Many readers will have heard the vibration signal of an earthquake, as recorded by a seismometer, and replayed through a speaker: listen to some examples here. They are eerily like the sounds of falling, multi-storey buildings. Scary, especially if you think of the horrors of the devastation in SE Turkiye and NE Syria caused by the 6 February 2023 magnitude 7.8 event on the East Anatolian Fault system
Since P-waves are very like sound waves, audibly converting the one to the other is relatively simple. However, earthquakes are rarely single events, each major one being preceded by foreshocks and followed by aftershocks, both recurring over weeks or months. Highly active areas are characterised by earthquake swarms that can go on continuously, as happens with sea-floor spreading at mid-ocean ridges. In the case of Yellowstone National Park there are continual quakes, but there the seismicity results from magma rising and falling above a superplume. Most of such swarm-quakes are diminutive, so playing the speeded-up signal through a loudspeaker just sounds like a low, tremulous hiss.
Domenico Vicinanza a physicist at the Anglia Ruskin University in Cambridge UK specialises in creating music from complex scientific data, including those from CERN’s Large Hadron Collider in Geneva, to help interpret them. He has recently turned his hand to the Yellowstone earthquake swarm, converting the amplitudes and frequencies of its real-time seismograph to notes in a musical score: listen to the results here. They are surprisingly soothing, perhaps in the manner of the song of the humpback whale used by some to help with their chronic insomnia.
Most people are familiar with the term ‘blood diamonds’, meaning diamonds clandestinely exported from areas infested by the lethal activities of military and paramilitary forces. Indeed such conflicts are often fuelled by the large profits to be made from trading diamonds. One such source was in Sierra Leone during the civil war of 1991-2002. Others include Liberia, Côte d’ Ivoire, Angola and the Democratic Republic of Congo. Like illicit money, gemstones can be ‘laundered’ and find their way into conventional trade. To some extent the blood diamond trade has been slowed down by a programme of certification of packaged uncut diamond ‘rough’ by bona fide producers, and banning the sale of uncertified rough. The Kimberley Programme has been criticised because certificates can be issued in corrupt ways, so that blood diamonds probably still make their way to the international diamond markets: certification may hold no fears for those who force people to ine at gun point. However, because diamonds often show geochemical signatures and minute inclusions of other minerals that are unique to individual pipe-like intrusions of kimberlite that carry deep-mantle material to the surface. So, it is technically possible – but costly – to check for suspect rough. Such controls do not apply to other gemstones. A major source of very-high value gems is Myanmar (formerly Burma), whose widely condemned military dictatorship may be engaged in their unethical trade, including smuggling to neighbouring Thailand and China to avoid scrutiny.
Foot of bird chick preserved in Cretaceous amber from Kachin, Myanmar. Credit: Pinterest, Xing Lida, China University of Geosciences)
Myanmar is well endowed with sedimentary deposits that contain amber, the solidified resin from a variety of now extinct trees. Oddly, completely clear amber has low intrinsic value: it is semi-precious, albeit attractive. But it often contains inclusions of vegetation fragments, insects, feathers and small vertebrates, of interest to palaeontologists. Myanmar amber is especially interesting as it is dated to the Middle Cretaceous (~130 Ma), older than that found around the Baltic Sea (Eocene ~44 Ma), which was the main source for European jewellery since the 12th century, and that from Canada (Upper Cretaceous ~80 Ma). Myanmar amber has been used decoratively and medicinally in China since the 3rd century CE, and in Europe since prehistoric times. It is attractive but quite common, so historically amber never commanded high prices but was widely used as a trade item. Since the publicity attending the supposed extraction of dinosaur DNA from the bodies of reptile parasites to resurrect dinosaurs in Steven Spielberg’s 1993 film Jurassic Park, public and scientific interest in amber has boomed. It is primarily the exquisite preservation of encased organisms that piques the interest of palaeontologists. Papers that rely on the Myanmar amber have grown in number over the last ten years, despite the country being infamous for military repression of tribal and religious groups in its rural areas.
One of the most conflict-riven areas is the northern state of Kachin where the most interesting amber to palaeontologists is collected by the Kachin people of the Hukawng Valley. Government forces have been in conflict with the Kachin Independence Army since the 1960s, most particularly for control of the amber industry. A recent paper has focussed on the ethical issue of publications based on fossil-bearing amber from the area (Dunne, E.M. et al. 2022. Ethics, law, and politics in palaeontological research: The case of Myanmar amber. Communications Biology, v. 5, article no. 1023; DOI: 10.1038/s42003-022-03847-2).
