What a killer title. Rarely have I seen three snappy words so effectively capture the essence of a concept in biology. What concept is that? Zoogeochemistry. Many scientists have convincingly made the case that it is the small things that run the world. Though it is undeniably true that e.g. microbes and insects have shaped our planet, and continue to do so, it would be a mistake to think that larger animals are just along for the ride. I was stoked the moment the announcement for this book dropped and conservation biologist and marine ecologist Joe Roman did not disappoint. Eat, Poop, Die is fun and fascinating, while always keeping one eye firmly on the facts and complexities of ecology. Is it too soon to start earmarking titles for this year’s top 5? I think not.

Eat, Poop, Die: How Animals Make Our World, written by Joe Roman, published in Europe by Profile Books in April 2024 (hardback, 277 pages)

Given that this concept “is the beating heart of this book” (p. 214), what is zoogeochemistry? Physical forces shape the living world and living forces can shape the physical world right back—you may well have heard of biogeochemistry. Traditionally, research has focused on bottom-up interactions, revealing how e.g. microbes influence the climate and fungi and invertebrates help form soils. The phrase “ecosystem services” is often bandied about in this context, referring to how organisms keep our planet liveable by fertilizing soils, filtering water, or absorbing carbon dioxide from the atmosphere. Increasingly, however, it is becoming clear that larger animals similarly have the power to shape ecosystems, influencing the flow of chemical elements at large scales. Hence zoogeochemistry. How do animals do this? The title of the book says it all: rotting carcasses, deposited faeces, “and other unglamorous forces” (p. 52) can collectively move nutrients around ecosystems and influence the climate.

By visiting and interviewing fellow ecologists, and mixing in some of his own research, Roman introduces you to a variety of very interesting studies that are now uncovering these processes. He starts simply enough with the volcanic island Surtsey which appeared above the waves off the coast of Iceland in 1963. It has offered a unique opportunity for ecologists to study how a newly formed island gets colonized by plants and animals, with birds and seals enriching the initially scrappy plant communities through faeces, urine, carcasses, and eggshells. In the oceans, zooplankton move carbon and other elements from the surface to the deep , forming one component of the so-called biological pump. But whales, because of their sheer size, have the potential to counteract this. By bringing nutrients back from the deep, where they feed, to the surface, where they release nutrient-rich faecal plumes, they form what Roman calls a whale pump. (This happens to be his speciality, so expect a fair bit of lyrical waxing about whale poop.) In the Maasai Mara, wildebeest that die in river crossings provide an annual nutrient pulse, on top of the steady and intense input of hippos pooping in their pools. Coral-crunching parrotfish poop out the sand that covers the beaches of many tropical holiday destinations, and when periodical cicadas die in their trillions, they provide enormous but irregular nutrient pulses that have barely been studied. Roman appropriately concludes the book with James Estes’s work on sea otters in Alaska that has become the poster child for the concept of trophic cascades. In the process, he provides the interesting backstory of how the United States Atomic Energy Commission left a legacy of both atomic test sites and translocated otters that would repopulate the Pacific coast of the USA, a backstory Estes did not really detail in Serendipity. These and other examples form a delectable list of study systems, each more interesting and unbelievable than the last. No wonder Roman is often asked: “How did we overlook this for so long?”

“rotting carcasses, deposited faeces, “and other unglamorous forces” (p. 52) can collectively move nutrients around ecosystems and influence the climate.”

What I particularly appreciated is that for some of the better-studied systems, Roman gets the nuances right. The story of wolf reintroduction in Yellowstone National Park suppressing elk overgrazing and leading to a restored ecosystem has almost become a meme in ecology. The details, however, are a bit more complicated than the idea that you can just sprinkle wolves over a broken ecosystem like some sort of magical fairy dust. Similarly, the notion that bears indirectly fertilize trees by littering the forest with salmon carcasses, which Suzanne Simard approvingly mentioned in Finding the Mother Tree, has a few detractors. Roman spends time in the field with Daniel Schindler who thinks that poorly executed science and overinterpreted stable-isotope data have created a good story. One of his students adds that, though the cycling of nutrients between different animals in this system is not in question, the idea that it also fertilizes trees with nitrogen is considered more shaky by some. When it comes to the Pleistocene extinction of megafauna, Roman again hits the nail on the head by acknowledging the debate about the relative contributions of human hunting and a changing climate.

