Since it was coined in the year 2000 by Paul Crutzen and Eugene Stoermer, the term “Anthropocene” has taken the world by storm – pretty much in the same way as the phenomenon it describes. Humanity’s impact on the planet has become so all-encompassing that it warrants giving this period a new name. As a colloquial term that is all snazzy, but are we actually leaving a tangible trace in the rock record to signal a transition to a new period?

The Anthropocene as a Geological Time Unit: A Guide to the Scientific Evidence and Current Debate, edited by Jan Zalasiewicz, Colin N Waters, Mark Williams, and Colin Peter Summerhayes, published by Cambridge University Press in March 2019 (hardback, 361 pages)

Several authors have already written thought experiments to try and answer this question. But the real answer lies in the realm of stratigraphy, the geological subdiscipline that studies rock layers. As with many other conventions, to ensure scientists around the globe all talk about the same thing and use the same names, there is an official body for that. The International Commission on Stratigraphy (ICS) formally decides on naming and dating of geological periods and maintains the International Chronostratigraphic Chart, better known as the Geological Time Scale (find a PDF here).

Formal acceptance of a new name means clearing a raft of bureaucratic and academic hurdles first. So, in 2009, the editors of the current book got together to form the Anthropocene Working Group to start preparing a formal submission to, ultimately, the ICS. Two large publications, a special issue of The Philosophical Transactions of the Royal Society A and A Stratigraphical Basis for the Anthropocene, came first. Now this edited collection does what it says on the tin, providing the latest update on the evidence and the debate by summarizing a huge body of work.

The first chapter provides a short history of what I have sketched above and, for the reader not versed in stratigraphy, useful basic information on how stratigraphy works, past decisions on defining and naming geological periods, plus a very interesting and relevant section outlining why formal acceptance and definition of the Anthropocene matters. The bulk of the book consists of five chapters examining how humans have tangibly modified our planet, and whether this leaves stratigraphically suitable markers. Depending on your viewpoint, this could be taken as a catalogue of our atrocities or a celebration of our achievements.

“The bulk of the book […] examines how humans have tangibly modified our planet, and whether this leaves stratigraphically suitable markers. Depending on your viewpoint, this could be taken as a catalogue of our atrocities or a celebration of our achievements.”

The range of impacts covered is comprehensive and includes some eye-opening facts and frighteningly large numbers. We are leaving a stratigraphical legacy by changing natural patterns of sedimentation via erosion and river damming. We construct infrastructure and buildings above and below ground and create many novel types of “rocks” such as cement, asphalt, and concrete (so much so that we risk running out of suitable sand). But we also enrich soils and sediments with fly-ash and soot from burning fossil fuels. And this is before we even talk of the insane amounts of plastics that end up in our environment, now degrading into micro- and nanoplastics that are found everywhere. And then there are what Zalaziewicz and others have dubbed “technofossils”: all the objects that we discard in refuse tips, revealing a stratigraphy all of their own.

Less visible but no less influential are chemostratigraphical changes. That is to say, the release of carbon and methane from (again) fossil fuel burning, nitrogen and phosphorus from synthetic fertilisers, sulfur compounds, metals, organic (in the chemical sense) compounds such as pesticides and fire retardants (your POPs, PAHs, PCBs, PBDEs, etc.) and, lest we forget, radionuclides from atomic and hydrogen bombs. All these have left detectable accumulations in air, water (including ice), and soil. A biostratigraphical signature is detectable as both recent and ongoing extinctions (particularly the extinction of the Quaternary megafauna, though see my review of End of the Megafauna), the rapid spread of invasive species and domestic animals (with broiler chickens being one example of an expected future signal in the fossil record), and the fate of coral reefs. Finally, there is climate change, made visible in changes to ice cover and sea level.

“And then there are […] “technofossils”: all the objects that we discard in refuse tips, revealing a stratigraphy all of their own.”

What I casually summarise here in two paragraphs is presented in-depth, providing an overview of a huge body of research. And despite subchapters being contributed by many different authors, the overall flow and coherence of the text are good. Although not the first book to detail humanity’s planetary impact, the question of interest here is which of these would make suitable stratigraphic markers.

So what makes a good marker? Ideally one that is global in extent and that was laid down synchronously, i.e. very rapidly, so that the age of the marker is the same wherever measured. A volcanic ash layer is a good example, and so, of course, is the iridium spike signalling the meteorite impact at the K-Pg boundary.

Not all of the potential markers discussed in this book meet these criteria, even though they reveal humanity’s impact. So, the sudden appearance of so many new long-lasting rock-like compounds and plastics is a good marker. Another one is lead released during the burning of fossil fuels, which shows up in natural archives such as sediments, peat mires, and ice cores. (Plus, there is a precedent here: Greenland ice cores show a lead spike at the height of Greek-Phoenician and Roman mining). But the appearance of soils modified by human agriculture is an example of a signal that is too localised and too diachronous (the opposite of synchronous) to be of use. The same is true for the occurrence of stone tools, though modern technofossils such as broken iPhones could be useful.

