This is the fifth instalment in what can unofficially be dubbed the 25 Discoveries series by palaeontologist and geologist Donald R. Prothero. After four previous books on fossils, rocks, dinosaurs, and evolution—I reviewed the last three (mostly) positively—Prothero now turns to palaeoclimatology. A chronology with character, this book takes the reader through 4.5 billion years (Ga) of Earth’s changing climate and its impact on life, while explaining how we know what we know.

The Story of Earth’s Climate in 25 Discoveries: How Scientists Found the Connections Between Climate and Life, written by Donald R. Prothero, published by Columbia University Press in March 2024 (hardback, 466 pages)

This book flows from Prothero’s experience teaching about Earth systems and climate change. After browsing some of the books I have on the subject, I noticed that the structure deviates somewhat from others. Whereas Ruddiman’s Earth’s Climate focuses on the underlying concepts, and Summerhayes’s Paleoclimatology follows a 200-year chronology of the discipline of palaeoclimatology, Prothero’s approach hews much closer to Bender’s primer Paleoclimate in following a strict chronology of Earth’s climate. More than a primer, though, it is generously padded out with relevant material to make for a chunky book.

One consequence of the coursework on which Prothero draws is that he starts with four cosmology- and astronomy-themed chapters that he admits are not strictly about climate, such as the formation of stars, solar systems, and our sun and moon. With the literal substrate of our planet in place, there follows a 4.5-Ga-chronology in 21 chapters. For those who have read other popular works on this topic, there are familiar periods such the Huronian Snowball Earth episodes 2.5–2.2 Ga ago, the ice-age worlds of the Carboniferous 359–299 million years (Ma) ago when elevated oxygen levels allowed insects to grow nightmarishly large and a significant chunk of the world’s fossil fuel reserves were formed, or the proverbial greenhouse of the dinosaurs 145–66 Ma ago (this referencing Prothero’s book on the Cretaceous hothouse climate). But there is also attention for events that have rarely or only recently been discussed in popular works. An example of the former is the Carnian Pluvial episode, a strange 2 Ma interval of high humidity and extreme rainfall 234–232 Ma ago. An example of the latter is the Paleocene-Eocene Thermal Maximum ~55.8 Ma ago when atmospheric carbon dioxide levels and temperatures spiked. There is increasing interest in this interval as a past analogue of what is in store for our near future if humans do not rein in greenhouse gas emissions.

“there is […] attention for [climatic] events that have rarely or only recently been discussed in popular works.”

An important goal for Prothero is to explain how we know what we know so that readers understand how the climate works and why it changes. As such, much attention is given to the numerous lines of evidence on which palaeoclimatology draws. The fossils that show Greenland was once carpeted by lush forests while Antarctica was the stomping ground of dinosaurs. The stratigraphical evidence that tells stories of past ice ages by way of dropstones, erratics, and glacial till deposits. The fossil riverbeds in today’s deserts. The cyclical climate patterns revealed by repeating strata with obscure names such as cyclothems and varves. The palaeoclimatological archives contained in deep-sea sediment cores and Arctic ice cores. The numerous lines of evidence for plate tectonics. The geochemical evidence showing past changes in the composition of the atmosphere. The importance of microfossils, etc., etc. Prothero provides plenty of background material for the reader not schooled in geology and palaeontology. The only notable omission here is tree rings that are only mentioned in passing; unfortunate, as the story of dendrochronology is fascinating.

A secondary aim of this book is to show how life and climate have interacted with each other. Though some examples are given of life shaping the climate (e.g. the oxygenation of our atmosphere), the interactions mostly run the other way with Prothero prominently discussing the big five mass extinctions. These often resulted from rapid changes to Earth’s oceans and atmosphere, with episodes of massive volcanism frequently the likely kill switch. Wait, all of them? Some readers might be surprised that, when it comes to the end-Cretaceous mass extinction, Prothero is critical of the impact of the impact. Once you take a step back from the non-avian dinosaurs and note how other terrestrial groups were not particularly affected while the picture for marine groups is mixed, the story becomes more complicated. During his career, Prothero has been witness to the long and often lively debate over the role played by the massive volcanism that laid down the Deccan Traps in today’s India. In his opinion, this idea is less fringe than some would have it. “If the impact had any real effect at all, it was the coup de grâce for already terrible conditions in the Late Cretaceous” (p. 287).

“An important goal for Prothero is to explain how we know what we know […] As such, much attention is given to the numerous lines of evidence on which palaeoclimatology draws.”

Compared to the previous three books in the 25 Discoveries series that I reviewed, the role of the discoverers takes more of a backseat this time. The clue seems to be in the book’s subtitle: we have moved from “the people who found/solved them” to How Scientists Found the Connections Between Climate and Life. By now, there is some unavoidable repetition: researchers such as Alfred Wegener or James Croll’s underappreciated contribution to the ideas of Milutin Milankovic have featured before. Beyond that, the coverage is a bit spotty. There are, for instance, nice biographical sketches of geologist Alfred Fischer, who studied cyclical climate patterns, and palaeontologist Mary Dawson, who led Arctic fieldwork that taught us more about the climate of the lower Eocene, 56–48 Ma ago. Various others, however, get little more than a brief mention.

This brings me to some criticism. The foremost complaint I have is that, though I approve of Prothero’s desire to include material on the formation of stars and planets, this should have been condensed into a single chapter. I am not convinced we needed four chapters that touch on astronomical arcana such as the Fermi paradox, Drake equation, Kardashev scale, or the Hertzsprung–Russell diagram. This space could have been used to include more biographical sketches, or to flesh out e.g. the final chapter where he now rather hurriedly tries to convince the reader why current climate change has the human fingerprint all over it. I think the balance of the rest of the book is good: coverage of a large topic such as the impact of climate on human civilizations is appropriately limited given the vast scope of time considered here. I like that Prothero inserts some personal opinion while mostly managing to keep his tangents contained (there is e.g. only a brief mention of his hobby horse, the Toba eruption). Occasionally he slips a bit, such as a three-page listing of moon deities and other pre-scientific ideas, a section on how Carl Sagan was shunned and ridiculed for his science communication efforts, or a long list of unexpected discoveries to come out of basic or exploratory research (and Prothero’s ire at such research not being valued). Beyond this, my other gripes are minor nitpicks. There are some conversion errors in metrics and he does not always credit (palaeo)artists in figure legends (for instance notably omitting Charles R. Knight on p. 263). Lastly, as before, quite a few figures were designed with colour reproduction in mind and do not really work when printed in greyscale, though I hasten to add that several others have been suitably redrawn.