In 2010 the military began forcibly to take over mines in Kachin. Between 2014 and 2021 the annual number of publication underwent a tenfold growth from between 10 to 15 to over 150, despite the fact that in 2015 the government in Yangon prohibited removal of fossils from the country. But the export laws exempt gemstones, so the growing demand for fossiliferous amber is clearly reflected in its supply to foreign scientists. Rare specimens that include vertebrate remains command prices up to US$100,000. The Myanmar amber trade is now estimated at around US$ 1 billion per annum. The Myanmar military took over all the mines in 2017, and is clearly the main supplier to palaeontologists.
In the seven-year period, only 3 papers out of 872 included contributors from Myanmar, which also suggests an element of ‘parachute science’: unsurprisingly Myanmar-based scientists also find it difficult to visit the Kachin area. Before 2014 most of the 69 publications involved scientists in the US; since then, the top spot has been occupied by Chinese scientists who have amassed 417. It seems clear that there is a web of contacts linking together the source of Myanmar amber, its market and science. In 2020 the Society of Vertebrate Paleontology called for a moratorium on publishing data from Kachin sources. But since then there is little sign that palaeontologists have taken any notice.
In November 2019 the Conservative government of Boris Johnson declared a moratorium on development of shale gas by hydraulic fracturing (‘fracking’) in England. This followed determined public protests at a number of potential fracking sites, the most intransigent being residents of Lancashire’s Fylde peninsula. They had been repeatedly disturbed since mid 2017 by low-magnitude earthquakes following drilling and hydraulic-fluid injection tests by Cuadrilla Resources near Little Plumpton village. Their views were confirmed in a scientific study by the British Geological Survey for the Oil and Gas Authority that warned of the impossibility of predicting the magnitude of future earthquakes that future fracking might trigger. The shale-gas industry of North America, largely in areas of low population and simple geology, confirmed the substantial seismic hazard of this technology by regular occurrences of earthquakes up to destructive magnitudes greater than 5.0. The Little Plumpton site was abandoned and sealed in February 2022.
Cuadrilla’s exploratory fracking site near Little Plumpton in Fylde, Lancashire. (Credit: BBC)
On 22 September 2022 the moratorium was rescinded by Jacob Rees-Mogg, Secretary of State for Business, Energy and Industrial Strategy in the new government of Liz Truss, two weeks after his appointment. This was despite the 2019 Conservative manifesto pledging not to lift the moratorium unless fracking was scientifically proven to be safe. His decision involved suggesting that the seismicity threshold for pausing fracking operations be lifted from magnitude 0.5 to 2.5, which Rees-Mogg claimed without any scientific justification to be ‘a perfectly routine natural phenomenon’. He further asserted that opposition to fracking was based around ‘hysteria’ and public ignorance of seismological science, and that some protestors had been funded by Vladimir Putin. In reality the Secretary of State’s decision was fuelled by the Russian Federation’s reducing gas supplies to Europe following its invasion of Ukraine, the soaring world price of natural gas and an attendant financial crisis. There was also a political need to be seen to be ‘doing something’, for which he has a meagre track record in the House of Commons. Rees Mogg claimed that lifting the moratorium would bolster British energy security. That view ignored the probable lead time of around 10 years before shale gas can become an established physical resource in England. Furthermore, an August 2018 assessment of the potential of UK shale-gas, by a team of geoscientists, including one from the British Geological Survey, suggested that shale-gas potential would amount to less than 10 years supply of UK needs: contrary to Rees-Mogg’s claim that England has ‘huge reserves of shale’. Indeed it does, but the vast bulk of these shales have no commercial gas potential.
Ironically, the former founder of Cuadrilla Resources, exploration geologist Chris Cornelius, and its former public affairs director, Mark Linder, questioned the move to unleash fracking in England, despite supporting shale-gas operations where geologically and economically appropriate. Their view is largely based on Britain’s highly complex geology that poses major technical and economic challenges to hydraulic fracturing. Globally, fracking has mainly been in vast areas of simple, ‘layer-cake’ geology. A glance at large-scale geological maps of British areas claimed to host shale-gas reserves reveals the dominance of hundreds of faults, large and small, formed since the hydrocarbon-rich shales were laid down. Despite being ancient, such faults are capable of being reactivated, especially when lubricated by introduction of fluids. Exactly where they go beneath the surface is unpredictable on the scales needed for precision drilling. Many of the problems encountered by Cuadrilla’s Fylde programme stemmed from such complexity. Over their 7 years of operation, hundreds of millions of pounds were expended without any commercial gas production. Each prospective site in Britain is similarly compartmentalised by faulting so that much the same problems would be encountered during attempts to develop them. By contrast the shales fracked profitably in the USA occur as horizontal sheets deep beneath entire states: entirely predictable for the drillers. In Britain, tens of thousands of wells would need to be drilled on a ‘compartment-by-compartment’ basis at a rate of hundreds each year to yield useful gas supplies. Fracking in England would therefore present unacceptable economic risks to potential investors. Cornelius and Linder have moved on to more achievable ventures in renewables such as geothermal heating in areas of simple British geology.