Eat, Poop, Die avoids becoming an endless showcase of stories about animals moving nutrients around ecosystems in said fashion. Chapter 5 (Chicken Planet) could have easily concluded the book but instead sits smack in the middle, punctuating the flow nicely. These sombre crescendos partially answer Roman’s earlier question of why we have overlooked the role of large animals for so long: because many have been driven to near-extinction by humans. The consequences of this have been studied in quite some detail for whaling, which resulted in impoverished marine ecosystems. But similar landscape changes resulted from the North American fur trade that saw the slaughter of bison, beavers, and otters. Humans have since become the prime mover of nutrients, with the mining of guano islands one sordid chapter in that history. The Haber–Bosch process might nowadays provide plentiful nitrogen (at a large environmental cost), but phosphorus still has to be mined. Future shortage is one of those creeping problems that is often overlooked in environmental discourse.

“[The book presents] a delectable list of study systems, each more interesting and unbelievable than the last. […] I particularly appreciated that for some of the better-studied systems, Roman gets the nuances right.”

Twice, Roman ruminates on whether rewilding our planet could help restore the nutrient flows that we have disrupted. It certainly has a better track record than geoengineering proposals. He is honest enough to highlight the downsides of large animals again roaming the land (from beavers flooding properties to otters hunting large clams that are commercially fished) and acknowledges that certain scenes from the past would cause social upheaval today. Achieving E.O. Wilson’s vision of setting aside half the planet for nature is “a long shot, especially if people are still eating meat on the bone and the population is increasing from eight billion to nine billion or ten” (p. 236). The most outspoken he gets is when he concludes: “Look, there’s no way around it. […] we’re going to have to consume less, consume better, if we’re going to rewild the world. A managed retreat is the only reasonable approach” (p. 238). I agree, and I cannot but marvel at how he is quietly radical here, almost sneaking in under the radar the three proverbial f-bombs (“veganism”, “degrowth”, and “overpopulation”) that often spark heated discussions. Though I could slate Roman for not developing this much further, I recognize that these are complex topics that could easily fill several books, and it would take us too far away from the main theme of this book.

Eat, Poop, Die is an absolute stonker that captivates from start to finish. The topic of zoogeochemistry is an incredibly fascinating development in ecological research and Roman recounts it here with flair.

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

Eat, Poop, Die

Other recommended books mentioned in this review:

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This is the second of a two-part dive into the story of oceans on Earth and elsewhere, following my review of Ocean Worlds. That book gave a deep history of how our oceans shaped Earth and life on it and briefly dipped its toes into the topic of oceans beyond Earth. Alien Oceans is the logical follow-up. How did we figure out that there are oceans elsewhere? And would such worlds be hospitable to life? Those are the two big questions at the heart of this book. If there is one person fit to answer them, it is Kevin Peter Hand, a scientist at NASA’s Jet Propulsion Laboratory and their deputy chief for solar system exploration.

Alien Oceans: The Search for Life in the Depths of Space, written by Kevin Peter Hand, published by Princeton University Press in March 2020 (hardback, 248 pages)

A major question in astrobiology is whether the evolution of life on Earth is a fluke, or whether life is bound to pop up wherever conditions are favourable. Hand very neatly frames this in the bigger history of science. Over the centuries, we figured out that the laws of physics, chemistry, and geology work beyond Earth. But “when it comes to biology, we have yet to make that leap. Does biology work beyond Earth?” (p. 15). What we have learned is that life as we know it needs water. And though there is no shortage of theories on the origins of life, oceans are very likely where it started, and thus a logical first place to start looking for answers.