“When did the Anthropocene start? A consensus is forming on the 1950s. This is when human population size boomed and many things basically went into overdrive “

A similar question is the when. Though some scientists favour the rise of agriculture ~10,000 years ago or the beginning of the Industrial Revolution in the late 1700s as the start of the Anthropocene, the editors here outline how a consensus is forming on the 1950s. This is when human population size boomed and many things basically went into overdrive. When plotted on graphs, many indicators considered here show a sharp upward inflexion right around this time.

As with other periods, it is highly likely that a combination of proxy signals will have to be used to define the Anthropocene – many natural archives are either sensitive to disturbance (lake sediments vs. burrowing animals), or record signals with a delay (e.g. isotope signals in stalagmites). For the moment this is all work in progress, and a formal submission to the ICS is still being prepared by the Anthropocene Working Group. Much like the closely-allied Intergovernmental Panel on Climate Change reports are the go-to books on climate change (also published by Cambridge University Press), this book is the most definitive and up-to-date reference work for anyone working on or interested in the geological case for the Anthropocene.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

The Anthropocene as a Geological Time Unit hardback or ebook

Other recommended books mentioned in this review:

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“The Deep: The Hidden Wonders of Our Oceans and How We Can Protect Them“, written by Alex Rogers, published by Wildfire in April 2019 (hardback, 366 pages)

I find the deep ocean one of the most fascinating ecosystems on our planet. Perhaps it is the final-frontier aspect, as so much of it remains unexplored (Rogers gives some mind-boggling statistics), or maybe it is the otherworldliness of its inhabitants, but I cannot get enough of reading more about it. Rogers’s fascination started at an early age, encouraged by summer holidays spent out on the ocean with his grandfather, an Irish fisherman. Although he recounts these formative experiences with great fondness, he also recognises the cruelty visited upon the unfortunate fish and lobsters that were caught.

A research career in marine biology followed and Rogers relates with great enthusiasm some of the highlights in marine science that he has lived through. Hydrothermal vents had only just been discovered in 1977 (see also The Ecology of Deep-Sea Hydrothermal Vents), and he participated in expeditions that first explored these deep-sea hot springs in the unruly waters of the Southern Ocean using remotely operated underwater vehicles. There was the ten-year Census of Marine Life (see also Discoveries of the Census of Marine Life: Making Ocean Life Count). And, of course, technological developments allowed both manned and unmanned submersibles to venture deeper, capture better footage, and even carefully return samples to the surface (see also Discovering the Deep: A Photographic Atlas of the Seafloor and Ocean Crust and In Oceans Deep: Courage, Innovation, and Adventure Beneath the Waves).

This is the wonder in this book.

The furry yeti crabs, the dream-like towers of black smokers hiding in the abyss, the millennia-old corals, the predators that are all mouth and stomach. And do not get me started on the fish (see also my review of Deep-Sea Fishes: Biology, Diversity, Ecology and Fisheries). Rogers’s eyewitness descriptions of the bizarre fauna are mesmerizing. The colour plate section is only all too small.

“The furry yeti crabs, the dream-like towers of black smokers […]The colour plate section is only all too small”

Here is another strong suit of The Deep: Rogers shows the relevance of seemingly obscure scientific research. The confirmation that the deep-water coral species Lophelia pertusa – so different from tropical species – builds reefs might seem like academic arcana to outsiders. But it was decisive in a UK court judgement to recognise the continental margin of the UK (and by extension that of the European exclusive economic zone) as habitat in need of protection from oil exploration and other activities under the European Habitats Directive.

Rogers is that rare breed of scientist who is not content losing himself in his research. He has advised conservation NGOs, provided testimony in court, and worked on projects for the UN to name but a few achievements. He cares intensely and his fighting spirit shines through in his writing.

This is the horror in this book.

See, one of the biggest problems with the open ocean is its remoteness and its lawlessness (see also my review of The Outlaw Ocean: Crime and Survival in the Last Untamed Frontier). Large parts of the oceans fall outside national jurisdictions and are effectively a marine wild west. Rogers effortlessly switches between the wonders of the denizens of the deep that we are only just beginning to discover, and the horrors of their destruction before we have even had the chance to properly take stock of what is out there.

“[…] the denizens of the deep [are destroyed] before we have even had the chance to properly take stock of what is out there “

The Deep is bang up-to-date on this front. There is the familiar spectre of overfishing: the rise of the industrial fishing complex, the harmful government subsidies, the collapse of fish populations, the destructive practice of trawling, the infuriating wastefulness of by-catches and simply catching more than the market can handle (see my reviews of All the Boats on the Ocean: How Government Subsidies Led to Global Overfishing, Daniel Pauly’s Vanishing Fish: Shifting Baselines and the Future of Global Fisheries, and The Curious Life of Krill: A Conservation Story from the Bottom of the World, and references therein). But Rogers is equally at ease explaining the details behind ocean acidification, eutrophication with concomitant episodes of oxygen depletion and algal blooms (a topic I am intimately familiar with from my own studies), changing ocean temperatures and coral bleaching, and palaeoclimatological evidence of past changes (see also my review of The Oceans: A Deep History).

