenated or anoxic and reeking of rotten eggs. Is it safe to swim?

Worse than that, is it safe to breathe? Does the atmosphere contain enough oxygen to keep you alive, or is it a cocktail of potentially lethal gases? And even if the air is safe, what about the sunlight? Is there an ozone layer protecting you from solar radiation, or are you being gradually fried by your own home star?

We can’t study the ancient oceans and atmosphere directly, but there is another way. Environmental conditions, such as temperature, pH, or oxygen levels, influence the composition of the rocks which form in those environments. Millions of years later, we can measure chemical abundances, isotope ratios or the proportions of different elements relative to each other to reconstruct environmental conditions on the ancient earth.

These indirect measures are called proxies, and they are fantastically useful. For example, geochemical proxies have allowed us to investigate how Earth’s climate has changed over time, helping us to understand how we are influencing it now. They’ve also allowed us to investigate how the biosphere evolved, and how Earth’s environments have altered to accommodate – or extinguish – life.

Some proxies give a global signal, while others only tell us about local environments. Some work in the very distant past, while some are so prone to alteration that they can only accurately reconstruct environments in the comparatively recent past. We need to pick our proxies carefully to make sure they’re addressing the questions that really interest us, and where possible combine them so that the limitations of one can be compensated for by the strengths of another.

New environmental proxies are devised all the time, and many don’t gain broad acceptance for one reason or another – they might be too unreliable, too technically difficult or expensive to measure, or it might only be possible to apply them in very specific circumstances. But by combining multiple proxies, we can cross-check them to reduce the chances of getting it wrong.

So, back to that beach, and you standing on the shoreline, making up your mind. You might find you’re getting lightheaded, as there isn’t as much oxygen around as you’re used to – isotopic work on carbon and sulphur, as well as trace elements, suggest that the Ediacaran atmosphere contained relatively little oxygen, perhaps less than half of present atmospheric levels. It’s possible that the oxygen content of the air you’re breathing is roughly equivalent to that at the summit of Mount Everest in the present day, so you may struggle just to walk around.

The good news is, you probably aren’t being fried – sulphur isotope measurements tentatively suggest you’ve got a good ozone layer over your head by this point in Earth history (if you were contemplating a dip in the oceans of the Archaean, before 2.5 billion years ago, it’d be a different story – but the ammonia, hydrogen sulphide and methane-rich atmosphere would probably kill you long before the radiation did).

There is a large toolkit of proxies which tell us about conditions in the water, which is good news for your swim. Though pH proxies haven’t been widely applied this far back in time, there are some boron isotope studies  showing a pH of between 7 and 8.5, probably in a safe range for you, though marine organisms, especially calcified ones, may be more sensitive to pH changes. There’s also evidence from proxies such as  iron speciation that oxygenation was variable, so if you’re unlucky you might be heading for an unpleasant time in the water.

Title borrowed with apologies from Tom Lehrer’s song ‘Pollution‘.

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Where IS Everybody? A Tale of Rocks and Clocks

As with any pioneering effort – climbing Everest, reaching the South Pole, landing men on the moon – the innovations in the history of life are about what was done, who did it first, and how it affected the rest of the world.

The evolution of multicellular animals is one such innovation, and it’s a big one. If working with a selection of unicellular body plans is like having a box of different building bricks, then evolving multicellularity is suddenly realising that you can stick the bricks together to make something much bigger and more complicated.

Multicellularity had big repercussions for animal evolution and for palaeoenvironments too – animals are accomplished environmental engineers, disturbing sediment, building vast biological structures such as the Great Barrier Reef, and altering the distribution of nutrients and oxygen in their environments, with some very wide-ranging implications for the history of life on Earth. Some recent work suggests that the evolution of animals could even have enabled the widespread oxygenation of Earth’s atmosphere, a precondition for supporting many modern ecosystems.

Part of the genius of evolutionary trees is that they help us to predict what we might expect to see at particular moments in life’s history, and we can go on to test those predictions against the fossil record. The most primitive multicellular animals are sponges (Poriferans), meaning that the last common ancestor of sponges and the rest of the animal kingdom was most likely rather spongelike.