If you have any interest in astrobiology, you will probably have heard of the concept of a habitable zone or Goldilocks zone where, based on the distance to a star, conditions for life are just right. Not so close as to be too hot, nor so far as to be too cold. Earth obviously falls in that zone. Next to many minor insights, Alien Oceans had three major eye-openers for me. This was the first one:

There are other Goldilocks zones.

Depending on the details of their orbit, moons can experience such strong tidal tugs from their parent planet that the constant squeezing and stretching of the rock creates enough heat through internal friction to sustain liquid water. The physics of water helps, as it has a seemingly mundane but rather unusual property. Ice floats. When water solidifies, its density decreases slightly. What this means for moons is that the liquid water exposed to the cold of deep space freezes and forms a protective icy shell. Most liquids do not have this useful property. When they freeze, they sink to the bottom exposing more liquid until all of it is frozen solid. To top it off, ice is also a good thermal insulator, helping such ocean worlds retain heat. Maybe I have been hiding under a rock, but this was revelatory for me. Suddenly, the amount of cosmic real estate suitable for life has increased quite dramatically. And we have some of it right here on our doorstep.

“Over the centuries, we figured out that the laws of physics, chemistry, and geology work beyond Earth. But “when it comes to biology, we have yet to make that leap. Does biology work beyond Earth?“”

The existence of oceans in our solar system and how we gathered the evidence is one of the two major threads running through this book. Hand examines this in detail for Jupiter’s moon Europa, which has been studied in the most detail. Three types of data are typically gathered: spectroscopic, gravimetric, and magnetometric. This is where Hand gets fairly technical, though, fortunately, he extensively uses comparisons with everyday concepts and technologies to help you understand the underlying (astro)physics. Without retreading his careful explanations, in Europa’s case, these different strands of data all converge on a moon with an icy shell and a substantial subsurface ocean some 80–170 km thick as the best explanation. Mixed in with this narrative are the details and many technical setbacks of the Galileo mission that are nail-bitingly tense in places.

Similar missions and measurements have been done for Saturn’s moons Enceladus and Titan, Jupiter’s moons Ganymede and Callisto, Neptune’s moon Triton, and Pluto. The evidence for oceans gathered so far gets less robust in this order, but there are some notable variations on the theme. Enceladus ejects spectacular plumes of water and carbon compounds that were photographed and sampled by the Cassini–Huygens mission. Ganymede, meanwhile, is so large that the bottom of its ocean might consist of an exotic form of dense ice, ice III, formed at very high pressures not seen on Earth, meaning its ocean is sandwiched between two layers of ice.

So you have found exo-oceans. Now what? Can we expect to find life here? That is the second major thread. Hand identifies five conditions for life to emerge: a solvent such as water, chemical building blocks, an energy source, catalytic surfaces, and time. Interestingly, there is a gap between two schools of thought. The top-down explanation deconstructs life backwards in time until we arrive at an RNA world, but how did that get started? The bottom-up explanation has shown that life’s basic building blocks such as amino acids exist in space, but how do we go from there to larger functional molecules?

“There are other Goldilocks zones. Moons can experience such strong tidal tugs that the heat released by internal friction can sustain liquid water.”

This was the second major eye-opener for me: “Our environment is full of chemical disequilibrium […] there are reactions just waiting to happen. […] The metabolisms that drive life accelerate reactions in the environment, releasing energy faster than would have occurred without life” (p. 144). Hand takes a leaf out of Nick Lane’s book The Vital Question (which, shame on me, I still have not read) when he enthusiastically concludes that “the why of life is metabolism” (p. 146), offering the universe a pathway to increase entropy faster. These are remarkable ideas that give a whole new meaning to philosophical questions on the meaning of life.