And then there is pollution. So much pollution. Untreated wastewater and sewage, discarded and lost fishing gear, oceanic garbage patches and microplastics (see Microplastic Pollutants and Microplastic Contamination in Aquatic Environments: An Emerging Matter of Environmental Urgency), persistent chemicals that accumulate in the food chain. Even something as topical as the chemical oxybenzone in sunscreen, recently banned in Hawai’i, is mentioned. And Rogers is warily eyeing up the imminent threat of deep-sea mining, as the world continues to hunger for rare earth elements (see also The Elements of Power, and the double-act Deep-Sea Mining: Resource Potential, Technical and Environmental Considerations and Environmental Issues of Deep-Sea Mining: Impacts, Consequences and Policy Perspectives).

“[…] Rogers is warily eyeing up the imminent threat of deep-sea mining, as the world continues to hunger for rare earth elements”

Amidst this onslaught, Rogers continues to fight and eschews cynicism (though his success in court surprised even him). As opposed to terrestrial ecosystems, few marine species have yet gone extinct and fish populations can rebound if given the chance (see my review of Ocean Recovery: A Sustainable Future for Global Fisheries?). He convincingly shows that marine protected areas are a vital tool to offer fauna and flora a safe haven (see e.g. Marine Protected Areas: A Multidisciplinary Approach and Marine Conservation), and joins E.O. Wilson in his call to set aside large tracts of the planet (see Half-Earth: Our Planet’s Fight for Life).

The Deep is an absorbing and passionately written book that successfully combines an eyewitness account of the biological bounty of the deep sea with first-hand reporting on the threats, the conservation initiatives, the (failure of) policies and treaties, the fierce industry lobbying, and the political shenanigans. The Deep is aimed at a general audience and Rogers has decided to leave out literature references, footnotes, and an index. But those omissions are a small price to pay. At a time when we need as many people as possible to take notice, and when a documentary such as Blue Planet II can shake a nation out of its stupor on plastic pollution, good storytelling is a necessary and promising approach.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

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“Origins: How The Earth Made Us“, written by Lewis Dartnell, published in Europe by The Bodley Head (a Vintage imprint) in January 2019 (hardback, 346 pages)

Dartnell takes as his starting point the evolution of Homo sapiens in East Africa. He subscribes to Maslin’s ideas for where and when we evolved, outlined in The Cradle of Humanity: How the Changing Landscape of Africa Made Us So Smart. The gist of his argument was that it was a combination of plate tectonics and climate. The geography of the African rift valley and pulses of climate variability interrupting longer periods of stability led to regional lakes rapidly appearing and disappearing. This unstable environment favoured adaptability and intelligence. Dartnell similarly gives a revealing geological explanation reaching back 55 million years for how the most recent ice age came about and how it has impacted human dispersal around the world.

Now, it is easy to accuse a popular science book like this of glossing over subtleties for the sake of a good story. I therefore appreciated that Dartnell clearly signposts there are frequent disagreements on the details of the story of human evolution, and that not all evidence points in the same direction: his narrative represents the consensus view. He is nuanced enough to point out what that may seem rapid and purposeful – humanity’s global migration starting 60,000 years ago – was, in fact, a matter of trial and error. I liked his suggestion that there may have been earlier attempts at migrating out of Africa, or developing agricultural civilizations, that simply fizzled out before taking off. Similarly, when he brings up the effects of the Toba eruption on early humans (see my review of When Humans Nearly Vanished: The Catastrophic Explosion of the Toba Volcano), he immediately flags this up as controversial. All this gave me a good feeling about the balance Dartnell is trying to strike between presenting a captivating narrative while sticking to the facts and how best to interpret them.

“there may have been earlier attempts at migrating out of Africa, or developing agricultural civilizations, that simply fizzled out before taking off.”

From this point forward, the remainder of the book deals with the last 10,000 years of human civilization, making excursions into deep time explanations where needed. For readers of Diamond’s Guns, Germs and Steel: A Short History of Everybody for the Last 13,000 Years this is perhaps more familiar territory as he discusses the rise of agriculture (see also my review of Against the Grain: A Deep History of the Earliest States for some nuanced counterpoints to the standard narrative) and livestock husbandry. Here he reaches back into deep time to explain why Eurasia ended up with so many more domesticable species compared to the Americas, and why the orientation of the continents made the spread of agriculture easy in Eurasia (which is oriented East-West), but hard in the Americas (which is oriented North-South).

With agriculture came trade and Dartnell chronicles the establishment of the first maritime and overland trade routes, leaning heavily on overview works such as The Sea and Civilization: A Maritime History of the World and The Silk Roads: A New History of the World. His interest is in how these were shaped by the geography of the seas (the shape of coastlines, the existence of naval bottlenecks) and the land (the ruggedness of the terrain, microclimates). And he explores how our subsequent maritime Age of Exploration, when Western nations started colonising countries around the globe, depended on, and was shaped by, the planetary patterns of ocean and air currents, in turn shaped by where plate tectonics has parked the continents currently.