Because of that, Ediacaran palaeontologists are interested in finding out when sponges first evolved, and what the earliest sponges were like. The discovery that it was possible to use genetic sequences as a ‘clock’ gave a huge boost to this kind of research – now it was possible to predict when we might expect to see particular groups appearing.  However, there was a problem: as study after study placed the last ancestor of all animals at least 570 million years ago, meaning that the late Neoproterozoic should have been one big Poriferan party, the fossil record remained resolutely blank.  Where was everybody?

By Philcha (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or FAL], via Wikimedia Commons

A basic sponge body plan. By Philcha, via Wikimedia Commons

To answer that question, palaeontologists started to look more closely at the fossil record, hunting for sponges. Almost all sponges are built on a similar basic plan, made up of body walls composed of two layers of cells with a jellylike substance called the mesohyl between them. The body walls are porous, and sponges feed by wafting food-bearing water in through their body walls using tiny beating hairs called flagellae, and channelling it out along with their waste products through a gap in the body wall called the osculum. They have no nervous system, and no symmetry – both of those features evolved in later animal groups.  The problem is, most of this detail is preserved in cells, which generally don’t survive death and fossilisation.

It isn’t all doom and gloom though.  Many sponges build skeletons, but less helpfully they build them out of thousands of small pieces of silica called spicules, which readily scatter after death. So rather than looking for the fossils of entire sponges, palaeontologists are much more likely to find individual spicules. There are examples of spicules as old as 545 million years, though Ediacaran sponge spicules are often challenged on the grounds that they may not have been made by animals at all.

By Rob W. M. Van Soest, Nicole Boury-Esnault, Jean Vacelet, Martin Dohrmann, Dirk Erpenbeck, Nicole J. De Voogd, Nadiezhda Santodomingo, Bart Vanhoorne, Michelle Kelly, John N. A. Hooper [CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons

A variety of modern sponge spicules. By By Rob W. M. Van Soest et al., via Wikimedia Commons

There have also been some attempts to track the origin of sponges using chemicals called biomarkers. In principle, a biomarker is a substance which is only produced by a particular group of organisms – it has to be unique, and it has to be capable of being preserved unmistakably across large swathes of geological time. In 2009, the tongue-twisting molecule 24-isopropylcholestane was claimed as a biomarker for sponges, and was found in rocks older than 635 million years. This was interpreted to mean that there were abundant sponges around at that time, at least in some places. An interesting finding, and good news for molecular clocks, but the interpretation has been a source of controversy ever since. Palaeontologists, perhaps understandably, prefer to test their ideas with fossils.

The latest leap forward in this direction is a paper which came out last week, reporting on probably the most convincing sponge body fossil yet – a tiny, pinhead-sized fossil now named Eocyathispongia qiania, from the Doushantuo Formation in South China. Not only is this little fossil preserved right down to individual cells, but it is 600 million years old – falling neatly into that troubling gap between molecular clock predictions and the earliest known sponges in the fossil record.

Eocyathispongia qiania, newly described by Yin et al., 2015

Eocyathispongia qiania, a plausible early animal. From Yin et al., 2015.

So could Eocyathispongia qiania be one of those missing sponges? It’s certainly a good contender – the preservation of individual cells shows that it has the porous body walls of a conventional sponge, and what looks convincingly like a water flow system. It could be that the gulf between rocks and molecular clocks has just been bridged.

 

Further Reading:

Jonathan Antcliffe (2013), ‘Questioning the evidence of organic compounds called sponge biomarkers’Palaeontology 56, 5, 917-925.

Gordon D. Love, Emmanuelle Grosjean, Charlotte Stalvies, David A. Fike, John P. Grotzinger, Alexander S. Bradley, Amy E. Kelly, Maya Bhatia, William Meredith, Colin E. Snape, Samuel A. Bowring, Daniel J. Condon & Roger E. Summons (2009), ‘Fossil steroids record the appearance of Demospongiae during the Cryogenian period’Nature 457, 718-721.