The third and final eye-opener concerns the need for a catalytic surface, which is where Hand circles back to oceanographic exploration here on Earth, a recurrent theme in this book. When the submarine Alvin discovered hydrothermal vents in 1977 and found them teeming with life, these quickly became a popular alternative explanation to warm tidal pools as a place where life could have started. These so-called black smokers are powered by magma rising to the surface at mid-ocean ridges, jetting out superheated water of over 400 °C. Though volcanism and tectonics are, or sometimes were, common processes on many solar system bodies, there is another option. Alkaline vents, first discovered in 2000 at the Lost City hydrothermal field, are powered by exothermic (energy-releasing) reactions between water and mineral-rich rock, heating water to a more gentle 70–100 °C. All these need are the right rocks with cracks in them so water can percolate down.

“In addition to hydrothermal vents, alkaline vents are another place where life might have started. All these need are the right type of rock with cracks in them so water can percolate down, no plate tectonics needed.”

Hand raises many other interesting questions towards the end of the book, of which I will mention just three. One, life’s metabolic reactions require so-called oxidants, oxygen being “the most glorious of oxidant” (p. 162), but how would these get down into subsurface oceans? Two, how contingent or convergent is the evolution of life’s biochemistry? Carbon is a suitable building material for life as it is “hands down the best team player on the periodic table” (p. 212). But to these options, or can we sketch a periodic table of life with other, weirder possibilities? And three, how should we seek for signs of life? What makes a good biosignature? This is discussed far more in-depth in Life in the Cosmos, but Hand considers three types of evidence.

Alien Oceans limits itself to oceans in our solar system, not touching on the topic of exoplanetary oceans. Given this is not Hand’s expertise, that is reasonable. He also glosses over the question of what aliens might look like, though he speculates on the likelihood of intelligent life in ice-covered subsurface oceans. Even without these topics, Alien Oceans is information-dense, requiring me to make a summary, and then a summary of that summary while preparing this review. Nevertheless, it is an intellectually very rewarding book and the many analogies make it accessible. I enjoyed it as a follow-up to Ocean Worlds but it is a fine standalone book. Terribly fascinating, Alien Oceans makes a convincing case for exploring the moons in our solar system in the search for extraterrestrial life.

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

Alien Oceans

Other recommended books mentioned in this review:

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Rivers and oceans are easily neglected when it comes to pollution. Out of sight, out of mind and all that. Except that the oceans do not forget. Of all the water pollution problems, oxygen loss is probably one of the more abstract ones. Even the words used to describe it, hypoxia and anoxia, will be meaningless to those without a background in biology. In Dead Zones, marine scientist and microbiologist David L. Kirchman provides a general introduction to the problem of oxygen loss and why it matters.

Dead Zones: The Loss of Oxygen from Rivers, Lakes, Seas, and the Ocean, written by David L. Kirchman, published by Oxford University Press in April 2021 (hardback, 224 pages)

I thought you could not tell me anything new on this topic. After all, for my PhD, I spent five years in Finland studying how fish behaviour in the Baltic Sea is affected by eutrophication, the pollution caused by excess nutrients. The Baltic is one of several badly affected water bodies in the world due to the large land area that drains into it and the narrow connection with the North Sea. However, my studies focused on decreased underwater visibility due to algal blooms rather than oxygen loss. Dead Zones was thus a welcome surprise and refresher, showing that even I had only an incomplete picture of the problem.

So what are dead zones? They are areas of fresh or marine water that have low (hypoxia) or virtually no (anoxia) dissolved oxygen. As Kirchman clarifies in his prologue, the term is a bit dramatic. It does not mean that the whole water column is affected, often it is limited to the bottom layer. And they are not always completely dead, some organisms actually thrive here. But many creatures are sensitive to oxygen loss, leading to slower growth, fewer offspring, and poorer health. In extreme cases, it leads to the death of fish and bottom-dwelling invertebrates, reduced biodiversity, and reshuffled food webs.

Dead zones vary in size through time, influenced by weather and currents. But since about the 1950s, they have been steadily growing both in size and number, and we know the cause. Fed by excess nutrients, algae bloom. When they die, the bacteria decomposing them use up oxygen quicker than it can be refreshed. But before we get to this point in our understanding, the first half of the book takes the circuitous route through the history of their discovery.