In the same vein, he spends two chapters exploring the deep origin of the materials we use to build and construct with (whether architecture or objects and tools), how they are formed, how they have ended up distributed over the world the way they have, and how that has played into the fortunes of civilizations and nations. He talks of rocks and metals and does an excellent job explaining our current dependence on rare earth elements and platinum group metals.

“90% of the coal we have used since the Industrial Revolution was formed during the Carboniferous […] if that had not happened, would the Industrial Revolution have taken off?”

He is concerned about our continued appetite for these resources. His arguments got me thinking, and I wonder whether we might be reaching a hard limit. When our increasingly advanced machinery and electronics depend on almost all the elements in the periodic table, where do you go from there? These materials are – if not always rare – hard to obtain, and there are often no suitable replacements. When you depend on finite resources like that, and things like renewable energy technology and computers cannot function without, can we continue to science and engineer our way out of our problems? I get the feeling this is rarely thought or talked about when considering the future. Similarly, he convinces that transitions throughout our history have acted as a ratchet, allowing us to expand and increase our population to a point where there is no turning back (or at least not without drastically decreasing the size of our global population) – we would not be able to feed, clothe, and shelter this number of people anymore with yesterday’s technologies.

Finally, he gives a quick tour of energy (see also Energy and Civilization: A History) and how we transitioned from muscle power to wind and water power and then fossil fuels, taking the reader through the age of coal, the steam engine and then oil. Here, too, he is specifically interested in how these resources were formed and why they are found where they are found. From reviewing Energy: A Human History and Carboniferous Giants and Mass Extinction: The Late Paleozoic Ice Age World I was already familiar with the fact that 90% of the coal we have used since the Industrial Revolution was formed during the Carboniferous, some 360-300 million years ago (leading Dartnell to ask the same question as Rhodes in the former book: what if that had not happened, would the Industrial Revolution still have taken off?) But Dartnell provides a lucid geological explanation to the question why so much coal was formed then. And it turns out there was a similar period in which the vast majority of the world’s oil reserves were formed, again for a good geological reason.

In his book The Equations of Life: The Hidden Rules Shaping Evolution, Charles Cockell wrote that physics is life’s silent commander, setting hard limits on what evolution can and cannot do. I would argue that Dartnell here similarly convinces that geology is history’s silent commander. Very accessible and full of interesting ideas, Origins is a worthy contender in the saturated market of big history and environmental history books. Depending on how much you have read on this topic, not everything here will be novel, but I do think that with its deep time and geology perspectives, Dartnell goes a few steps beyond most books.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Origins paperback, hardback, ebook or audiobook

Other recommended books mentioned in this review:

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“Climate Change and the Health of Nations: Famines, Fevers, and the Fate of Populations“, written by Anthony J. McMichael and edited by Alistair Woodward and Cameron Muir, published by Oxford University Press in February 2017 (hardback, 370 pages)

Anthony J. McMichael was an epidemiologist associated with various renowned academic institutes during his life and advised the Intergovernmental Panel on Climate Change (IPCC) on the link between climate change and health (see this obituary for a fuller description of his many achievements and contributions). With the manuscript for this book accepted for publication, he suddenly passed away in September 2014. Alistair Woodward and Cameron Muir took up the torch and saw the book through to publication.

There is obviously increasing concern what future climate change will have in store for humanity and the planet at large. And there is no shortage of dire predictions of more frequent extreme weather events, sea level rise, impact on agriculture, and the risk of disrupted food production accompanied by conflict and unrest. This is not mere idle speculation or hypothetical model forecasting, says McMichael. Our past is littered with episodes where natural climatic changes caused all sorts of misery. The key to understanding what might come next lies in an understanding of our past.

“Our past is littered with episodes where natural climatic changes caused crop failures, famines, warfare and the demise of civilizations.”

The first few chapters give the reader all the relevant background knowledge needed. McMichael introduces the various mechanisms that cause longer and shorter-term climate fluctuations, from Milankovitch cycles to decadal oscillations such as El Niño. The result, as I mentioned in my review of The Oceans: A Deep History, is a fiendishly complex system of feedback loops. He gives an overview of the various direct and indirect health impacts that climate change can have, and provides a short history of the rise of humans and the beginning of agriculture (see also my review of Against the Grain: A Deep History of the Earliest States). McMichael speaks of the Faustian bargain we unwittingly made by transitioning from nomadism to farming. Palaeopathology has documented how our health suffered due to our change in diet (see Built on Bones: 15,000 Years of Urban Life and Death, or my review of Evolution’s Bite: A Story of Teeth, Diet, and Human Origins), but this new sedentary lifestyle also made us more vulnerable to climatic changes.

The centrepiece of the book is his synthesis of some 11,000 years of environmental history. Starting with early civilizations in or near the Nile Valley, he walks us through the civilizations of the Sumerians, Akkadians, Babylonians, Egyptians, Hittites, and, in the Indus Valley, the Harappans. For most of these, the lack of written records means that we have pieced together their history from archaeological and palaeoclimatological data. We have a far more detailed picture of the rise and fall of Roman, Mayan, and Anasazi civilizations, and, later, of the Little Ice Age (ca. 1300-1850), the eruption of Mount Tambora, and the Irish potato blight. Throughout, McMichael summarises how droughts, floods, or changing temperatures are linked to famines, the spread of diseases, warfare, mass migrations (whether as climate refugees or as groups hell-bent on conquest), and, ultimately, the fate of empires.