Above criticism notwithstanding, I think Prothero succeeds in educating the reader about Earth’s past climate. The book is informative and quite long but remains accessible and interesting. The attention given to mass extinctions seems appropriate given the close link to climatic changes. Prothero is not afraid to insert personal opinions in places, making this a palaeoclimatology chronology with character.

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

The Story of Earth’s Climate in 25 Discoveries

Other recommended books mentioned in this review:

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Many advances in the earth sciences have come from one particular feat of technology and engineering: deep-sea drilling. Or to be more precise, it is the sediment cores thus extracted from the seafloor that have offered a wealth of information. In Mysteries of the Deep, retired geologist James Lawrence Powell gives a very readable whistlestop tour of the many remarkable insights these drilling expeditions have given us. In the process, he provides a microcosm of how science advances and how scientists change their minds, or sometimes fail to, in the face of new evidence.

Mysteries of the Deep: How Seafloor Drilling Expeditions Revolutionized Our Understanding of Earth History, written by James Lawrence Powell, published by MIT Press in February 2024 (hardback, 276 pages)

As with other things oceanographic, we can trace the origins of deep-sea drilling to the Challenger expedition. Next to many extraordinary animals, it collected sediment samples using a hollow tube that would plunge into the seabed. In various chapters, Powell traces how successive expeditions improved on this technique and retrieved longer sediment cores. A first attempt in 1961 at drilling through sediment to reach the underlying mantle rock^[1], project Mohole, succeeded technically but subsequently floundered bureaucratically. It did lead to the collaborative partnership JOIDES (Joint Oceanographic Institutions for Deep Earth Sampling) in 1964 in which several universities teamed up and successfully obtained funding from the National Science Foundation. This was the start of a series of research projects that have been ongoing for the last six decades. Powell provides a fair amount of detail on the first project and the engineering challenges and solutions but has relegated information on later vessels and programmes to a brief 2-page appendix. There are no doubt stories left untold here. Instead, the focus is squarely on the fruits of all this labour. What has deep-sea drilling ever done for us? Actually, a surprising amount!

Anyone familiar with the history of geology will not be surprised that several chapters deal with continental drift and plate tectonics. This decades-long saga, examined at length in e.g. The Tectonic Plates are Moving!, saw independent lines of evidence pile up, even as the idea continued to be staunchly resisted. Powell gives a concise overview and highlights the contributions made by deep-sea drilling. For instance, drilling at increasing distance from the Mid-Atlantic Ridge revealed progressively older rocks, consistent with the idea of seafloor spreading. It also vindicated Marie Tharp’s hunch, based on her and Bruce Heezen’s meticulous mapping of the Atlantic seafloor, that the ridge was a rift valley where two plates were separating.

“Anyone familiar with the history of geology will not be surprised that several chapters deal with continental drift and plate tectonics [but] deep-sea drilling furthermore contributed to other, less expected topics”

Beyond the obvious, deep-sea drilling furthermore contributed to other, less expected topics. For example, in recent geologic history, the Mediterranean Sea became cut off from the Atlantic and dried up, an episode known as the Messinian Salinity Crisis. Deep-sea drilling found large deposits of evaporite salt that were left behind, as well as very deeply eroded river mouths that were later backfilled with newer marine sediment. Other drilling expeditions have found evidence of , so-called intraterrestrials. Drilling has delivered insights on palaeoclimatology, with one of the nine holes drilled in 1987 during Leg 113 of the Ocean Drilling Program becoming “a shining example of the value of scientific ocean drilling” (p. 210), spawning hundreds of scientific papers. It provided crucial evidence for a period of intense runaway climate change known as the Paleocene-Eocene Thermal Maximum 56 million years ago where average global temperatures soared by approximately 7°C. Deep-sea drilling has even shed light on human evolution. Cores extracted off the coast of East and West Africa show that in the last 3 million years there were periods where the climate rapidly alternated between wet and dry conditions. These periods coincided with new hominin species appearing in the fossil record. Palaeoanthropologist Rick Potts thinks the ability to adapt to extreme climate fluctuations was strongly selected for, dubbing his idea “survival of the adaptable”. Walking upright and tool use are traits that would have helped in this regard.

A noticeable second component in this book is Powell’s interest in science history and the progression of ideas. His previously reviewed Four Revolutions in the Earth Sciences explicitly examined four such episodes and it makes a welcome return here. Next to the abovementioned history of plate tectonics, Powell gratefully draws on the 1986 book by the Imbries to recount the discovery of the Pleistocene Ice Ages. Though the name of Louis Agassiz is usually attached to this, it was more of a relay race. In the face of almost wholesale rejection, you can trace a concatenation of scholars (there is a new collective noun for you) who defended the idea before it reached Agassiz in 1834. Powell also highlights examples of scientists changing their minds. Darwin himself did not notice anything out of the ordinary when visiting glacial deposits in Wales in 1831, but upon a second visit in 1842 thought the evidence could not be clearer. “Even the greatest minds cannot think the unthinkable” (p. 131). Similarly, geologist J. Tuzo Wilson went from opposing continental drift in 1960 to supporting it in 1961 after reading about a novel hypothesis for the formation of the chain of volcanic islands of Hawai’i. Rather than a large volcanic fissure moving along a static seafloor and periodically extruding islands (for which no mechanism was proposed), it was actually the seafloor that moved over a volcanic hotspot.

“A noticeable second component in this book is Powell’s interest in science history and the progression of ideas [which] makes a welcome return here.”

What makes this book a pleasure to read is the conciseness of the chapters, which never exceed 20 pages; no topic overstays its welcome. Additionally, Powell makes good use of (historical) illustrations to visually explain concepts, as well as show what scientists thought at certain points in time. There are one or two chapters that can get quite technical. Although I am familiar with Milankovitch cycles (another topic where Powell adds a nice science history angle), the chapter discussing the subsequent development of astrochronology and cyclostratigraphy was a challenging read. Overall, at least some familiarity with earth sciences will be beneficial to the reader.

Whereas the related topic of ice core drilling has been the subject of at least two popular books in the last ten years, there has to my knowledge not been a popular book on deep-sea drilling since Kenneth Hsü’s 1992 book Challenger at Sea. With Mysteries of the Deep, Powell delivers that book: a fascinating and accessible whistlestop tour of what international collaborative science can achieve. As mentioned in his final chapter, though the current International Ocean Discovery Program is scheduled to conclude next month in September 2024, the earth science community is busy planning its follow-up. There are many more questions that we did not even know we had before deep-sea drilling.

1. ↑ As I was finalising this review, Science reported the deepest core retrieved from the mantle yet, 1268 m deep into the mantle, during Leg 399 of the International Ocean Drilling Project.