“[Dead zones] were a natural occurrence in the past, but the frequency and severity have increased, and it all centres on roughly 1950.”

Some of the first dead zones that were widely noticed were the Great Stinks. Not that long ago, many rivers running through bustling cities in Europe and the US received large loads of untreated sewage. The resulting bacterial feast would rapidly consume all the oxygen and then switch to sulfate metabolism, releasing hydrogen sulfide with its characteristic smell of rotten eggs. Wastewater treatment facilities brought this problem under control, with rivers recovering and fish returning.

Much harder to notice were the dead zones developing in coastal areas, such as the Gulf of Mexico or Chesapeake Bay, or inland seas, such as the Black Sea or the Baltic Sea. Kirchman takes you through their discovery in the 1980s and the research by Nancy Rabalais and others to address the question whether they have always been there? The answer required the meticulous collection of long time series of oxygen measurements and the study of sediment cores that record past oxygen levels. The conclusion is that, yes, they were a natural occurrence in the past, but the frequency and severity have increased, and it all centres on roughly 1950. How so? More nutrients, specifically nitrogen and phosphorus. Where did they come from? Artificial fertiliser used in agriculture. As discussed here, there have been naysayers, both in scientific circles and amongst farmers and industry, but the evidence is pretty convincing by now.

Although Kirchman does not explicitly mention it, the 1950s marks a transition period dubbed the Great Acceleration during which our impact on the environment boomed. And the increase in nitrogen and phosphorus release is one of many indicators used by scientists to define the start of the Anthropocene. Two key figures Kirchman introduces here are Fritz Haber and Karl Bosch. The former developed a process to cheaply and efficiently fixate nitrogen, the latter scaled it up for the industrial production of explosives and artificial fertiliser. The Haber–Bosch process was one factor facilitating the human population explosion driving the Great Acceleration. As Kirchman mentions, “Depending on your diet, about half of the nitrogen in your body came from a factory using the Haber–Bosch process” (p. 96), and Vaclav Smil is quoted as writing that, without it, Earth would probably have only half the human population it has now.

“[…] these problems have been […] difficult to tackle. One factor is the inherent complexity of the system. […] There is no one-size-fits-all solution.”

Having arrived at the status quo, the second half of Dead Zones explains why these problems have been so difficult to tackle. One factor is the inherent complexity of the system. Which nutrient is the limiting one runs the full gamut from nitrogen in marine waters (mostly) to phosphorus in lakes, and sometimes neither. There is no one-size-fits-all solution. Similarly, as Kirchman explains, fish kills are not a problem suitable for a bumper sticker slogan to rally behind: “Dead Zones Kill Fish and Fishery Jobs” (p. 128). The reality is more nuanced. Oxygen depletion can, for example, boost fish landings when fish flee hypoxic zones and become easier to catch. And this leads to the second factor: all these complexities make it very easy for those who stand to lose from tougher environmental regulations to call for more research, and for legislators to hesitate to implement anything. However, as Kirchman points out: “[…] we cannot ignore dead zones just because the effect of hypoxia is complex” (p. 133). To that end, he offers a range of solutions, including things that you, the reader, can do.

Dissolved oxygen levels in water was never going to win the prize for the sexiest topic. Given this inherent handicap, Kirchman’s conversational tone makes Dead Zones nicely accessible. However, I do feel that the overall structure and clarity suffer somewhat, although I cannot quite put my finger on the why. The narrative ricochets between different topics and some things are only touched upon (e.g. the rise of jellyfish, or the release of neurotoxins during certain algal blooms). I did enjoy the historical sketches, they are Kirchman’s forte. At only 172 pages, this book is not a thorough overview but more a general introduction. Since these topics are normally discussed in scientific journals, reports, academic monographs, and edited collections, it is an introduction that is long overdue.

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

Dead Zones

Other recommended books mentioned in this review:

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What I am about to write is probably going to upset many people, but… I am growing frustrated with the narrative of much of the environmental movement. Taking to the streets to protest and demand change, to “do something!”, is all fine and dandy, but it is also a bit hypocritical. It fosters a narrative in which the onus is always on others and it begs the counter-question: “what are you willing to give up?”. That is the hard question.