Jacob Rees-Mogg’s second-class degree in history from Oxford and his long connection with hedge-fund management seem not to be appropriate qualifications for making complex geoscientific decisions. Such a view is apparently held by several fellow Conservative MPs, one of whom suggested that Rees-Mogg should lead by example and make his North East Somerset constituency the ‘first to be fracked’, because it is underlain by potentially gas-yielding shales. The adjoining constituency, Wells, has several sites with shale-gas licences but none have been sought within North East Somerset. Interestingly, successive Conservative governments since 2015, mindful of a ‘not-in-my-backyard’ attitude in the party’s many rural constituencies, have placed a de-facto ban on development of onshore wind power.
I don’t often review books on Earth-logs, but one that is pending publication may interest readers (Ian Francis, Stuart Holmes and Bruce Yardley 2022. The Lake District: Landscape and Geology. Marlborough: The Crowbrook Press; ISBN: 078 0 7198 4011 1). Ian Francis urged me to create Earth Pages, the predecessor to Earth-logs. One good turn deserves another, but this is a very good book. Unlike nearly all area-specific geoscientific books it is not primarily a guidebook. Instead it uses the internationally famous Lake District as a means of teaching how to fathom what a landscape represents. In this case, one with a history going back half a billion years, involving closure of an ocean, destruction of a mountain chain and sediment deposition in a ‘shallow, inland sea’. The last couple of million years or so of cycles of glaciation and river erosion have sculpted its present form. Finally, it became the home range of human hunter gatherers, once the ice had melted away around 10 thousand years ago. Britain’s first stone-age tillers and herders colonised its lower elevations, followed by miners and metal smelters, Roman, Viking and Anglo Saxon invaders and settlers. Its beauty and complexity have inspired poets and artists, and they in turn have drawn in more visitors per km2 than perhaps any other National Park on Earth, and far more per annum than its indigenous population.
Cover of The Lake District: Landscape and Geology
Ian, Stuart and Bruce lace their book with some of the best landscape images of the Lake District that I have come across, which invite you to read the text. The Lake District is pitched at a level that anyone can understand, with a minimum of jargon and a pleasant style. Basic geological concepts are covered in separate ‘boxes’, where the main thread requires them and for those who want a little more science. Geology being an observational science, there is some emphasis on indicators of natural processes, such as elliptical drumlins whose sculpting by flowing ice aligns their long axes, and exotic boulders made of rocks only present miles away whose presence suggests the source of the ice that had moved them. Solid rock outcrops in the Lakes are products of many Earth processes, both internal and at the former surface. There are granitic rocks that intruded through once volcanic and sedimentary rocks. Their internal features tell the rocktypes apart, such as the layering of sediments, often cleaved and folded by deformation. and the lack of structure in granite that cuts the layering, yet imparts new minerals to the older marine rocks as a result of igneous heating to very high temperatures.
Most of the geological concepts raised in the main text are amplified by narratives of seven field trips; provided the reader physically walks through them. And why shouldn’t they? Each of them involves only a few kilometres of gentle walking from parking spaces on metalled roads. They cover all the solid geology, from the regionally oldest rocks, the Early-Ordovician, deep-water Skiddaw Slates; upwards in geological time through the varied products of later Ordovician volcanism and marine sediments; the thick Silurian mudstones and silts; and the youngest and structurally simplest shallow-marine Carboniferous limestone. The sediments all contain fossils and the volcanics are full of evidence of the environment onto which they poured – an oceanic island arc. A simple story is unveiled by all, such as following a track on the flanks of Blencathra, a hill in the Northern Fells. From slates with cleavage formed by compressive forces acting on muds; to a point where new minerals have grown in them through later heating; then to where heat was so intense that the slates came to resemble igneous rocks; and finally outcrops of a granite whose much later intrusion as magma explains the simple sequence. All the trips are like that: not too much to take in, but enough to hammer home the various rudiments of geology.