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

Powell’s Mysteries of the Deep

Other recommended books mentioned in this review:

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Following on from this 2022 book Travels with Trilobites, fossil collector and trilobite enthusiast Andy Secher returns with The Trilobite Collector’s Guide. Leaning fully into his background as a long-time editor of hard rock magazine Hit Parader, he here presents 52 chapters with top 10 lists that present a medley of trilobite facts and factoids. As before, this book is chock-a-block with many previously unseen colour photos of these fossilised arthropods, showcasing their tremendous morphological variation. In the spirit of this book, here are my top 10 observations on The Trilobite Collector’s Guide.

The Trilobite Collector’s Guide, written by Andy Secher, published by Columbia University Press in February 2024 (hardback, 453 pages)

1. Let others sing your praises
Travels with Trilobites featured three forewords by notable palaeontologists. For this book, Secher managed to snare no less than trilobite mastermind Richard J. Fortey, the former head of fossil arthropod research at the Natural History Museum, London, and Melanie J. Hopkins, curator of fossil invertebrates at the American Museum of Natural History, New York (where Secher co-edits their trilobite website). Hopkins provides her own top 10 reasons why you should read this book and nicely observes that “to be a truly great collector, however, is also to be an ambassador” (p. xiii). That describes Secher to a T.

2. Mind the collectors
For those who have bought Secher’s previous book, rest assured that this one has the same dimensions and sports the same font on the cover. The two make a fine pair on your bookshelf.

3. Abundant alliteration and purple prose
More so than in his previous book, Secher leans heavily on alliteration. Scanning the table of contents, alliteration abounds: “10 Significant Silurian Trilobite Localities”, “10 Eminently Elegant Trilobites”, “10 Pertinent Preparation Steps”, “10 Extravagantly Expensive Trilobites” etc. etc. In the text, too, Secher will not resist talking of “fossiliferous fascination” (p. v), “the trilobite line’s tenacious trek through time” (p. 89), websites such as eBay encouraging “auction action” (p. 307), and of “callous-causing hours spent breaking rock” (p. 417). He can occasionally go overboard on the purple prose, e.g. by describing collectors who are not intimidated by large numbers and controversial theories as people “willing to stare the great abyss of time squarely in its fanciful face” while they deal with “cerebrally challenging topics [and] scientifically scintillating theories” (p. 127). Secher is nothing if not enthusiastic, but it might not be everyone’s calcareous cup of trilobite tea.

4. Location, location, location
Something that I have only been slow to realise is that much of what we have learned in palaeontology is intimately bound to very specific locations that provide a window into a very specific period in time. For each geologic period, he features 10 notable locations all around the world (for me, the beautiful Ordovician fossils found around St. Petersburg, Russia stand out). Additional chapters highlight spectacular fossils from trilobite-hotbeds such as Morocco or Utah, or focus on famous quarries such as the Walcott/Rust quarry and Rochester Shale in New York State, or outcrops in Dudley, England.

5. No subject left behind
Next to the obvious top 10s with superlatives (the oldest, youngest, rarest, biggest, and most expensive fossils), the 52 chapters leave virtually no topic untouched. There are chapters on morphological aspects (enrollment, eyes, spines, disarticulated fragments, and soft tissue preservation), some very interesting chapters on practical aspects of the hobby (with top 10 tips on collecting, curating, preparing, and valuing your fossils), and chapters offering mini-reviews of the top 10 best books, websites, museums, and fossil shows. It feels like he has taken the long and scattershot “Trilobite Thoughts and Observations” chapter in Travels with Trilobites and fleshed it out for this book.

6. Is more always better?
Tying in with the above observation, whether more is better is a fair question to ask. At 453 pages this is a long book and some chapters struggle to set themselves apart: is there really any difference between “10 Legendary Trilobites”, “10 Strikingly Strange Trilobites”, and “10 Deserving-of-Mention Trilobites”? Chapter 44, “10 Trilobite Orders”, which lists 10 names for each order, feels like filler and could have offered a far more interesting summary of what sets each order apart from the other.

7. Lest we forget the science
Though collector interests take the lead in this book, there are sporadic injections of interesting science here. A recurrent theme is how similar or even identical trilobite species showing up in outcrops on different continents is a key observation in support of plate tectonics. Another theme is the fossilised evidence of behaviour such as enrollment, traces of predation, the famous conga-line of trilobites on the march, and so-called mass mortality plates with lots of fossils heaped on top of each other, which could have resulted from moulting or mating assemblages.

8. What mad medley
As with his previous book, the aim has been to produce a “package of pure Paleozoic entertainment” (p. 5). Secher leans heavily on fast-paced, bite-size, listicle-style content. The topics are thoroughly mixed up and he bounces between them in no particular order, making the book more suitable for dipping into than reading in long sittings.

9. Opportunities missed
Overall I feel Secher has done a good job of presenting an accessible and entertaining collection of trilobite-themed facts but, in my opinion, there are some minor opportunities that he missed. I would have liked to see a better overview of commonly found body parts and fragments in the chapter “10 Tantalizing Trilobite Teasers”. Also, many fossils are found as moults and Secher repeatedly mentions these can be recognized because they miss their free cheeks. I still do not know what that looks like in practice so some comparison photos would have been helpful. As before, the book features no references and thus has many generic and unverifiable statements about what scientists think or have disagreed about. At the other end, there are several scientific conventions that he does not explain: for instance, what do n. sp. or cf. in species names stand for? (I was unfamiliar with the latter.) And how does the species concept work for fossils?

10. Thoughts on the photography
Finally, a word about the photography as I was rather critical of this in my review of Travels with Trilobites. He has improved on it here. Somewhat. In his introduction, Secher clarifies that he is indeed the photographer. Not happy with the photos taken by a professional, he gave it a shot himself, “but I fully recognize my limitations behind the lens” (p. 7). This time around there has fortunately been no embarrassing inclusion of pixelated photos. Though many photos are nice and sharp, many are equally still notably grainy (for example the Proceratocephala specimen on p. 68) or partially out of focus. It is telling that the few photos contributed by others are noticeably better. Seeing that this is a book to be enjoyed for its visual content, I would have implored Secher to hire a professional photographer had I been his editor.

Overall, The Trilobite Collector’s Guide boils over with Secher’s enthusiasm for trilobites and it is, I must admit, rather infectious. I have been eyeing up several further books after reading his top 10 recommendations, and thus, incidentally, discovered that a second volume of the rather legendary The Back to the Past Museum Guide to Trilobites was published a few months ago. If you enjoyed his previous book, then buying this one is a no-brainer, especially given the huge amount of new photography. For those new to Secher or already in possession of other trilobite books I am a little bit more reserved in my recommendation. Given the book’s idiosyncratic format of top-10 lists, occasionally iffy photography, and rather hefty price tag of £50/$59.95 at the time of publication, you may first want to leaf through a copy in a bookshop if you have the opportunity.