There, I said it. You have the option to stop reading now.

In all seriousness, if we want to avert dangerous climate change or allow forests to recover from deforestation, how much change is enough? How much are we allowed to consume? Planetary Accounting will not offer you final prescriptive answers, but it is an important first step in quantifying per capita quota for what each of us can consume and pollute without it costing the planet.

Planetary Accounting: Quantifying How to Live Within Planetary Limits at Different Scales of Human Activity, written by Kate Meyer and Peter Newman, published by Springer in March 2020 (hardback, 290 pages)

This book follows on perfectly from Kallis’s Limits that I just reviewed, which urged for a culture of self-limitation. The immediate follow-up question then is: how much? In Planetary Accounting, sustainability scientists Kate Meyer and Peter Newman take the planetary boundaries framework as their starting point and translate it into planetary quotas. If the former can be likened to a patient’s diagnosis, the latter can be interpreted as the doctor’s prescriptions: here is the amount and direction of change needed.

In case you are not yet familiar with it, the planetary boundaries framework was developed by Johan Rockström and colleagues and presented in a 2009 Nature paper, followed by a book for a general audience in 2014, and further refinements proposed in a 2015 Science paper. It is an Earth systems science framework that demarcates a “safe operating space for humanity” by identifying nine planetary processes and systems with their boundary values. Think climate change, biodiversity loss, or ozone depletion. For several of these, we have crossed the limit and are collectively pushing our environment towards a new state that is likely to be a lot less friendly to human life. A case is even being made that we have entered a new geological epoch, the Anthropocene.

You might ask why it matters that we emit more nitrogen and phosphorus into our environment than we should, or are seeing species extinction rates far above background values. Surely, our world always changes and is not a museum piece. Consider the following, I think very interesting, argument. Some authors propose that it took the stable climatic conditions of the Holocene for civilization to take off. Not because climate drove civilization—humanity was rearing to go—but because we needed a stable window of opportunity. Meyer & Newman mention Cook’s A Brief History of the Human Race, but I came across this same argument in Dartnell’s Origins where he suggested that there may have been earlier attempts at migrating out of Africa or developing agricultural civilizations, that simply fizzled out before taking off because environmental conditions were unfavourable. Rockström and colleagues argue that the state of the planet during the Holocene is the only one we know of in which settled societies can thrive. Whether we can in other environmental states is unknown, nor do we know what new balance the Anthropocene will reach. So, how lucky, really, are we feeling?

“it took the stable climatic conditions of the Holocene for civilization to take off. […] Whether we can [thrive] in other environmental states is unknown […] So, how lucky, really, are we feeling?”

This introduction is accompanied by a very capable routing of the arguments of climate change denialists and a brief exploration of other environmental impact assessment frameworks before Meyer & Newman turn to the limits of the planetary boundaries framework. One issue is that it describes the problem, but does not prescribe solutions. Some translation is needed and to that end, Meyer & Newman here propose the planetary accounting framework.

The bulk of the book describes this framework and develops quotas for each of the nine planetary boundaries, though it should be noted that readers might have to turn to supporting publications, including Meyer’s PhD thesis, for more details. What this exercise reveals is interesting. Four planetary boundaries have been exceeded, three not yet, and for two we lack information. The planetary quotas calculated here show we exceed seven, are at the limit of one and lack information for the last. If that seems confusing, remember that boundaries describe the state of the planet and quotas our annual impact. Some boundaries will be breached soon if we maintain current rates.

To illustrate this with an example. For climate change, one planetary boundary is an atmospheric carbon dioxide concentration of 350 ppm (parts per million), which has been exceeded. The corresponding quota is based on CO₂ emissions, expressed in gigatonnes. To meet the target of the IPCC climate change scenario that the authors have selected (limit global warming to +1.5 °C by 2100) we should change our emissions from the current +36 to -12 GtCO₂/year. This is an example where we should not just reverse direction (i.e. emit less), we should be actively removing atmospheric CO₂. Deriving quotas for all boundaries is not necessarily straightforward and Meyer & Newman have drawn on the knowledge of a large body of specialists when developing the planetary accounting framework, with caveats, justifications, and assumptions described here.