Britain was where the modern Earth sciences were largely forged. But that was in the absence of complete exposure of all the solid rock that underpins it. What lies between outcrops is the modern natural world and a diversity of ecosystems to which The Lake District also draws attention. Even professional geologists get bored to tears by trudging unendingly over nothing but rock. They enjoy flowers, trees, birds, streams and tarns with fish as a relief. Some of the text also taught me about oddities created by Cumbrian farmers: bields, which are shelters for shepherds and sheep; washfolds where sheep used to be gathered and cleaned prior to shearing, and lots more about the unique upland farming culture of Cumbria. I hope the book proves physically durable, for it will surely find its way into secondary-school and first-year undergraduate field trips. It is also ideal for any family aiming at a fortnight’s holiday in the Lakes, but wondering what to do. The book will get well-thumbed and wet – the one drawback of the Lake District is its annual rainfall, averaging 3.3 metres! Go in April, May or early June to escape the worst of it and that of tourists, and to see its ecology at its best. I’m giving my complimentary copy to my grandchildren, because I get annoyed when they complain of boredom!
The Vattenfall lignite mine in Germany; the Anthropocene personified
The issue of whether or not to assign the time span during which human activities have been significantly affecting the planet and its interwoven Earth Systems has been dragging on since the term ‘Anthropocene’ was first proposed more than two decades ago. A suggestion that may resolve matters, both amicably and with a degree of scientific sense, has emerged in a short letter to the major scientific journal Nature, written by six eminent scientists (Bauer, A.M. et al. 2021. Anthropocene: event or epoch? Nature, v. 597, p. 332; DOI: 10.1038/d41586-021-02448-z). The full text is below
“The concept of the Anthropocene has inspired more than two decades of constructive scholarship and public discussion. Yet much of this work seems to us incompatible with the proposal to define the Anthropocene as an epoch or series in the geological timescale, with a precise start date and stratigraphic boundary in the mid-twentieth century. As geologists, archaeologists, environmental scientists and geographers, we have another approach to suggest: recognize the Anthropocene as an ongoing geological event.
The problems with demarcating the Anthropocene as a globally synchronous change in human–environment relations, occurring in 1950 or otherwise, have long been evident (P. J. Crutzen and E. F. Stoermer IGBP Newsletter41, 17–18; 2000). As an ongoing geological event, it would be analogous to other major transformative events, such as the Great Oxidation Event (starting around 2.4 billion years ago) or the Great Ordovician Biodiversification Event (around 500 million years ago).
Unlike formally defined epochs or series, geological events can encompass spatial and temporal heterogeneity and the diverse processes — environmental and now social — that interact to produce global environmental changes. Defining the Anthropocene in this way would, in our view, better engage with how the term has been used and criticized across the scholarly world.”
AUTHORS: Andrew M. Bauer, Stanford University, Stanford, California, USA; Matthew Edgeworth, University of Leicester, Leicester, UK; Lucy E. Edwards, Florence Bascom Geoscience Center, Reston, Virginia, USA; Erle C. Ellis, University of Maryland, Baltimore County, Maryland, USA ; Philip Gibbard, Scott Polar Research Institute, University of Cambridge, Cambridge, UK; Dorothy J. Merritts, Franklin and Marshall College, Lancaster, Pennsylvania, USA.
I have been grousing about the attempt to assign Epoch/Series status to the Anthropocene for quite a while (you can follow the development of my personal opinions by entering ‘Anthropocene’ in the Search Earth-logs box). In general I believe that the proposal being debated is scientifically absurd, and a mere justification for getting a political banner to wave. What the six authors of this letter propose seems eminently sensible. I hope it is accepted by International Commission on Stratigraphy as a solution to the increasingly sterile discussions that continue to wash to and fro in our community. Then perhaps the focus can be on action rather than propaganda.
As things have stood since 21 May 2019, a proposal to accept the Anthropocene as a formal chrono-stratigraphic unit defined by a GSSP at its base around the middle of the 20th century is before the ICS and the International Union of Geological Sciences (IUGS) for ratification. It was accepted by 88% of the 34-strong Anthropocene Working Group of the ICS Subcommission on Quaternary Stratigraphy. But that proposal has yet to be ratified by either the ICS or IUGS. Interestingly, one of the main Anthropocene proponents was recently replaced as chair of the Working Group.