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

The Trilobite Collector’s Guide

Other recommended books mentioned in this review:

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If volcanoes make you giddy, then this is the book for you. Robin George Andrews is that rare hybrid of the scientist–journalist: a volcanologist who decided to focus on science communication after completing his PhD. Super Volcanoes combines scientific exactitude with engaging writing and is a tour of some exceptional volcanoes on Earth and elsewhere in the Solar System. Andrews starts it with an unabashedly enthusiastic mission statement: “I want you to feel unbridled glee as these stories sink in and an indelible grin flashes across your face as you think: holy crap, that’s crazy!” (p. xxi). For me, he nailed it and I found this an incredibly satisfying read.

Super Volcanoes: What They Reveal about Earth and the Worlds Beyond, written by Robin George Andrews, published by W.W. Norton & Company in November 2021 (hardback, 312 pages)

Super Volcanoes breaks down into two parts. The first four chapters cover volcanoes on Earth, including Hawaii, Yellowstone National Park, the Ol Doinyo Lengai volcano in Tanzania, and underwater volcanoes and hydrothermal vents. The last four chapters go off-world to our Moon, Mars, Venus, and moons such as Io and Enceladus.

In several chapters, Andrews delves into the history of his discipline. He introduces Harvard geologist Thomas Jaggar (1871–1953) who dedicated his research to better understanding volcanoes after investigating the aftermath of the destructive 1902 Mount Pelée eruption. He founded the Hawaiian Volcano Observatory that to this day does important work and features prominently in Andrews’s lively reporting on the 2018 Kilauea eruption. And then there is Marie Tharp (1920–2006) who identified the mid-Atlantic ridge when collating oceanic depth readings obtained by the US Navy. Initially, she was belittled by her supervisor for “girl talk” that might support the then-still controversial idea of continental drift. However, when another student mapped seaquakes that overlapped perfectly with her proposed ridge, he had to concede that she was correct. Her map would grace the cover of National Geographic and she was awarded the Hubbard Medal in 1978, which can be considered the Nobel Prize of the earth sciences.

But next to historic figures, Andrews has also tapped into his network of colleagues and here features lively conversation drawn from his many interviews. The enthusiasm he shares with his fellow scientists is infectious, no matter whether he discusses the geologic riches of Yellowstone with the resident scientist Mike Poland, Kate Laxton’s mission impossible to retrieve samples of the unique, runny carbonatite lava from Ol Doinyo Lengai, or Linda Morabito’s investigation of photos taken by the Voyager probes that revealed ongoing volcanism on Jupiter’s moon Io. Next to giving a good idea of what these scientists do and how they got interested in their fields of study, he also touches on the many questions that remain regarding volcanoes on Earth, but especially in our Solar System.

“though we often imagine a magma chamber as “a hollow lithological cathedral“, the actual plumbing of volcanoes is far more complex”

Two things, in particular, stood out for me. One is that Andrews is interested in correcting misconceptions. This might be a popular science book, but as a volcanologist, he knows his subject. He abhors how it often gets misrepresented by the “unrelentingly enthusiastic screaming of tabloid newspapers and social media crystal-ball mystics“. No, Yellowstone’s volcano is not “Earth’s self-destruct button” (p. 35) and the widely-adopted phrase supervolcano^[1] has a very specific meaning amongst volcanologists. And though we often imagine a magma chamber as “a hollow lithological cathedral“, the actual plumbing of volcanoes is far more complex. Better to imagine it as “a strange sponge, with the holes filled with a hellish gelatin” (p. 41).

The other stand-out of this book is the writing. In places, Andrews is concise, such as when describing the use of LiDAR to map lava flows obscured by vegetation as a technology “capable of virtual deforestation” (p. 15). Or how the study of extraterrestrial volcanoes “underscores a vital truth: that Earth may be normal to us, but the universe has other ideas” (p. 261). In other places, he is poetic, such as when depicting how microbial life survives , “dreaming in darkness within vaults of glass” (p. 137). Or how the tidal tug of gravity keeps the insides of extraterrestrial moons warm, long after primordial heat has dissipated and radioactive decay has slowed down. This allows for ocean worlds and cryovolcanism such as on Saturn’s moon Enceladus. “When it comes to keeping worlds alive, perhaps the tides of gravity are the only engines that transcend the tides of time” (p. 271). Foremost is his humour. Admittedly, pop-culture references to Star Wars and Game of Thrones might not amuse everyone, but I chortled when he described Venus “to be as habitable as the business end of a flamethrower” (p. 225). Or when he compares the two models of volcanism that might have created the enormous Tharsis rise on Mars; either as stack upon stack of erupted lava, “like hell’s idea of pancakes” (p. 184), or by the crust expanding as it is fed magma as if it were “a giant, Lovecraftian éclair” (p. 185).

” the study of extraterrestrial volcanoes “underscores a vital truth: that Earth may be normal to us, but the universe has other ideas“”

To conclude this review I have to make a quick comparison with Natalie Starkey’s Fire & Ice, which was published only a few months before Super Volcanoes. Both books cover very similar topics, including the same volcanoes, though Andrews includes much more detail on e.g. Ol Doinyo Lengai which Starkey mentions just once, or on the Martian Tharsis rise and the nearby Valles Marineris while Starkey focuses on Olympus Mons. Where Andrews has picked a select number of extraterrestrial locations, Starkey ranges wider in her Solar System tour. Super Volcanoes has a black-and-white illustration opening each chapter but could have used more—Fire & Ice at least had a colour plate section. It seems that the somewhat dated Alien Volcanoes is still the go-to book when it comes to pictures. In my opinion, Starkey puts the focus on education first with the entertainment factor a close second. She includes much about volcanism itself while telling the story in her own voice. Andrews puts entertainment first with the education factor a close second. He tells part of his story through the many scientists he interviewed. In my review of Fire & Ice, I mentioned the writing did not quite gel for me and this is where Super Volcanoes hit the sweet spot for me.

Overall, Super Volcanoes is a hugely entertaining book on a fascinating subject that met its goal of leaving this reader with a grin on his face. This is a great example of deeply informed popular science written by a knowledgeable author.

1. ↑ I like to think that the insertion of a space between “super” and “volcanoes” in the title is a deliberate in-joke on Andrews’s part—this is not a book about supervolcanoes, but about how super volcanoes are.