“[The planetary boundaries framework] describes the problem, but does not prescribe solutions. Some translation is needed and to that end, Meyer & Newman here propose the planetary accounting framework.”

Each chapter also gives suggestions on how these quotas can be achieved at different levels (from individuals to nations) and in different sectors (communities, governments, and businesses). They call their approach poly-scalar. Although this is a first step in translating planetary boundaries to something more actionable, you will notice that this is still several steps away from usable advice. The authors acknowledge that more work is needed, that there are different ways to achieve these quotas, that the quotas are moving targets subject to revision, and that there will be a lot of political and ethical horse-trading when it comes to deciding who has to sacrifice what (especially in the developed vs. developing world). In short, they have laid out the total amount of change needed but how we are going to achieve this is yet to be decided.

I have two points of criticism. First, with the book itself. Though accessibly written, it suffers noticeably from typos and spelling errors that should have been picked out in the editorial stage. Furthermore, seeing the importance of the subject matter, the book is exorbitantly priced, probably putting it out of reach for many readers. I recommend you also have a good look at the website of The Planetary Accounting Network, the non-profit that Kate Meyer founded after completing her PhD.

My second point of criticism is with the planetary accounting framework, which has its limitations. There is no mention here of non-renewable resources: all the ores and other minerals we extract from the planet’s crust, many of which, such as rare metals, are vital to the technological solutions we envision will help us address environmental problems. Whether their framework can be expanded and adjusted to account for these is questionable, seeing such resources are finite. Furthermore, Meyer & Newman are conspicuously silent about overpopulation, although occasionally mentioning that quota sizes will depend on future population growth. I know that I am starting to sound like a stuck record, but should there be a population quota? Depending on living standards plugged into your equations, some authors have tentatively concluded that 3 billion is a more sustainable limit and that we cannot justify having more than one child.

Of course, it would be unreasonable of me to expect their framework to be a cure-all—they acknowledge it is not “one supersystem to solve everything”. Keeping that in mind, Planetary Accounting is a first step in translating the planetary boundaries to something more actionable, and Meyer & Newman provide a valuable roadmap that I expect will be widely welcomed.

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

Planetary Accounting

Other recommended books mentioned in this review:

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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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In Algae We Trust. That might just as well have been the subtitle of this book. In Slime (published in the UK as Bloom, but I read the US version), author Ruth Kassinger writes of the many fundamental, often eye-opening roles that algae play in our ecosystems. But she also travels around the world to talk to farmers, scientists, and inventors. From food to plastics to fuel, entrepreneurs are discovering that these little green powerhouses hold immense biotechnological potential.

Slime: How Algae Created Us, Plague Us, and Just Might Save Us, written by Ruth Kassinger, published in the USA by Houghton Mifflin Harcourt in June 2019 (hardback, 320 pages)

From the above, you will have already gathered that this book covers a myriad of topics. Kassinger has helpfully grouped her 27 short and very readable chapters into four sections. These deal with evolution and early life, algae as food, algae as fuel and feedstock, and the role of algae in a changing climate. Kassinger writes in a casual style without dumbing things down, and when she cracks a joke, they are actually clever. The truth is, she does not have to work hard to sell the book to her reader – it contains so many eye-opening facts and inspiring stories of biotech initiatives that it sells itself. That, and there are a handful of lovely illustrations by Shanthi Chandrasekar.