The Bagger 288 bucket wheel reclaimer moves from one lignite mine to another in Germany: an apt expression of modern times
Followers of Earth-logs and its predecessor, should be familiar with the concept of ‘The Anthropocene’. More recent readers can hardly have escaped it, for it has become a recurrent motif that extends far beyond science to the media, the social sciences and even the arts. Some circles among the ‘chattering classes’ speak of little else. It has become a trope – a word with figurative or metaphorical meaning. In 2000, atmospheric chemist and Nobel Laureate Paul Crutzen suggested that the increasingly clear evidence that human society is having growing impacts on the Earth system should be recognised by a new stratigraphic Epoch. Some Fellows of the Geological Society of London launched an attempt to formalise the suggestion through the society’s Stratigraphic Commission (Zalasiewicz, J. and 20 others 2008. Are we now living in the Anthropocene?GSAToday, v.18(ii), p. 4-8; DOI: 10.1130/GSAT01802A.1). In 2009 Jan Zalasiewicz of the University of Leicester became the first chair of the Anthropocene Working Group (AWG) within the International Commission on Stratigraphy (ICS). A dozen years on, stratigraphers continue to debate the Anthropocene (See: Brazil, R. 2021. Marking the Anthropocene. Chemistry World, 29 January 2021). One of the problems facing its supporters is the lack of agreement about what it is and when it started.
Since 1977 the ICS has been searching for localities, known as Global Boundary Stratotype Sections and Points, or GSSPs, that mark the actual beginning of each basic division of the geological record: Eons, Eras, Periods, Epochs and Ages. So far, those for Epochs and longer divisions have been agreed and GSSP markers have been cemented in place, sometimes with quite large monuments, if not actual golden spikes. Those for the shortest timespans – Ages – are proving more difficult to agree on. These GSSPs have to have global significance, yet the very nature of stratigraphy means that a fair number of the most brief rock sequences revealed by field work either formed at different times across the globe, or there is no incontrovertible dating method to record their beginning and end.
Currently, we live in the Holocene Epoch whose beginning marked the global climate system’s exit from the frigid Younger Dryas at 11.7 ka ago. The Holocene (‘entirely recent’) Epoch marks the latest interglacial. When it began every human being was Homo sapiens, made a living as a hunter-gatherer and eventually expanded into every ecosystem that offered sustenance on all continents bar Antarctica. Within a few thousand years some began sedentary life as farmers and herders after their domestication of a range of plant and animal species. A few millennia later agriculture had a growing foothold everywhere except in Australia. Natural tree cover began to be cleared and organised grazing steadily changed other kinds of ecosystem. Human influences, other than scattered artefacts and bones, became detectable in geological formations such as lake-bed sediments and peat mires. The geological record of the Holocene is by no means consistent globally, there being lots of gaps. That is partly because sedimentary systems continually deposited, eroded and transported sediments on the landmasses. In the tropics and much of the Southern Hemisphere the Younger Dryas is, in any case, barely recognisable in post-Ice Age deposits, so the start of the Holocene there is vague. Things are simpler on the deep sea floor, as muds accumulate with no interruption. But it was only when data became available from drill cores through continental ice masses on Antarctica, Greenland and scattered high mountains that any detailed sense of changes and their pace emerged. The major climatic perturbation of the Younger Dryas and its end only became clear from the undisturbed annual layering in Greenland ice cores. It proved to have been extremely fast: a couple of decades at most. The GSSP for the start of the Holocene therefore lies in a single Greenland ice core preserved by cold storage in Copenhagen. It is a somewhat ephemeral record.
Leaving aside for the moment that the Anthropocene adds the future to the geological record, when was it supposed to start? Its name demands that it be linked to some human act that began to change the world. That is implicit in the beginning of agriculture which held out the prospect of continuous growth in human populations by securing food resources rather than having to seek them. But such an event is not so good from the standpoint of purist stratigraphy as it happened at different times at different places and probably for different reasons (See: Mithen, S. 2004. After the Ice: A Global Human History, 20,000 – 5000 BC. Weidenfeld and Nicolson, London; ISBN-13: 978-0753813928 [A superb read]). A case has been made for the European conquest and colonisation of the Americas which was eventually followed by the death from European diseases of tens of millions of native people, many of whom were farmers in the Amazon basin. The Greenland ice records a decline in atmospheric CO2 between 1570 to 1620 CE, which has been ascribed to massive regrowth of previously cleared tropical rainforest. That would define a start for the Anthropocene at around 1610 CE. Yet the main driver for erecting an Anthropocene Epoch is global warming, which has grown exponentially with the burning of fossil fuels and CO2 emissions since the ill-defined start of the Industrial Revolution (late 18th – early 19th century). It looks like in a year or so the ICS is due to debate a much later start at the peak of nuclear weapon fallout in 1964, which its champions claim to coincide with the ‘Great Acceleration’ in world economic growth, emissions and warming.