“McMichael speaks of the Faustian bargain we unwittingly made by transitioning from nomadism to farming.”

Now, there is a vast literature on the link between climate and human history, so this book necessarily takes a bird’s eye view. Next to the academic literature, you could build a small library with more popular books from the likes of Jared Diamond (see Collapse: How Societies Choose to Fail or Survive) and especially Brian Fagan (see The Long Summer: How Climate Changed Civilization, The Great Warming: Climate Change and the Rise and Fall of Civilizations, and Floods, Famines, and Emperors: El Niño and the Fate of Civilizations). Early eras are covered in, for example, Climate Change in Prehistory: The End of the Reign of Chaos, but there are also excellent books on Roman civilization (see my review of The Fate of Rome: Climate, Disease, & the End of an Empire), the Little Ice Age (see The Little Ice Age and my review of Nature’s Mutiny: How the Little Ice Age Transformed the West and Shaped the Present), and the impact of the Tambora eruption (see Tambora: The Eruption That Changed the World and Tambora and the Year without a Summer: How a Volcano Plunged the World into Crisis).

What sets this book apart is the synthesis of this vast and fascinating topic, making it a good starting point, and its explicit link to health and disease. Off the top of my head, the only other book that does something similar is Climate Change and the Course of Global History: A Rough Journey, but McMichael’s background as an epidemiologist and his work for the IPCC position him very well to tell this story.

One of the things I liked was the author’s caution throughout the book. So, when he mentions the possible impact on our very early history of the Toba eruption (see my review of When Humans Nearly Vanished: The Catastrophic Explosion of the Toba Volcano) or the question whether the Black Death in 16th-Century Europe was actually caused by bubonic plague (see for example Return of the Black Death: The World’s Greatest Serial Killer or Biology of Plagues: Evidence from Historical Populations), he gives a brief overview of why these ideas are considered controversial. When, in the final chapters, it comes to forecasts and lessons for the future, he is similarly moderate. Never before has our population reached such large numbers, and to see comparable levels of atmospheric carbon dioxide we have to go back tens of millions of years in palaeoclimatological records. So, without downplaying the important lessons that history holds for the future, in some ways the future is not like the past.

“even though I am familiar with [this topic], the way it is brought together and puts time into perspective still gave me near-vertigo.”

The dumb thing is, even though I am familiar with all the individual pieces McMichael lays out here, the way it is brought together and puts time into perspective still gave me near-vertigo. Clearly, no empire ever looked much ahead or entertained the idea of their demise until it was almost upon them. McMichael highlights how evolution, always aiming to help organisms survive the now, has left us poorly equipped to plan for the longer-term. While the full story of most civilizations has spun itself out over many centuries, our “Great Acceleration” and the growth of the world’s population from 1.5 to 7+ billion people took just decades (see my review of The Great Acceleration: An Environmental History of the Anthropocene Since 1945).

Even if, for the sake of argument, human-induced climate change was not on the menu, have we, through our technological advances, created a robust society able to weather climate fluctuations far into the future? Or have we mindlessly expanded to the maximum carrying capacity allowed by our environment? I think we all know the answer to that (see also my review of Never Out of Season: How Having the Food We Want When We Want it Threatens Our Food Supply and Our Future). It is a tall order to look at the totality of the picture revealed here and remain as optimistic as the author – though his mindset does not take away from the urgency of his message.

The only minor quibble I have with this book is that some of the sourced illustrations were designed with colour in mind and have here been reproduced in greyscale, limiting their usefulness. That notwithstanding, Climate Change and the Health of Nations is a fascinating and thorough synthesis that shows how history holds many valuable lessons for those willing to listen. The book is also a fitting testament to McMichael’s long career, and Woodward and Muir, as well as the publisher, are to be commended for making sure this book saw the light of day.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Climate Change and the Health of Nations paperback, hardback or ebook

Other recommended books mentioned in this review:

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“Like inexperienced but overconfident drivers, we accelerate into landscapes and ecosystems with no sense of their long-established traffic patterns, and then react with surprise and indignation when we face the penalties for ignoring natural laws”.

And with that, she had me hooked.

“Timefulness: How Thinking Like a Geologist Can Help Save the World“, written by Marcia Bjornerud, published by Princeton University Press in September 2018 (hardback, 208 pages)

Bjornerud assumes little geological background knowledge on behalf of her readers and uses the first two-thirds of the book to give a canned history of relevant discoveries, including: past estimates of Earth’s age and the conceptualisation of deep time (cf. Four Revolutions in the Earth Sciences: From Heresy to Truth), the use of isotopes to date rocks (cf. Nature’s Clocks: How Scientists Measure the Age of Almost Everything), past climates as reconstructed from ice cores (cf. The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change and Our Future), the basics of geomagnetic reversals, spreading mid-ocean ridges, and plate tectonics (cf. The Spinning Magnet: The Force That Created the Modern World – and Could Destroy It and The Tectonic Plates are Moving!), the deep history of earth’s atmosphere and the increase in oxygen (cf. Oxygen: A Four Billion Year History and Oxygen: The Molecule that Made the World), and a short section on mass extinctions (cf. The Ends of the World: Volcanic Apocalypses, Lethal Oceans and Our Quest to Understand Earth’s Past Mass Extinctions). From the above, you can see that many of these topics have been discussed at length in other books, quite a few of which I have reviewed recently on this blog.