Kevin J. Peterson, Jessica B. Lyons, Kristin S. Nowak, Carter M. Takacs, Matthew J. Wargo & Mark A. McPeek (2004), ‘Estimating metazoan divergence times with a molecular clock’, PNAS 101, 17, 6536-6541.

Zongjun Yin, Maoyan Zhu, Eric H. Davidson, David J. Bottjer, Fangchen Zhao & Paul Tafforeau (2015), ‘Sponge grade body fossil with cellular resolution dating 60 Myr before the Cambrian’PNAS doi:10.1073/pnas.1414577112

 

 

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Address to a Haggis Rock: Edinburgh’s GradSchool

A few weeks back, a Burns Night, a conference and a haggis hunt coincided on one excellent weekend. Here’s how it went:

Every year, the University of Edinburgh’s School of GeoSciences hosts GradSchool, a conference for its PhD students, where we get to present our work in the form of talks or posters. Unusually, the conference includes talks from a wide range of ‘Geo-‘ disciplines – if it’s happening in the school, it gets presented. This year’s conference was at the Peebles Hydro Hotel, on a snowy weekend near Burns Night.

Academic conferences can be funny things – time warps of talks, coffee breaks, talks, more coffee, posters and more talks. I’ve been to a few during the past couple of years, and at their best they leave me with replenished enthusiasm for my own work and for other people’s, and maybe with a few new ideas too. What’s impressive and unusual about GradSchool, though, is that it showcases research from both the ‘Sciences’ and ‘Humanities’ camps, which would otherwise seldom meet. So this years’ talks ranged from Mesozoic reptiles to dairy farming in Africa, North sea oil to detecting alien life, deep earth chemistry to forest ecology. First and third year PhD students usually give a talk, while second years present a poster. This year’s poster presentations took place in a room containing an enormous mural depicting the Battle of Bannockburn.

Poster presentations in the splendid Bannockburn Room.

Poster presentations competed for attention with scenes of massed battle.

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Palaeontologist and marine reptile nut Davide Foffa gets on the wrong side of some heavily armed cavalry in the Bannockburn Room.

Around all the talks and socialising, there was also time to go out and look at a couple of geological curiosities. This is where the haggis comes in – see, there’s a local rock in the borders of Scotland known as the Haggis Rock, and inspired perhaps by the Burns Night festivities, we decided to go out and find some.

The Haggis Rock outcrops widely in the Southern Uplands of Scotland, and we found some in a quarry a short drive from the hotel. As quarries go, I’ve seen worse, but it had its share of abandoned bathtubs and defunct kids’ toys. I’d love to tell you that the Haggis Rock is beautiful, splendid, a fine specimen of a rock, but to be honest, it looks rather a lot like this:

The Haggis Rock: Not an electrifying sight.

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Field trip leader Mark Wilkinson shows a young geologist some haggis rock.

At a glance, it’s tempting to conclude that the most interesting thing about the Haggis Rock is its name.  It’s inescapably grey, kind of gritty looking, and without many obvious features. However, look a little more carefully and the Haggis Rock begins to tell an interesting story. The Haggis Rock contains a variety of broken fragments of other rocks,  The  If you’re keen on the nitty-gritty of geological terms, then the Haggis Rock is a greywacke and a microconglomerate, meaning that it’s a mish-mash of small pieces of other rocks, transported and deposited with fine-grained sediment, then all lithified together. The fragments include a diverse range of sedimentary rocks, and, interestingly, small fragments of rocks more usually found in the upper mantle, deep in the Earth. So, how did they come to be washing about on the surface?

One common way for deep-earth rocks to end up at the surface is for them to be uplifted during mountain-building events, and that is exactly what happened here. During much of the Neoproterozoic and early Palaeozoic, southern Britain and Scotland were parts of two palaeocontinents, Laurentia and Baltica, separated by a wide ocean called Iapetus. They spent tens of millions of years steaming towards each other at a breakneck few millimetres per year. Around the 450 million year mark, they finally began to collide, crumpling Scotland and England to produce the Scottish southern uplands and the hills of northern England in a mountain-building event called the Caledonian Orogeny, which also rumpled rocks in mainland Europe.