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

Super Volcanoes

Other recommended books mentioned in this review:

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Deep time is, to me, one of the most awe-inspiring concepts to come out of the earth sciences. Getting to grips with the incomprehensibly vast stretches of time over which geological processes play out is not easy. We are, in the words of geologist Marcia Bjornerud, naturally chronophobic. In Notes from Deep Time, author Helen Gordon presents a diverse and fascinating collection of essay-length chapters that give 16 different answers to the question: “What do we talk about when we talk about deep time?” This is one of those books whose title is very appropriate.

Notes from Deep Time: A Journey Through Our Past and Future Worlds, written by Helen Gordon, published by Profile Books in February 2021 (hardback, 322 pages)

For Gordon, a chance encounter with an outdoor information board during a walk on the North Downs near London ignites her interest in deep time. Before long, she is visiting museums and interviewing earth scientists and palaeontologists. Notes from Deep Time is thus very relatable to a general audience who, like Gordon, are not geologists. A few of the 16 chapters in this book have previously been published, but most are new. She has organised them around three topics: geology, extinct life, and the intersection of deep time with human affairs. Having introduced the concept of deep time and how the age of the Earth was slowly uncovered, she delves into palaeoclimatology, stratigraphy, plate tectonics, earthquakes, volcanic eruptions, dinosaurs, the Anthropocene, palaeoart, urban geology, nuclear waste, etc.

One enjoyable aspect is that Gordon brings in new perspectives, even for topics I was familiar with. When discussing ice cores, she explains the work of pioneer Willi Dansgaard and his discovery of rapid climatic changes subsequently named Dansgaard–Oeschger events. Initially eyed suspiciously by scientists, the idea was soon enough corroborated by evidence from pollen records and ocean sediments. Her discussion of dinosaurs is equally novel, and appropriately titled “what we talk about when we talk about dinosaurs”. She asks why children are so fascinated by them, how fossil dig sites have changed over time, how the palaeontological community is torn over the trade in fossils, and how the story of their extinction forms “an irresistible backdrop onto which to project our own fears of climate change and contemporary apocalypse” (p. 196), something explored further in Sepkoski’s Catastrophic Thinking. When visiting a dinosaur trackway in Utah, she reminds the reader that it is easy to lose sight of the beasts themselves. “Bombarded with plastic figurines and dinosaur memes, familiarity stops me really seeing a dinosaur. […] Touching the edges of one of the theropod’s lozenge-shaped toes, 150 million years almost dissolve in the hot desert air. There really were dinosaurs here. For a moment that fact becomes amazing once again” (pp. 198–199).

“In 2018, a terrible ruckus broke out when some stratigraphers proposed subdividing our current epoch, the Holocene, into three new ages, the most recent one being called the Meghalayan.”

I furthermore appreciated how Gordon pays attention to the subtleties and technicalities of topics. In two chapters she takes a surprisingly deep yet accessible dive into stratigraphy. In 2018, a terrible ruckus broke out when some stratigraphers proposed subdividing our current epoch, the Holocene, into three new ages, the most recent one being called the Meghalayan. Partially this was because others are still working on the stratigraphical case for the Anthropocene. She listens to the arguments put forth by both proponents and opponents of these concepts. She goes into a similar level of nuanced detail when discussing colour as deduced from exceptionally well-preserved fossils. The focus has so far been on melanosomes and the pigment melanin, but Gordon also interviews Maria McNamara who is looking at carotenoid pigmentation and structural colours. These discoveries allow palaeoartists to make more true-to-life reconstructions. An open-hearted conversation with palaeoartist Robert Nicholls touches on his Psittacosaurus model, the importance of thorough background research, and his frank opinion that most dinosaur art that gets published is “regurgitated nonsense” (p. 214). And while I had read about the plans for long-term underground storage of nuclear waste in Finland in Macfarlane’s Underland, Gordon adds an interesting discussion on the challenges of designing warning signs for distant future generations to stay away from such repositories.

Some chapters touched on, for me, completely novel subjects. There is a chapter on chalk, one of the least appreciated rock types amongst geologists. Here, she accompanies a team making a new map of the chalk formations underlying parts of Britain. She discusses the primitive fossil trees found in Gilboa in the USA, and their unusual mode of growth. Another chapter focuses on the difficulty of predicting earthquakes and volcanic eruptions, and highlights that part of the problem is the loss of hard-won knowledge and experience when scientists retire. And she opened my eyes to the phenomenon of urban geology, the idea that the materials used in buildings, especially older ones, can reveal more about local geology.

“When explaining how the theory of plate tectonics came together [Gordon] cleverly points out that “you can tell the story of plate tectonics in many different ways“, depending on whose contributions you focus on.”

What makes this wide-ranging collection of deep-time musings so captivating is Gordon’s language and sharp observations. She talks to the Geological Society’s librarian who highlights commonalities between poetry and geology: both involve “building worlds in your mind and presenting them to others using descriptive language” (p. 8). When we discuss history, we merrily skip over thousands and millions of years. As Gordon puts it beautifully: “if the human brain naturally compresses the past, then the scientists working with deep time are in the business of decompression” (p. 22). When explaining how the theory of plate tectonics came together, she of course pays homage to Alfred Wegener but cleverly points out that “you can tell the story of plate tectonics in many different ways” (p. 75), depending on whose contributions you focus on. And why, of all the proposed new stratigraphical units, has the Anthropocene taken such hold of the popular imagination? Gordon’s answer is that science has been in the business of knocking humans off their pedestal for several centuries. “Considered one way, then, the Anthropocene concept puts humans back at the centre of the world […] and at some level we can’t help finding that attractive—even if the price for that return is environmental disaster” (p. 244). The only thing I felt was missing from this book were illustrations and photos; many of the places and phenomena described here would have benefited from some.

Notes from Deep Time is a fantastic dive into the deep past of our planet that engages with deep time on many levels. Readers will find at least some, if not many chapters that will thoroughly captivate them and induce that most rare of sensations: “temporal vertigo” (p. 1).

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

Notes from Deep Time

Other recommended books mentioned in this review:

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What could be more awe-inspiring than volcanoes? How about volcanoes in space? Having previously raved about asteroids, geologist and cosmochemist Natalie Starkey returns to Bloomsbury Sigma for her second book. Here, she takes readers not just on a Solar System tour of volcanoes, but also walks them through the processes that make a volcano and how these processes play out in extraterrestrial settings.

Fire & Ice: The Volcanoes of the Solar System, written by Natalie Starkey, published by Bloomsbury Sigma (a Bloomsbury Publishing imprint) in September 2021 (hardback, 320 pages)

Fire & Ice is really a book in three parts. The subtitle leads you to believe this book is a tour of Solar System volcanoes, and it delivers this in the last three chapters. But it is as much about volcanism—about the process—as it is about volcanoes, with four chapters dealing with the nuts and bolts of how volcanoes work, and another three on the effects volcanoes have.