The last two chapters are where Bjornerud tries to tie this all together. She introduces the concept of the Anthropocene, and how geologists define this by pointing out that humans are now a geologic force unto themselves. Processes like erosion and sedimentation, sea-level rise, and extinction are happening – and ocean acidity and atmospheric carbon dioxide are changing – at rates many times the background rates of recent millennia (see my review of The Anthropocene as a Geological Time Unit).

“the immensity of deep time: all of our recorded history has occurred in a single climatically relatively stable interglacial period”

If there is one observation that never fails to impress upon me the immensity of deep time, it is the following: ice core studies have revealed how all of our recorded history, all roughly ten-thousand years of it, has occurred in a climatically relatively stable interglacial period (a period between ice ages). These same studies have also shown that during the last 2.6 million years, known as the Pleistocene, there have been 30 (!) such changes between ice ages and interglacial periods.

To see a world where carbon dioxide levels are comparable to what is expected in the near future if emissions are not curbed, we have to go back 55 million years, to the Paleocene-Eocene Thermal Maximum (or PETM for short). This section allows Bjornerud to introduce positive feedback loops and the lurking danger of methane currently frozen in permafrost and underwater deposits known as clathrates (cf. The Oceans: A Deep History and Brave New Arctic: The Untold Story of the Melting North). She also shortly dwells on technological solutions such as carbon capture and storage (CCS for short) and geo-engineering (cf. The Planet Remade: How Geoengineering Could Change the World), finding fault with both.

The final chapter is where she tries to convince the reader that thinking like a geologist can save the world. I admit that I came away with mixed feelings. Some of her suggestions border on the spiritual – a brief excursion into how e.g. Buddhism or Norse mythology treat the concept of time and connect to it. Some seem gimmicky – conceptual art that plays with time such as Daniel Hillis’s 10,000 year clock or the ongoing 639-year performance of a John Cage composition. Others are great – pointing out the short-sightedness ingrained in democratic election cycles and the need for long-view leadership. Examples of the last are the native American idea of basing decision making on its likely effects on unborn generations (the Seventh Generation principle) or Kurt Vonnegut’s call for a governmental Department of the Future that represents future generations. Bjornerud envisions geology becoming a far more important part of school curricula, instilling a better conception of deep time in pupils.

“[…] humans are now a geologic force unto themselves.”

To my surprise, I finished this book feeling ever so mildly unsatisfied. I do not think this book deserves a negative judgement though, so let me try and be more specific. First, I am probably not the prime target audience for it – given the canned history she provides, my impression is that Bjornerud is aiming at an audience with little to no knowledge of geology. I have been reading up on many of these topics lately, so a lot of it was not new to me. Second, based on the announcements, I had perhaps unreasonably high expectations, and I felt she could have made more of some of the material on mixing times, rates of Earth phenomena, and length of certain geological cycles that she now relegates to an appendix. Third and final, what about overpopulation? (cf. Should We Control World Population? – sorry if I sound like a stuck record). If you point out the incredible acceleration in increasing carbon dioxide levels in recent decades, why not ask why this happened? (My answer: a burgeoning population that is increasingly affluent. I am sure we could all have our cake and eat it if there were not so many diners). Although unregulated population expansion is also a form of short-sightedness, this has little to do with geology. So, although I like to think Bjornerud has thought about overpopulation, leaving it out of this book is perfectly understandable.

I would urge potential readers not to let above personal considerations discourage too much. The take-home message is that Bjornerud writes extremely well and I found the book a thoroughly captivating and enjoyable read. If you lack geologic background knowledge, many of the concepts presented here will no doubt astound you and help you conceptualise deep time better. I admit that even I picked up new bits of information. The book also has some very handsome, hand-drawn illustrations by Haley Hagerman that help out. Bjornerud is on form when she castigates humanity for its short-sightedness, and her plea for a more time-literate society is convincing. Many geologic biographies of our planet have been written, but Bjornerud here presents a unique take on this genre.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Timefulness paperback, hardback, ebook, audiobook or audio CD

Other recommended books mentioned in this review:

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“Land Bridges: Ancient Environments, Plant Migrations, and New World Connections“, written by Alan Graham, published by The University of Chicago Press in March 2018 (paperback, 310 pages)

Graham has spent decades researching the vegetation history of North and Latin America. Next to numerous papers, he has written three books on the topic (Late Cretaceous and Cenozoic History of North American Vegetation: North of Mexico, and more recently Late Cretaceous and Cenozoic History of North American Vegetation: North of Mexico and A Natural History of the New World: The Ecology and Evolution of Plants in the Americas). The expert will want to have these at hand as background to this book, though the general reader can take them as a given.