If that is accepted, anyone still alive who was born before 1964 is a relic of the Holocene, as Philip Gibbard secretary-general of ICS wryly observed, whereas our children and grandchildren will be wholly of the Anthropocene. We Holocene relics only grasped the change at the start of the 21st century! The very nature of exponential growth is that its tangible effects always come as a surprise. The build-up of human influence on the world has been proceeding stealthily since not long after the Holocene began. Annoyingly, the very name Anthropocene lays the blame on the whole of humanity. In reality it is an outcome of a mode of economy that demands continual exponential growth. That mode – the World Economy – lies completely beyond the reach of social and political control. It is effectively inhuman. So, why the pessimism – can’t human beings get rid of an ethos that is obviously alien to their interests? Perhaps ‘Anthropocene’ might be an apt name for the aftermath of such a reckoning, which may last long enough to be properly regarded as an Epoch …
I last wrote about sedimentation during the ‘Anthropocene’ a year ago (See: Sedimentary deposits of the ‘Anthropocene’, November 2019). Human impact in that context is staggeringly huge: annually we shift 57 billion tonnes of rock and soil, equivalent to six times the mass of the UKs largest mountain, Ben Nevis. All the world’s rivers combined move about 35 billion tonnes less. I don’t particularly care for erecting a new Epoch in the Stratigraphic Column, and even less about when the ‘Anthropocene’ is supposed to have started. The proposal continues to be debated 12 years after it was first suggested to the IUGS International Commission on Stratigraphy. I suppose I am a bit ‘old fashioned’, but the proposals is for a stratigraphic entity that is vastly shorter than the smallest globally significant subdivision of geological time (an Age) and the duration of most of the recorded mass extinctions, which are signified by horizontal lines in the Column. By way of illustration, the thick, extensive bed of Carboniferous sandstone on which I live is one of many deposited in the early part of the Namurian Age (between 328 and 318 Ma). Nonetheless, anthropogenic sediments of, say, the last 200 years are definitely substantial. A measure of just how substantial is provided by a paper published online this week (Kemp, S.B. et al. 2020. The human impact on North American erosion, sediment transfer, and storage in a geologic context. Nature Communications, v. 11, article 6012; DOI: 10.1038/s41467-020-19744-3).
‘Badlands’ formed by accelerated soil erosion.
Anthropogenic erosion, sediment transfer and deposition in North America kicked off with its colonisation by European immigrants since the early 16th century. First Americans were hunter-gatherers and subsistence farmers and left virtually no traces in the landscape, other than their artefacts and, in the case of farmers, their dwellings. Kemp and colleagues have focussed on late-Pleistocene alluvial sediment, accumulation of which seems to have been pretty stable for 40 ka. Since colonisation began the rate has increased to, at present, ten times that previously stable rate, mainly during the last 200 years of accelerated spread of farmland. This is dominated by outcomes of two agricultural practices – ploughing and deforestation. Breaking of the complex and ancient prairie soils, formerly held together by deep, dense mats of grass root systems, made even flat surfaces highly prone to soil erosion, demonstrated by the ‘dust bowl’ conditions of the Great Depression during the 1930s. In more rugged relief, deforestation made slopes more likely to fail through landslides and other mass movements. Damming of streams and rivers for irrigation or, its opposite, to drain wetlands resulted in alterations to the channels themselves and their flow regimes. Consequently, older alluvium succumbed to bank erosion. Increased deposition behind an explosion of mill dams and changed flow regimes in the reaches of streams below them had effects disproportionate to the size of the dams (see: Watermills and meanders, March 2008). Stream flow beforehand was slower and flooding more balanced than it has been over the last few hundred years. Increased flooding, the building of ever larger flood defences and an increase in flood magnitude, duration and extent when defences were breached form a vicious circle that quickly transformed the lower reaches of the largest American river basins.
North American rates of alluvium deposition since 40 Ka ago – the time axis is logarithmic. (Credit: Kemp et al., 2020; Fig. 2)
All this deserves documentation and quantification, which Kemp et al. have attempted at 400 alluvial study sites across the continent, measuring >4700 rates of sediment accumulation at various times during the past 40 thousand years. Such deposition serves roughly as a proxy for erosion rate, but that is a function of multiple factors, such as run-off of rain- and snow-melt water, anthropogenic changes to drainage courses and to slope stability. The scale of post-settlement sedimentation is not the same across the whole continent. In some areas, such as southern California, the rate over the last 200 years is lower than the estimated natural, pre-settlement rate: this example may be due to increased capture of surface water for irrigation of a semi-arid area so that erosion and transport were retarded. In others it seems to be unchanged, probably for a whole variety of reason. The highest rates are in the main areas of rain-fed agriculture of the mid-west of the US and western Canada.