At its most basic, volcanism is a way for planetary bodies to cool down. Two chapters in the middle of this book tell you how this heat is generated (some of it is primordial, some of it is generated during a body’s lifetime) and how it is lost through conduction (always) and convection (only if the thermal gradient is large enough). Another chapter deals with magma, discussing some examples of relatively liquid (basaltic) and stickier (silica-rich) magmas. One important misconception Starkey corrects is that the magma chamber is a simple subterranean liquid pool. Rather, magmatic plumbing systems are a complex series of lens-shaped bodies interconnected by pipes that have tendrils and dead ends. A fourth chapter answers how we can know what is inside of a planetary body using direct and indirect evidence. Examples of the latter are a magnetic field or a fresh-looking surface with suspiciously few craters, both strong hints that a planet or moon has an active interior.

Next to these nuts-and-bolts chapters, three further chapters discuss all the things volcanoes have done for us. A number of famous historical eruptions illustrate the many destructive effects. Plate tectonics illustrates the flipside: volcanoes create new land and conditions favourable to life by releasing carbon dioxide and water into the atmosphere. But to make oceans you need just the right conditions. Venus, for example, probably had water once, though it is now a lifeless world characterised by a runaway greenhouse effect. One possibility Starkey sketches here is that Venus’s surface remained too hot for too long for oceans to form through condensation, water instead being lost to space.

“[…] our knowledge of volcanoes is, obviously, skewed towards Earth. […] However, Earth is not typical for volcanism in the Solar System.”

One of the more interesting things that Starkey highlights is that our knowledge of volcanoes is, obviously, skewed towards Earth. And it still holds many surprises, most volcanoes are submarine and have barely been explored. However, Earth is not typical for volcanism in the Solar System. Ice-spewing volcanoes (cryovolcanism) and nitrogen glaciers might sound otherwordly, but “perhaps Earth is the weird one” (p. 27). Most volcanoes on Earth occur where tectonic plates meet or separate. Hot-spot volcanism, which sees mantle plumes from deep within the planet rise to the surface to form volcanoes, is rarer on Earth, but the predominant mode of volcanism on other Solar System bodies. Hawaii’s shield volcanoes are thus a more representative model for most extraterrestrial volcanoes. One further difference is that on Earth the combination of hotspot volcanism with a moving overlying tectonic plate has created the chain of islands making up Hawaii. Mars’s gigantic Olympus Mons shows what can happen on a stagnant-lid world without plate tectonics: a single, 624-km diameter, 21.9-km high^[1] shield volcano.

This leads into the final part of Fire & Ice, the Solar System tour of volcanoes that probably sold you on this book. In three chapters, Starkey compares our Moon with Jupiter’s moon Io; discusses the evidence of past volcanism on our rocky neighbours Mercury, Venus, and Mars; and looks at cryovolcanism on moons. This is where the book delivers the goods and features some of the most interesting material. For example, Io is the only other place in the Solar System with “hot” volcanism. Venus has a uniformly “young” crust of 300–600 million years old and in lieu of plate tectonics may have seen a planet-wide overturning of its crust in the past when it had become too hot under its stagnant lid. On Mars, we have found a similar pattern of geomagnetic stripes that on Earth was one line of evidence for plate tectonics, though whether this supports past plate tectonics on Mars remains an open question. And then there are the moons.

Alien Oceans introduced me to the concept of other habitable zones with conditions favourable for life outside of the classic one that is determined by distance to the parent star. On these moons, heat is generated through friction when their insides are squeezed and stretched in response to tidal tugs from the parent planet or other moons. As revealed by various missions over the years, this results in ice-covered moons with liquid subsurface oceans. Here, geysers release plumes of water, salts, and hydrocarbons, while cryovolcanoes erupt magma consisting of e.g. cold slurries of ammonia–water and liquid methane. Starkey discusses Triton (Neptune), Enceladus and Titan (Saturn), and Europa (Jupiter). A surprise entry is Pluto, with a fly-by of the New Horizons mission revealing a fresh surface, though its heat source remains mysterious.

“[Tidal flexing] results in ice-covered moons with liquid subsurface oceans. Here, geysers release plumes of water, salts, and hydrocarbons, while cryovolcanoes erupt magma consisting of cold slurries of ammonia–water and liquid methane.”

Fire & Ice is fascinating, but there is something about the writing that did not quite gel for me. I found it hard to put my finger on it exactly, but the book feels a bit lacking in structure, ricocheting between various, sometimes technical topics without a clear central message. One small error that escaped proofing is the consistent use of superscripts rather than subscripts for chemical formulae. Another question is how Fire & Ice compares to the 2008 Alien Volcanoes, of which I recently bought a copy. To my knowledge, it is the only other popular book on the subject^[2]. It spends only two chapters on past eruptions and the process of volcanism, quickly focusing on the Solar System tour. It is illustrated throughout with photos from NASA and artwork from Michael W. Carroll, versus an 8-page plate section in Fire & Ice. Starkey’s work is, of course, fully up-to-date, covering missions and planetary bodies not mentioned in Alien Volcanoes, but I also noticed topics not covered by Fire & Ice. My quick impression is that these books can comfortably exist side-by-side and Alien Volcanoes remains worth seeking out if you do not already have a copy.

Despite some minor quibbles, Fire & Ice is a fascinating book for astronomy and volcano aficionados that is both a Solar System tour of volcanoes and a primer on how the process of volcanism plays out on Earth and beyond.

1. ↑ Confusingly, Starkey gives its height as 25 km on p. 38. Wikipedia also gives two figures, depending on whether you use height above geodetic datum (a reference frame) or local relief above the plains.

2. ↑ Since then W.W. Norton published Super Volcanoes, which also covers a few extraterrestrial locations.

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

Fire & Ice

Other recommended books mentioned in this review:

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Deep time is one of the most mind-boggling yet underappreciated concepts to come out of the disciplines of evolutionary biology and the earth sciences. As an editor with Nature for over three decades, Henry Gee has had a front-row seat to numerous exciting scientific developments that have enriched our understanding of Earth’s vast 4.6-billion-year history. This high-octane popular science book is his take on the genre of the “earth biography”.

A (Very) Short History of Life On Earth: 4.6 Billion Years in 12 Chapters, written by Henry Gee, published in Europe by Picador in September 2021 (hardback, 336 pages)

I admit that my initial response to this book was one of mild surprise: “wait, another one?” A (Very) Short History of Life On Earth was published in the same month as Riley Black’s Deep Time and only months after geologist Andrew Knoll’s A Brief History of Earth that promises to do the whole exercise in eight chapters. Further back, other notable examples have been Robert Hazen’s The Story of Earth and the now-classic Life: An Unauthorised Biography by Richard Fortey. Writing Earth’s biography almost seems like a rite of passage for science writers.