Given this research focus, Graham here discusses five New World land bridges that formed or disappeared over the last 100 million years. For each of these, he summarises the current climate, vegetation, and geographic setting, followed by their geologic history and their utilization by organisms, as revealed by (foremost) plant fossils. Where applicable, the role of these land bridges in human prehistory is also discussed. I also kept the recently reviewed Earth History and Palaeogeography at hand as a reference work. Although Graham provides a few maps and links to a useful interactive tool called EarthViewer over at BioInteractive, I find this book very useful for the current big picture on where all the continents were over time.

“The Bering Land Bridge […] plays an outsized role in our collective imagination as the likely route by which human beings peopled the Americas”

Out of the land bridges discussed, three are the archetypal “strips of land between continents”: the currently existing Central American Land Bridge, the recently defunct Bering Land Bridge between Siberia and Alaska, and the long-gone Magellan Land Bridge between southern South America and Antarctica.

The first of these likely formed some 3 million years ago, as evidenced by the so-called Great American Biotic Interchange where flora and fauna started showing up on the other side of the bridge in the fossil record. Similarly, changes in the marine fauna, which became separated in what were now the Atlantic and Pacific oceans, also support this date. Some scientists want to push it back to 10-15 million years ago, but Graham thinks the weight of the evidence is not on their side so far. The Bering Land Bridge has been in place since roughly the Paleogene, some 65 million years ago, but has been submerged on and off as sea levels rose and dropped in tandem with climatic changes. It plays an outsized role in our collective imagination as the likely route by which human beings peopled the Americas (I first mentioned it here in my review of Fagan’s Fishing: How the Sea Fed Civilization but see also First Peoples in a New World: Colonizing Ice Age America). On the other side of the planet, the Magellan Land Bridge connected South America and Antarctica until the Drake Passage opened up some 34-29 million years ago.

The other two bridges are less archetypal. The Antillean Land Bridge was never a bridge proper. Although some scientists favour this idea, and some of the Caribbean islands were connected in the past, Graham supports the idea of a “stepping stone” bridge. Most islands are close enough that animals and plants can relatively easily hop, float, or blow across. The last land bridge here considered feels a bit like a stretch (pardon the pun). The North Atlantic Land Bridge is the huge swathe of land that connected Europe with Greenland and Canada before they got interrupted by the formation of the North Atlantic.

This book provides a far more detailed picture of the geological details of these specific areas than Torsvik and Cocks could logically fit into Earth History and Palaeogeography, and I found the details surrounding the various lines of evidence as to when these bridges existed or disappeared really quite interesting. Graham further livens up selected chapters with episodes from history, regaling the reader with tales of explorers such as Vitus Jonassen Bering or Ernest Shackleton.

“This is juxtaposed with the hardcore data on palaeobotany that I found less riveting (sorry botany, you were never my greatest love), but for the specialist, this will be exceedingly useful”

This is juxtaposed with the hardcore data on palaeobotany. What Graham makes very clear is that the fragmentary fossil record, and the many misidentified species in museum collections and herbaria greatly hamper interpretations. Even so, land bridges emerge as one of several routes by which plants have spread in the past, with dispersal by wind, water, and animals such as birds being important additional possibilities. Next to frequent references to his previous three books, a lot of the data is tucked away in an online supplement where Graham lists over 200 pages of additional tables in 25 PDF files. I admit that for a general reader such as myself these sections were less riveting (sorry botany, you were never my greatest love), but for the specialist, this collation of data and literature references will be exceedingly useful.

One thing that hampers this book slightly is the reproduction quality of the images. The paperback copy that I reviewed is printed by Lightning Source in the UK, which means it is digitally rather than offset printed if I’m not mistaken. For the black-and-white photos, this results in a grainy though acceptable reproduction, but the custom-made maps have a fair bit of writing on them. They have here been reproduced in greyscale rather than colour and are quite small which makes it hard to read all the details. The reproduction of maps and illustrations from other publications varies, depending on the quality of the source files, and, with a few exceptions, is decent to good.

Overall then, this book will be of interest to a select audience. Its primary value will be as a reference work for palaeobotanists and (palaeo)biogeographers but it is also attractive to lay readers such as myself who have a strong interest in geology and palaeontology. Graham has done a remarkable job carefully enriching the book with many interesting geological, archaeological and historical details, providing a broader picture of the role of land bridges.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Land Bridges paperback, hardback or ebook

Other recommended books mentioned in this review:

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“The Oceans: A Deep History“, written by Eelco J. Rohling, published by Princeton University Press in January 2018 (hardback, 262 pages)

I will come right out and say that I found this book a challenging read. Partly this is because my background is not in geochemistry, and there is quite a bit of that here, partly this is because, whether you like it or not, the Earth system is complex. Fiendishly complex. Trying to put into words the many interlocking feedback mechanisms playing out on different timescales will, therefore, make for dense reading in places.