In a nutshell, during the last century the North American capitalism shifted as much sediment as would be moved naturally in between 700 to 3000 years. No such investigation has been attempted in other parts of the world that have histories of intense agriculture going back several thousand years, such as the plains of China, northern India and Mesopotamia, the lower Nile valley, the great plateau of the Ethiopian Highlands, and Europe. This is a global problem and despite its continent-wide scope the study by Kemp et al. barely scratches the surface. Despite earnest endeavours to reduce soil erosion in the US and a few other areas, it does seem as if the damage has been done and is irreversible.
Maybe because of the Covid-19 pandemic, there has been a dearth of interesting new developments in the geosciences over that last few months: the ‘bread and butter’ of Earth-logs. So instead of allowing a gap in articles to develop, and as a sign that I haven’t succumbed, this piece concerns one of the most intriguing discoveries in palaeoanthropology. In 1925 Wilfred Eitzman, a school teacher, investigated a cave in the Makapansgat Valley in Limpopo Province, South Africa that had been exposed by quarry workers. His most striking discovery was a polished pebble made of very fine-grained, iron-rich silica, probably from a Precambrian banded iron formation. Being round and deeply pitted, it had clearly been subject to prolonged rolling and sand blasting in running water and wind. Eerily, whichever way it was viewed it bore a striking resemblance to a primate face: eyes, mouth, nose and, viewed from the rear, a disturbing, toothless grin. We have all picked up odd-looking pebbles on beaches or a river bank: I recently found a sandstone demon-cat (it even has pointy ears) when digging a new vegetable patch.
The Makapansgat Pebble. Inverted it still resembles a face and its obverse side does too.
What is different about the Makapansgat Pebble is that Eitzman found it in a cave-floor layer full of bones, including those of australopithecines. The cave is located in dolomitic limestone outcrops high in the local drainage system, so it’s unlikely that the pebble was washed into it. The nearest occurrence of banded iron formation is about 20 kilometres away, so something must have carried the pebble for a day or more to the cave. The local area has since yielded a superb palaeontological record of early hominin evolution, stimulated by Eitzman’s finds. He gave the fossils and the pebble to Raymond Dart, the pioneer of South African palaeoanthropology. Dart named the hominin fossils Australopithecus prometheus because associated bones of other animals were covered in black stains that Dart eagerly regarded as signs of burning and thus cooking. When it became clear that the stains were of manganese oxide the name was changed to Au. africanus, the fossils eventually being dated to around 3 million years ago.
Dart was notorious for his showmanship, and the fossils and the Makapansgat Pebble ‘did the rounds’ and continue to do so. In 2016 the pebble was displayed with a golden rhino, a collection of apartheid-era badges and much more in the British Museum’s South Africa: the art of a nation exhibition. Well, is the pebble art? As it shows no evidence of deliberate working it can not be considered art, but could be termed an objet trouvé. That is, an ‘object found by chance and held to have aesthetic value to an artist’. The pebble’s original finder 3 million years ago must have found the 0.25 kg pebble sufficiently interesting to have carried it back to the cave, presumably because of its clear resemblance to a hominin head: in fact a multiple-faced head. Was it carried by a cave-dwelling australopithecine or an early member of genus Homo who left no other trace at Makapansgat? At an even earlier time a so-far undiscovered hominin did indeed make simple stone toolsto dismember joints of meat on the shores of Lake Turkana in Kenya. It is impossible to know who for sure carried the pebble, nor to know why. Yet all living primates are curious creatures, so it is far from impossible that any member of the hominins in our line of descent would have collected portable curiosities.