If you have read any of these books, or are familiar with the major events in life’s evolution, you already know what to expect. Earth’s formation, the start of plate tectonics, the rapid evolution of life, the Great Oxygenation Event, the first bacterial cells, endosymbiosis, multicellular life, the spinal cord, tetrapods making landfall, reptiles, dinosaurs, mammals, monkeys, and mankind—the whole circus comes rolling through town in high tempo.

“Gee focuses on those geologic periods and fauna that normally get little love in popular science books […] he sticks up for the fauna of Triassic that often gets overlooked in favour of the dinosaurs”

And yet, the history of life is so full and rich that every iteration of this story can draw on new details. An important backbone to Gee’s version is plate tectonics and the supercontinent cycle. As he explains, the breakup of Rodinia (Pangaea’s predecessor) was accompanied by so much volcanism and extrusion of fresh rocks that the subsequent erosion drew enough carbon dioxide out of the atmosphere to cause planetary-scale glaciation, the Snowball Earth episodes some time before 650 million years ago. In turn, the formation of Pangaea caused the climate on land to be far hotter, drier, and more seasonal. More recently, the opening of the Drake Passage allowed the Southern Ocean to flow uninterruptedly around Antarctica, shaping Earth’s climate to this day.

What I particularly enjoyed is that Gee focuses on those geologic periods and fauna that normally get little love in popular science books. There was the invertebrate fauna of the Ediacaran that defies categorization and makes even the weirdos of the Cambrian explosion look normal in comparison. Gee is similarly knowledgeable about the rise of the backbone and introduces you to vetulicolians and yunnanozoans, one of which, Cathaymyrus, “looked like an anchovy fillet […] sans head, sans scales, sans ears, sans nose, sans brain—sans nearly everything” (p. 38). He discusses the fantastic flora of the Carboniferous, and the unique conditions that gave rise to 90% of today’s coal reserves. And he sticks up for the fauna of the Triassic that often gets overlooked in favour of the dinosaurs. In reality, “the dinosaurs were a relatively small sideshow in the Triassic carnival of dicynodonts, rhynchosaurs, rauisuchians, aetosaurs, phytosaurs and giant amphibians” (p. 99).

Indeed, when he gets to the dinosaurs, Gee cleverly refrains from trying to write an overview, as so many excellent books already exist on this topic. Instead, he focuses on several biological aspects that made them so successful: the evolution of bipedalism, the innovations in respiration that allowed them to grow so large, and the transition to powered flight. This is embedded in the history of mammal evolution that simultaneously happened in the background, though I was surprised to find no mention of Panciroli’s Beasts Before Us, which is the current go-to book on this topic.

“Gee repeatedly reminds his readers that evolution is not goal-directed. […] one group of ungulates “with enthusiasm, and, in evolutionary terms, great haste” returned to the water and evolved into whales.”

Some other enjoyable details include an increasingly zoomed-in timeline^[1] at the beginning of some chapters—too few books use good infographics. Gee’s extensive footnotes are frequently as interesting as the main text, provide plenty of further references, and clearly signpost where he ventures into speculation. Some of his writing is particularly memorable. Of the first cells, he writes that: “these foamy lathers of soap-bubble cells stood as tiny clenched fists, defiant against the lifeless world” (p. 7), while the evolution of photosynthesis that harnessed previously damaging UV radiation meant that “harm had become harvest” (p. 8).

Importantly, Gee repeatedly reminds his readers that evolution is not goal-directed. “It wasn’t as if eukaryotes looked at their calendars, and, seeing that it was 825 million years ago, unanimously decided to become multicellular” (p. 217). Furthermore, “the tetrapod commitment to land was, for many millions of years, no more than equivocal” (p. 68). Both early and modern birds have secondarily lost flight on numerous occasions, while one group of ungulates “with enthusiasm, and, in evolutionary terms, great haste” (p. 141) returned to the water and evolved into whales. And the profusion of early hominins should not “give the impression that a series ever more bipedal species replaced one another in some orderly, preordained fashion” (p. 155). There is one place where Gee seemingly throws this caution to the wind: “Dinosaurs had always been built to fly” (p. 105) and “[…] spent millions of years accumulating everything they needed for flight” (p. 113). In hindsight, it seems the writing was on the wall, but I was reminded of Neil Shubin’s insight that: “innovations never come about during the great transitions they are associated with“.

“Gee looks ahead with an unusual mix of optimism and nihilism […] Ours is but a “mayfly existence“. This reminder of our cosmic insignificance is a sobering but fitting conclusion to [his] epic tale.”

The first two-thirds of A (Very) Short History of Life On Earth are, in my view, the strongest. After the end of the Cretaceous, the book takes a rather anthropocentric bend, focusing on primate and hominin evolution only, as if life was on the highway to humankind. What, for example, of the explosive radiation of birds? Gee also stops rather abruptly with our departure from Africa and our interbreeding with Neanderthals and Denisovans. Recent milestones, such as language, animal and plant domestication, and agriculture are skipped over.

Instead, in his last chapter, Gee looks ahead with an unusual mix of optimism and nihilism. In an upbeat manner, he writes that we are already phasing out fossil fuels and can expect our world population to plateau. Part of his optimism might stem from his agreement with e.g. Michael Hannah that technically it is too early to be speaking of the sixth mass extinction. On the other hand, he thinks our extinction is merely a matter of thousands of years. When he reflects on the long-term future of Earth, he asks: “What, then, will be the human legacy? When measured against the span of life on Earth—nothing. The whole of human history, so intense and so brief […] will leave no more than a layer, millimetres thick, in some future sedimentary rock“. Ours is but a “mayfly existence” (pp. 232–233). This reminder of our cosmic insignificance is a sobering but fitting conclusion to Gee’s epic tale.

In 1997, Ted Nield wrote of Fortey’s book that “The tale of life needs constant retelling“. I believe this sentiment still holds, both because our understanding advances and because we need periodic reminders of the importance of deep time. Gee succeeds on both these fronts and dishes out interesting nuggets at a brisk clip, making A (Very) Short History of Life On Earth a high-octane popular science book.

1. ↑ This reminded me of the introduction to the sitcom The Big Bang Theory, and there is more than a passing resemblance between the theme song by Barenaked Ladies and Gee’s energetic take on the subject.