The Oceans starts off with three introductory chapters that are quite technical, featuring a lot of oceanographic, geochemical, and atmospheric chemistry details necessary to understand the rest of the book. There are a number of helpful illustrations in this section that the reader will be referred to time and again. It is not until page 83 that Rohling starts his journey through the deep history of our oceans. To structure the book, he has chosen three key topics important to our understanding of past and current climate fluctuations.

“[…] the Earth system is complex. Fiendishly complex.”

The first thing most people will think of when you mention climate change is temperature, and Rohling walks the reader through reconstructions of Earth’s thermal record. There were times where our planet was frozen solid (periods appropriately known as Snowball Earth), such as the Huronian glaciation between 2.4 and 2.1 billion years ago, and more “recently” in the Neoproterozoic Era between 750 and 580 million years ago. The latter was followed shortly by the famous Cambrian explosion, an episode in Earth’s history where life flourished. During the reign of the dinosaurs, the world has been much hotter, with average temperatures some to 10°C to 15°C higher than they are today. This chapter is a good example of the challenge of putting into words the complex interplay between the organic and inorganic carbon cycles, as fluctuations in atmospheric carbon levels are responsible for these long-term temperature swings.

The second topic, of much relevance today as well, is ocean acidification. As Rohling explains throughout the book, the oceans are an enormous buffer for carbon. But just as the oceans aren’t a featureless bathtub (see the introduction to Deep-Sea Fishes: Biology, Diversity, Ecology and Fisheries for a good overview of ocean topography), they are also not a chemically inert bathtub. Levels of dissolved carbon dioxide change the acidity of water, which affects shell-bearing organisms large and small. One episode where strong ocean acidification is implied is the end-Permian mass extinction some 252 million years ago, which was so vividly described in Brannen’s book The Ends of The World: Volcanic Apocalypses, Lethal Oceans and Our Quest to Understand Earth’s Past Mass Extinctions, and is the subject of Benton’s When Life Nearly Died: The Greatest Mass Extinction of All Time. A more recent, and therefore better documented, episode was the Paleocene-Eocene Thermal Maximum some 56 million years ago. During both these events, large amounts of carbon dioxide were released relatively quickly (several tens to hundreds of thousands of years is quick geologically speaking), leading to drops in oceanic acidity. The Ammonoids, the now-extinct group of cephalopods that we met in Staaf’s Monarchs of the Sea, was one group that was heavily hit during the end-Permian extinction episode.

The final topic that is hugely influential for life is water’s oxygen content. Lack of oxygen in water is also known as anoxia. Ocean Anoxic Events are periods of prolonged (hundreds of thousands of years) and widespread (possibly global) lack of oxygen. This, too, has relevance today as water pollution is once again leading to persistent “dead zones“; regions of the deep sea that remain devoid of oxygen for months or years at a time, choking most life forms to death. Ironically, the layers of putrefying organic material that build up during these historic Ocean Anoxic Events were slowly transformed into black shales, of much interest to the fossil fuel industry today.

“Our inability to conceptualise deep time is a huge problem […]”

Throughout the book, Rohling in passing mentions the important messages deep history has for our current times, but a book like this of course has to have a chapter explicitly dealing with current climate change. Looking at deep history, what makes the last 200 years different is not necessarily the amount of carbon we have so far released through the burning of fossil fuels, it is the speed. Conditions on our planet are changing faster than any time before, based on our reconstructions from Earth’s deep history, with the rate of change rivalling or exceeding even that seen during the end-Permian mass extinction. The two hundred years since the Industrial Revolution may seem like ages to humans, but they are a blip in deep history. Our inability to conceptualise deep time is a huge problem, something that is discussed in-depth in Bjornerud’s book Timefulness: How Thinking Like a Geologist Can Help Save the World.

And that is where this book shines. By surveying what the palaeoclimatological record reveals, by describing all the feedback mechanisms we have uncovered, it becomes abundantly clear that denying that current climate change is happening is absurd. Denialists both love to argue the quantitative details and grossly simplify them. Why can we not predict how much sea levels will rise exactly? Why is it not getting hotter everywhere? And yes, the finer details and timing of what awaits us are subject to a certain amount of uncertainty and are based on forecasts and modelling studies, subject to revision (guys, for f**** sake, this is how science works). But by attacking the quantitative details they are missing the bigger picture. Qualitatively speaking none of the changes that are forecasted are based on conjecture: Earth’s deep history, as explained here so in-depth, tells us what happens when our atmosphere and oceans change. People want to shrug this off and say “but the planet recovered, right? We are here today!” But this again painfully highlights our inability to conceptualise deep time. The natural geochemical processes that can undo rising temperatures or increased ocean acidity play out over hundreds of thousands of years. So, yes, the planet will recover from us, but we will not like the ride there.

The Oceans, then, is a book with many relevant lessons to understanding climate change today. Whether the dense material will reach the people who need to see it most is something I am doubtful of. But if you want to understand how our oceans work, and how they have influenced life as we know it, this book is mandatory reading that thoroughly covers the subject. Be prepared to engage your brain while reading it though.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however. You can support this blog using below affiliate links, as an Amazon Associate I earn from qualifying purchases:

Rohling’s The Oceans paperback, hardback or ebook

Other recommended books mentioned in this review:

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