Iapetus and the continents, 550 million years ago. Image from Wikipedia at http://commons.wikimedia.org/wiki/File:Positions_of_ancient_continents,_550_million_years_ago.jpg

Iapetus and continents, 550 million years ago. Image from Wikipedia.

One consequence of this is that the geology of Scotland and England vary considerably – after all, they had been apart for most of Earth’s history. Nineteenth-century palaeontologists spotted that the fossil assemblages in Scotland and England were dissimilar, with Scotland’s far more like that of North America, and southern Britain’s far more like that of the rest of Europe. However, it took over a century, and a historic paper by John Tuzo Wilson, to draw the story together with the emerging theory of plate tectonics, which at the time was just beginning to gain general acceptance.

It seems quite apt to me that our eclectic, interdisciplinary conference took place on the ground where two very different continents were brought into forceful collision, and contributed to one of the greatest paradigm shifts in 20th century science. The humanities and the sciences often don’t sit comfortably together, but when they do, research is the richer for it.

Thanks to the GradSchool committee for organising a fantastic conference, and to Mark Wilkinson for coming up with the idea of going to find Haggis Rock that close to Burns Night.

Further reading:

To read more about Iapetus and the geology of the Scottish borders:

Clarkson, E., and Upton, B.,  2010. Death of an Ocean: A Geological Borders Ballad, Dunedin Academic Press.

For a key paper in plate tectonics:

Wilson, J. Tuzo (13 August 1966). ‘Did the Atlantic close and then re-open?’ Nature 211 (5050): 676–681.

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Jurassic Lark: A Party at Port Mulgrave

Back in November I was invited to a housewarming weekend in Yorkshire by my college friends Steph and Phil. ‘Bring a sleeping bag and a towel’ said Steph, ‘and a hammer and chisel, if you have them’. Intrigued, I said I’d see what I could do.

Chigozie, Vito and Toby enter the ‘Its a Knockout’ phase of a fossil hunting trip.

By a happy coincidence, Steph and Phil had bought their first home right on top of a band of Jurassic rocks which sweeps up from Dorset and Devon on the southwest, all the way across England to the Yorkshire coast.  There are a number of different beaches on the Yorkshire coast where Jurassic rock can be got at, including Whitby and Robin Hood’s Bay. We chose Port Mulgrave on a cold, golden day, and stood looking over the crumbling grey cliffs before sliding all the muddy way down to the seashore.

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Port Mulgrave from the top of a hundred-metre mudslide down to the beach. Panorama by Adam Butler, subtly ruined by me.

During the Jurassic, England formed part of the supercontinent Pangaea, which was nearing the end of its 200-million-year lifespan and beginning to come apart at the seams. The area which would one day become England, which had previously been broiling away in the tropics, started its long journey northwards. At the same time, global sea levels were rising, submerging much of the land under warm seas which were home to large predatory reptiles like plesiosaurs and ichthyosaurs, but also to ancient oddities such as the ammonites and belemnites, which died, sank and turned that belt of Jurassic rock into one of the greatest treasuries of fossils anywhere in the British Isles. Some of the big names of nineteenth century palaeontology, such as William Buckland and Mary Anning, worked on the British Jurassic, and marine reptiles began to capture the public imagination rather as dinosaurs do today.

Duria_Antiquior

Duria Antiquior (Ancient Dorset) by Henry de la Beche. In which the Jurassic ocean is not an especially friendly place to be.

In Henry de la Beche’s reconstruction based on fossils from Dorset, the Jurassic oceans are crammed with various extinct nasties living a life of constant savagery. But Jurassic ecosystems were also coping with environmental pressures. The Jurassic started with one of the greatest mass extinctions in the history of life, which is thought to have killed off more than half of all species in a matter of tens of thousands of years. On land, the end-Triassic mass extinction removed many of the large animal species which had dominated during the Triassic, arguably clearing the way for the dinosaurs.

Caption

Dinosaur hunting, without success.