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

A (Very) Short History of Life On Earth

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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Life most likely originated in the oceans, and it is to oceans that astronomers are looking to find life elsewhere in the universe. With the publication last year of Kevin Peter Hand’s Alien Oceans, I decided this was the right time to finally review Ocean Worlds, a book that I have been very keen to read ever since buying it some years ago. This, then, is the first of a two-part dive into the story of oceans on Earth and elsewhere.

Ocean Worlds: The Story of Seas on Earth and other Planets, written by Jan Zalasiewicz and Mark Williams, published by Oxford Press in December 2017 (paperback, 302 pages)

Palaeobiologists Jan Zalasiewicz and Mark Williams have previously collaborated on The Goldilocks Planet. Here, they provide a deep history of our oceans. As soon as I tucked in, it became clear that they go deeper than Eelco Rohling did in the previously reviewed The Oceans: A Deep History, a book that focused heavily on palaeoclimatology. Even though most of the action in Ocean Worlds takes place on Earth, and the wider universe is only considered in the opening and closing two chapters, the book is characterised by an almost cosmic perspective on the subject. The writing of Zalasiewicz and Williams is such that I felt as if was surveying major developments in the history of our universe from an elevated, slightly detached, almost omniscient position. The result is thrilling and at times awe-inspiring. What follows are some of the big questions and outrageously fascinating topics they consider.

To have an ocean we first need water. Hydrogen was an immediate byproduct of the Big Bang. Oxygen, however, did not appear until after the universe had gone through its first cycle of stars being born and dying, as its creation required nuclear fusion. Likely, the formation of water had to wait for a few hundred million years, though some have argued it could have started much sooner. As is usual when dealing with processes that took place in such a distant past, opinions are divided and there are several reasonable scenarios.

“the book is characterised by an almost cosmic perspective on the subject […] The result is thrilling and at times awe-inspiring.”

With water present in the universe, how did Earth acquire its oceans? After all, “There is a wild card here, which surely had an impact” (p. 18). We have good evidence that our proto-Earth, called Tellus by some, was hit by a small planetoid, Theia, with the resulting debris forming our current Earth–Moon system. This event would likely have obliterated what early oceans we had, if any. Various authors have proposed that certain meteorites (carbonaceous chondrites) or comets might have subsequently been water’s cosmic delivery vehicle.

However it got here, the first major effect it had was kick-starting plate tectonics. The early Earth was hot, but without the lubrication provided by water, the heat-venting mechanism of plate tectonics was not in place. How did molten rock make its way to the surface? Some scientists argue that it was through simple vertical conduits, so-called heat pipes, which would have made for a radically different surface topography: “the fundamental proportions of land area and ocean area […] would have been utterly different to today’s familiar patterns” (p. 34). Though, again, this idea is contested by others. The puzzle of when plate tectonics started, possibly 3 billion years ago, relies on truly ancient rocks, 3.5 to 3.8 billion years old, of which we have precious few remaining in places such as Australia and Greenland.

Beyond those earliest days, Ocean Worlds has much interesting material about later episodes. Life likely started in the oceans, this much I knew, but these were iron seas. Water without oxygen can hold large amounts of dissolved iron, and early organisms used this in their biochemistry to generate energy. This was the realm of the Archaea: the salt-tolerant, heat-loving, chemoautotrophic microbes for whom oxygen was poison and the Great Oxygenation Event murder. It was also a time when banded iron formations (BIFs) were built up, relevant to us today as they formed the ore deposits providing most of our iron and steel. Though, as clarified here, their formation was anything but straightforward. Other fascinating episodes are the Messinian Salinity Crisis, some 5.6 million years ago, when the Mediterranean repeatedly dried up, leaving behind kilometre-thick salt layers that reduced global ocean salinity.

“However it got here, the first major effect [water] had was kick-starting plate tectonics.”

Of course, a book about oceans has to consider current human impacts. With due diligence, the authors tackle the problems of overfishing, shifting baselines, trawling, litter, ocean warming, oxygen loss, and acidification, and conclude that: “there currently seems not the faintest chance of stopping carbon emissions over many decades, let alone overnight” (p. 191). Does this sound gloomy? I prefer the word “sobering”. Consider, they write, that the “more-than-tripling of human population” (p. 183) was enabled by the invention of the Haber–Bosch process and the plentiful artificial fertiliser it made available. To this, they add geologist Peter Haff’s argument of the technosphere that resonated with me. “The 7 billion humans on Earth today are kept alive only through the continuous action of an enormous, globally interlinked system of transport and communication, metabolized by the use of vast amounts of energy […] Without it, most of us would not be alive—and therefore we are forced to keep it going” (p. 197).

If that was not sobering enough, what really made me feel small was when they pulled back from our timescale and the current “brief ecological wrecking spree” (p. 195), to the long-term future. Our oceans are not forever. As the Sun grows hotter they will evaporate, though the “end of the oceans is not likely to be simple” (p. 207). Whether through a moist greenhouse phase where water is gently siphoned off into space by solar winds, or a runaway greenhouse hot enough to melt rock, a dry future awaits, and plate tectonics will once again grind to a halt. As this process “is unlikely to simply just stop, smoothly and without fuss” (p. 211), expect some extraordinary landscapes.

“Our oceans are not forever. […] Whether through a moist greenhouse phase where water is gently siphoned off into space by solar winds, or a runaway greenhouse hot enough to melt rock, a dry future awaits.”

Amidst these grand, cosmic scenes, the authors highlight the human stories behind this research. Such as the pioneering contributions to oceanography by the people on board the HMS Challenger expedition, the mapping of the seafloor by Marie Tharp, or the work of Wally Broecker who established a link between ocean currents and rapid climatic changes. And while Svante Arrhenius is better remembered for linking historical changes in carbon dioxide concentrations to past ice ages, both he and Fritz Haber tried to extract gold from sea water. Unsuccessfully, I might add.

In the last two chapters, the authors turn their gaze to the skies once more, discussing past and present oceans inside and outside of our solar system. With the many discovered by the Kepler space telescope, “We are on the verge of not just a new chapter in oceanography—or exo-oceanography, if you like—but of setting up an entirely new library of oceans, for the diversity and complexity of cosmic oceans will be beyond anything that we can dream of” (p. 264).

I explore this topic more in-depth in my review of Alien Oceans. But, as a warming-up exercise and a proper deep history of oceans, Ocean Worlds is a fantastic book that strikes the right balance. Zalasiewicz and Williams present fascinating science with enviable ease, without smoothing over the fact that science is rarely a straightforward affair, proceeding by means of conflicting scenarios and competing hypotheses. The deep-time perspective and big questions asked make this one awe-inspiring book.

Ocean Worlds

Other recommended books mentioned in this review:

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