I took great interest in the first section on early life, even though, as an evolutionary biologist, I am familiar with many details. For example, the first fossils (stromatolites) left by cyanobacteria (blue-green algae); the Great Oxygenation Event and the rusting of Earth’s iron reserves; or the first instance of endosymbiosis that turned a strain of cyanobacteria into chloroplasts, the photosynthesising powerhouses found in plant cells. All of these amazing events have been covered extensively elsewhere, though Kassinger relays them with great ease. Amazingly, cyanobacteria have also been implicated in causing the Huronian Glaciation that saw the planet frozen solid between approximately 2.4 to 2.1 billion years ago. (Actually, I did know this from reviewing The Oceans, but I had forgotten about it.)

“Amazingly, cyanobacteria have also been implicated in causing the Huronian Glaciation that saw the planet frozen solid between approximately 2.4 to 2.1 billion years ago.”

The other three sections of the book contained much that was new to me. Archaeologists argue that humans, in pursuit of seafood, stuck to coastlines as they migrated around the planet, and Kassinger highlights that it might very well have been the nutrition found in algae that stimulated brain expansion during our evolution. She explores the importance of algae in Japanese cuisine and visits a South-Korean algae farm, as this country has become the world’s leading exporter. Interestingly, there is also a strong tradition in Wales to collect algae as a cooking ingredient.

What I really appreciated here was Kassinger’s even-handedness. So, while she visits a wild-seaweed harvester who tries to run a business in harmony with nature, she also takes a look at a commercial aquaculture operation. And while she highlights the fantastical nutritional value of algae, she is sceptical of overblown claims by producers and cautious of supposed health benefits of, for example, omega-3 oils. And she is outright scathing – deservedly so – of wellness gurus who ignore scientific evidence to the contrary by claiming that carrageenan, a polysaccharide compound in algae, is unsafe for consumption.

“What I really appreciated here was Kassinger’s even-handedness […] while she highlights the fantastical nutritional value of algae, she is sceptical of overblown claims by producers […]”

Beyond food, algae can reduce the need for antibiotics in animal husbandry, be used as agricultural fertilizer, or – excitingly – be turned into oil to make plastics or fuel. It was a chance visit to a startup biofuel company that got Kassinger started on this book in the first place, so she spends quite a bit of time going into the particulars of oil. Although biofuel has gotten a bad reputation for the land and water requirements of crops such as corn, algae culture does not need premium agricultural land or freshwater. As with all these novel applications, a lot of research and development is still needed to optimise production processes, though recent gene-editing tools such as CRISPR could greatly help.

It is hard not to get starry-eyed about the possibilities, but I think that Kassinger gives a balanced account. For instance, her explanation of why electric cars are not necessarily better for the environment shows an author who acknowledges subtleties and avoids hype. (After all, it depends on where the energy came from that you charge their batteries with.) But even taking a cautious stance, algae do seem to hold great potential for producing the different kinds of fuel needed by cars, aeroplanes, and ships. As she highlights, it is unfortunate that the fracking boom has knocked the bottom out of oil prices, bankrupting some promising startup ventures working on algae fuel. Others have shifted their business to making oils used in the foods and cosmetics industry, including alternatives to the dreaded palm oil.

“It is hard not to get starry-eyed about the possibilities, but […] algae do seem to hold great potential for producing the different kinds of fuel needed by cars, aeroplanes, and ships”

In the book’s final section Kassinger considers algae in coral reefs and the threat of climate change, algae naturally mopping up excess nitrogen and phosphorus, the problem of harmful algal blooms, and the possible role of algae in geoengineering to draw down atmospheric carbon dioxide.

Kassinger is an enthusiastic yet even-handed cheerleader for algae. Despite the huge range of topics covered her book is well organised. What really makes it a joy to read are her deft explanations – whether it is the difference between pro- and prebiotics, or the finer details of oil production. Even when she writes on a topic I am more familiar with, such as the atmospheric chemistry behind the Great Oxygenation Event, she shows an enviable knack for writing plainly. An ode to pond scum, this book is an eye-opener that ensures you will never look at algae the same way again. For a more recent take on this subject, readers might also want to check out The Seaweed Revolution that was published four years later in 2023.

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

Slime / Bloom hardback, ebook or audio CD

Other recommended books mentioned in this review:

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