In 1994 Clark Chapman of the Planetary Science Institute in Arizona and David Morrison of NASA’s Ames Research Center in California published a paper that examined the statistical hazard of death by unnatural causes in the United States (Chapman, C. & Morrison, D. 1994. Impacts on the Earth by asteroids and comets: assessing the hazard. Nature, v. 367, p. 33–40; DOI:10.1038/367033a0). Specifically, they tried to place the risk of an individual being killed by a large asteroid (~2 km across) hitting the Earth in the context of more familiar unwelcome causes. Based on the then available data about near-Earth objects – those whose orbits around the Sun cross that of the Earth – they assessed the chances as ranging between 1 in 3,000 and 1 in 250,000; a chance of 1 in 20,000 being the most likely. The results from their complex calculations turned out to be pretty scary, though not as bad as dying in a car wreck, being murdered, burnt to death or accidentally shot. Asteroid-risk is about the same as electrocution, at the higher-risk end, but significantly higher than many other causes with which the American public are, unfortunately, familiar: air crash; flood; tornado and snake bite. The lowest asteroid-risk (1 in 250 thousand) is greater than death from fireworks, botulism or trichloroethylene in drinking water; the last being 1 in 10 million.
Chapman and Morrison cautioned against mass panic on a greater scale than Orson Welles’s 1938 CBS radio production of H.G. Wells’s War of the Worlds allegedly resulted in. Asteroid and comet impacts are events likely to kill between 5,000 and several hundred million people each time they happen but they occur infrequently. Catastrophes at the low end, such as the 1908 Tunguska air burst over an uninhabited area in Siberia, are likely to happen once in a thousand years. At the high end, mass extinction impacts may occur once every hundred million years. As might be said by an Australian, ‘No worries, mate’! But you never know…
Michelle Knapp’s Chevrolet Malibu the morning after a stony-iron mmeteorite struck it. Bought for US$ 300, Michelle sold the car for US$ 25,000 and the meteorite fetched US$ 50,000 (credit: John Bortle)
How about ordinary meteorites that come in their thousands, especially when the Earth’s orbit takes it through the former paths taken by disintegrating comets? When I was a kid rumours spread that a motor cyclist had a narrow escape on the flatlands around Kingston-upon-Hull in East Yorkshire, when a meteorite landed in his sidecar: probably apocryphal. But Michelle Knapp of Peeskill, New York, USA had a job for the body shop when a 12 kg extraterrestrial object hit her Chevrolet Malibu, while it was parked in the driveway. In 1954, Ann Hodges of Sylacauga, Alabama was less fortunate during an afternoon nap on her sofa, when a 4 kg chondritic meteorite crashed through her house roof, hit a radiogram and bounced to smash into her upper thigh, badly bruising her. For an object that probably entered the atmosphere at about 15 km s-1, that was indeed a piece of good luck resulting from air’s viscous drag, the roof impact and energy lost to her radiogram. The offending projectile became a doorstop in the Hodge residence, before the family kindly donated it to the Alabama Museum of Natural History. Another fragment of the same meteorite, found in a field a few kilometres away, fetched US$ 728 per gram at Christie’s auction house in 2017. Perhaps the most unlucky man of the 21st century was an Indian bus driver who was killed by debris ejected when a meteorite struck the dirt track on which he was driving in Tamil Nadu in 2016 – three passengers were also injured. Even that is disputed, some claiming that the cause was an explosive device.
The issue of erecting a new stratigraphic Epoch encompassing the time since humans had a global effect on the Earth System has irked me ever since the term emerged for discussion and resolution by the scientific community in 2000. An Epoch in a chronostratigraphic sense is one of several arbitrary units that encompass all the rocks formed during a defined interval of time. The last 541 million years (Ma) of geological time is defined as an Eon – the Phanerozoic. In turn that comprises three Eras – Palaeozoic, Mesozoic and Cenozoic. The third level of division is that of Periods, of which there are 11 that make up the Phanerozoic. In turn the Periods comprise a total of 38 fourth-level Epochs and 85 at the fifth tier of Ages. All of these are of global significance, and there are even finer local divisions that do not appear on the International Chronostratigraphic Chart . If you examine the Chart you will find that no currently agreed Epoch lasted less than 11.7 thousand years (the Holocene) and all the others spanned 1 Ma to tens of Ma (averaged at 14.2 Ma). Indeed, even Ages span a range from hundreds of thousands to millions of years (averaged at 6 Ma).
The Vattenfall lignite mine in Germany; the Anthropocene personified
In the 3rd week of May 2019 the 34-member Anthropocene Working Group (AWG) of the International Commission on Stratigraphy (ICS) sat down to decide on when the Anthropocene actually started. That date would be passed on up the hierarchy of the geoscientific community eventually to meet the scrutiny of its highest body, the executive committee of the International Union of Geological Sciences, and either be ratified or not. In the meantime the AWG is seeking a site at which the lower boundary of the Anthropocene would be defined by the science’s equivalent of a ‘golden spike’; the Global boundary Stratotype Section and Point (GSSP). Continue reading “Anthropocene edging closer to being ‘official’”→
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