Anthropocene more an Event than an Epoch.

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 Newsletter 41, 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, USAErle 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 Great Anthropocene debate

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? GSA Today, 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 …

Human impact on surface geological processes

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.

Earliest sign of a sense of aesthetics

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 tools to 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.

Should you worry about being killed by a meteorite?

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.

Anthropocene edging closer to being ‘official’

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).

lignite
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’”

MOOCs: wheels come off the bandwagon

Massive open online courses (MOOCs for short) first mooted in 2006, surfaced with something of a pop in 2012. Intended to be open to all with Internet access, they promised a renaissance of higher education with the ’best’ professors, educational technologies and materials, flexibility, innovative assessment and accreditation (if chosen), no entry requirements, and very low cost at a time of relentlessly rising fees for conventional study. And they did not require attendance, although certificates of successful completion may be a currency for acceptance in conventional HE. They could be about literally anything at a variety of levels and involving a range of study times. By the end of 2016 MOOC programs had been set up by more than 700 universities worldwide, and around 58 million students had signed up to one of more courses. The general business model is described as ‘freemium’; i.e. a pricing strategy whereby a product or service is provided free of charge, with a premium charged for certification. There are innumerable variants of this model. The top providers are mainly consortia linking several universities and other academic and cultural entities. Futurelearn, although wholly owned by the formerly world-leading distance-learning distributor the British Open University, has 157 partners in Britain and globally. Its venture into the field involved its investing several tens of million UK pounds at start-up, which some believe was the source of its current financial difficulties.

The 11 January issue of Science published a brief account of the fortunes of a range of MOOC providers (Reich, J. & Ruipérez, J.A. 2019. The MOOC pivot. Science, v. 363, p. 130-131; DOI: 10.1126/science.aav7958) using data from edX that links Harvard University and MIT. The vast majority of learners who chose MOOCs never return after their first year. Growth in the market is concentrated almost entirely in affluent countries, whereas the model might seem tailor-made, and indeed vital, for less fortunate parts of the world. Completion rates are very low indeed, largely as a result of poor retention: since 2012 drop-out rates in the first year are greater than 80%. In the data used in the study both enrollments and certifications from 2012 to last year rose to peaks in the first three years (to 1.7 million and 50 thousand respectively) then fell sharply in the last two years (to <1 million and <20 thousand, respectively). Whatever the ‘mission’ of the providers  – was it altruistic or seeking a revenue stream? – the MOOC experience seems to be falling by the wayside. Perhaps many students took MOOCs for self-enlightenment rather than for a credential, as their defenders maintain. Well, the figures suggest that few saw fit to continue the experience. Surely, if knowledge was passed on at a level commensurate with participants requirements in a manner that enthused them, a great many would have signed up for ‘more of the same’: clearly that didn’t happen.

The authors conclude with, ‘Dramatic expansion of educational opportunities to underserved populations will require political movements that change the focus, funding, and purpose of higher education; they will not be achieved through new technologies alone.’

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