By the time the rock units at Port Mulgrave were deposited, sea levels were declining again, and at Mulgrave Bay we found plant fossils alongside the expected sea creatures. Port Mulgrave’s rocks are around 190 million years old (placing them in the Pliensbachian stage of the Jurassic period, all you stratigraphy fans out there). The Pliensbachian, incidentally, ended with its own episode of extinctions, sometimes called the Toarcian turnover. If you’re reading this and are ever after a good pun-based geology baking project (and you wouldn’t be the first), then I’d like to see that one.

Chigozie explores the Cleveland Ironstone Formation.

Having slithered down to the beach, we made a pretty good haul of fossils, mostly ammonites, belemnites and bivalves, as well as petrified wood and plant fragments, signs that this locality was probably relatively close to land. Port Mulgrave was the site of a mine for iron ore, and it’s clear why as soon as you get down to sea level – areas of rock and boulders are stained red with iron oxides leaching out of the rock and into the soil.

The rocks at Port Mulgrave form part of the Cleveland Ironstone Formation, and are divided into the (older) Penny Nab Member and the (younger) Kettleness Member. The whole lot is a mixture of shale and ironstone, and its high iron content made it the basis for a local economic boom during the Industrial Revolution, with County Durham coal providing the fuel for iron extraction. Teesside’s industrial towns owe their existence to Carboniferous coal forests and Jurassic ocean chemistry, a link acknowledged in Middlesbrough’s industrial nickname, ‘Ironopolis’.

Ironstone with nodules, some of which contain ammonites.

Ironstone and shale with nodules, some of which contain ammonites.

We collected loose rock from the foreshore, which included some nodules which, tapped open with a geological hammer, contained some gorgeously well-preserved ammonites. We mostly collected from the foreshore and picked up loose fossils from the shingle, and I ended up with a bag of water-worn ammonites to take back to Edinburgh and polish up. If they come out looking nice then I shall post some pictures here.

Ammonite from a loose iron nodule.

Belemnite a type of extinct, squid-like mollusc) with chisel for scale.

Thanks to Chigozie Nri, Toby Kirk, Joanna Shimmin, Vito Videtta, Ruth Laing and Phil Brown for being excellent company and staying on a windy beach hunting fossils for far longer than I would have thought possible, Adam Butler for letting me use his photo, and Steph Ward and Phil Maltas for organising a brilliant housewarming weekend.

Thanks everyone!

 

Further Reading

For tips on fossil collecting:

http://www.ukfossils.co.uk/guides.htm

For more on Port Mulgrave and Jurassic Yorkshire:

http://www.nationaltrust.org.uk/yorkshire-coast/history/view-page/item643807/

For a fascinating book on the geological history of Britain, and how bedrock geology influences our lives: The Hidden Landscape, by Richard Fortey

For more, and better, geological cake inspiration:

https://www.flickr.com/photos/geolsoc/sets/72157644551255832/

 

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Deep Time in Deep Water

Life in Deep Time has had a long holiday recently, during which I did a lot of writing and lab work, a few weeks of hiking and camping in various parts of the world, and several thousand miles of travel up and down the UK. If you’re a repeat reader of this blog, you’ll most likely be hearing about some of this in time. For now, though, a ‘what I did on my holidays’ piece from the deep, dark seas of the Ediacaran.

I ought to start with a confession: Despite having lived in Edinburgh for more than a year now, I haven’t been to Edinburgh Castle. It’s half an hour from my house, it’s one of Edinburgh’s most famous landmarks and it’s marvellously dramatic to look at, perched up there on its fortress-like mound of dolerite, yet I’ve never been in.

1024px-Edinburgh_Castle_from_Portsburgh (1)

Edinburgh Castle. A hundred metres of Carboniferous dolerite with a heavily armed Medieval guilt trip at the top. Image by Kim Traynor, via Wikimedia Commons.

In much the same way, I spent four years as an undergraduate in England, a couple of hours’ drive from Charnwood Forest in Leicestershire, one of the most important Ediacaran fossil localities in western Europe, and never went there – even though I was keen on palaeontology and on Ediacaran earth history particularly.

Well, one blustery day this summer, I finally made it, thanks to Alex Liu, Charlotte Kenchington and Breandán MacGabhann of Bristol, Cambridge and Edge Hill universities, who took the time to organise a field trip to Charnwood for a group of researchers – including PhD students – who work on the Ediacaran.

The Eye of Faith: Romain Guilbaud, Charlotte Kenchington and Breandan Macgabhann go foddil hunting.

Romain Guilbaud, Charlotte Kenchington and Breandán MacGabhann hunt for fossils on the Precambrian seafloor.

Charnwood’s fossils are over 560 million years old, placing them among the earliest macroscopic fossils in the fossil record, and the story of their discovery in 1957 is one of the classic tales of palaeontology. They are also, often, very beautiful – a collection of fronds and discs whose complexity belies the idea that everything alive in the Precambrian was sludgy and simple.

The frond-shaped fossils at Charnwood have a complex ‘fractal’ structure whereby one large frond is made up of units of other fronds which look just like it, which themselves are made up of more little fronds. They belong to a diverse assemblage of frond-shaped Ediacaran organisms called the rangeomorphs. The enormous surface areas that this kind of fractal structure creates mean that rangeomorphs could have been very good at absorbing oxygen and nutrients from the seawater around them, a feeding strategy called osmotrophy. However, we still aren’t sure exactly how they made a living.

These creatures turn out to have lived in the deep seas all over the world, and like many organisms in the Ediacaran, they are irresistibly odd.  They look rather like modern sea pens, which are relatives of sea anemones and jellyfish – a key Charnwood fossil, Charnia, is pictured next to a sea pen below, and I think you’ll agree there’s a resemblance.

Charnia, an Ediacaran rangeomorph (left) and

Charnia, an Ediacaran rangeomorph (left) and a modern sea pen (right). By Smith609 and Nick Hobgood, via Wikimedia Commons.

And yet, as so often, there’s a problem. More detailed work on Charnia and other rangeomorphs suggests that they grew from their tips, while sea pens grow from the base.  That makes it unlikely that they’re using the same growth mechanisms, and so they are probably not closely related. There’s even a school of thought that says they belong in an entirely different, extinct kingdom of life, the Vendobionta, whose construction was unlike anything in life’s history before or since.

It has to be said, though, that when you’re actually standing on the outcrop, in direct midday sunlight, these wonderful fossils can be hard to appreciate. Charnwood’s fossils were preserved under fine layers of volcanic ash, leaving them with only very shallow relief, so that they are almost invisible in the wrong light. Studying them in the field is so difficult that much of the work done on them is on casts, a strategy that has led to some spectacular results.  Here’s a bedding plane covered in hundreds of Ediacaran fossils. See them?

A beautifully preserved collection of Ediacaran fossils. If only I could see them!

Exactly.

One of my first encounters with this kind of fossil was walking into a lab and spending an afternoon with an anglepoise lamp trying to see something – anything – in the slabs of rock laid out on the benches. I felt as if I was being guided, blindfolded, round the Louvre, being told all about the wonders on display without actually being able to see them myself. With a bit of perseverance, though, and a lot of guidance from Alex and Charlotte, those elusive fronds and discs started to appear.

Disc and Frond

Eureka: Close up of a bedding plane showing a disc and frond.

Of course, another key part of the trip was the chance to meet other people working on the Precambrian for pints and a chat – which, as usual, ranged from in-depth discussion of research to swapping fieldwork anecdotes. Meeting other researchers who share your interests is always great, and it was a real, rare privilege to be shown round Charnwood and be able to see these famous fossils for myself.

Further Reading:

Antcliffe, J.B., and Brasier, M.D., 2007. ‘Charnia and sea pens are poles apart’, Journal of the Geological Society, London. 164, 49-51.

Brasier, M.D., Antcliffe, J.B., and Liu, A.G., 2012. ‘The Architecture of Ediacaran Fronds’, Palaeontology 55, 5, 1105-1124.

Hoyal Cuthill, J., and Conway Morris, S., 2014. ‘Fractal branching organisations of Ediacaran rangeomorph fronds reveal a lost Proterozoic body plan’, PNAS 111, 36, 13122-13126.

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