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

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

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

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

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

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

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

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

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

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

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

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

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

Land Bridges paperback, hardback or ebook

Other recommended books mentioned in this review:

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“Earth History and Palaeogeography“, written by Trond H. Torsvik and L. Robin M. Cocks published by Cambridge University Press in December 2016 (hardback, 317 pages)

Trond H. Torsvik and L. Robin M. Cocks, both established geologists, draw on a huge body of interdisciplinary knowledge for this book. This includes, amongst others, palaeomagnetism and polar reversals (see my recent review of The Spinning Magnet: The Force That Created the Modern World – and Could Destroy It for an introduction), past volcanic eruptions, geophysics and tomography (a technique to visualise the inside of the planet), the rock record, and fossil distribution. Putting this all together allows them to reconstruct the face of the Earth over the last 540 million years. We know that plate tectonics was happening earlier in time as well, the geological story at the heart of the lyrical A Wilder Time: Notes from a Geologist at the Edge of the Greenland Ice was that we have evidence for plate tectonics as far back as approximately 2 billion years, and this book even mentions 3 billion years. But details just become too sketchy to make reliable planetary-scale reconstructions. So, as the authors make clear, this is by no means the definitive story but a work in progress. This book shows the current state of our knowledge, which will no doubt be further refined in the future.

After outlining their methodology and introducing, with maps, all 268 tectonic units that they have recognised as currently making up the surface of our planet (that’s a lot more you typically see on schematic maps) we get to the bulk of the book. This consists of eleven chapters that cover each geological period from the Cambrian (541-487 million years ago) to the Neogene and Quaternary (23 million years ago to today). Each chapter starts with several overview maps of the whole planet at various stages of each geological period which are already worth their weight in gold if this floats your boat. But that’s just the beginning.

“[these] overview maps […] are already worth their weight in gold if this floats your boat.”

A large number of maps and diagrams show different projections and perspectives, systematically going through each of the major continents as they existed back then. These maps show current continent outlines and estimated coastlines and deep and shallow seas back then, but also divisions between plates where the seabed was spreading apart or where plates were being subducted or colliding to form mountains chains. Symbols indicate approximate locations of major reefs, ice caps, lakes, areas of volcanic activity including large igneous provinces (the massive volcanic eruptions implicated in mass extinctions that we met in The Ends of the World: Volcanic Apocalypses, Lethal Oceans and Our Quest to Understand Earth’s Past Mass Extinctions), areas where coal was deposited, areas that dried up and left evaporites, faunal provinces that show the distribution of important fossil groups, as well as side-bars with approximate sea-level and climate conditions compared to today, and many other details. In the later chapters on geologically younger periods, when more details can be reliably reconstructed, many other diagrams and maps are shown, detailing the formation of mountain ranges such as the Himalayas, the appearance and disappearance of oceans, movements of the oceanic plates, etc. etc. The amount of information that is packed into these figures is breathtaking.

The text, meanwhile, links together the different events depicted and provides further context and details. Some things cannot be shown on the maps, such as the location of certain minor plates. We know they were somewhere, but we often lack enough information to place them on a map in any meaningful way. The text not only covers the geological details but also contains a section describing the dominant flora and fauna and important developments in the evolution of life during the period in question.

The book is not what you would call bedtime reading (though that did not stop me from doing so anyway) and is suffused with jargon. This comes from three sources. All geological periods are divided into shorter stages that have their own names, as shown on the official International Chronostratigraphic Chart that is printed on both endpapers. All 268 tectonic units have their own names that are introduced in detail in chapter 3. But on top of that is the terminology for geological processes and rock types. This is where my decision to study biology rather than geology comes back to bite me (I am looking at investing in some undergraduate geology textbooks because the subject continues to interest me). So if, like me, you can’t tell your ignimbrite from your gneiss, or don’t know the difference between volcanoclastic intercalations and diachronous migration, you might struggle with the text. Now, to fault the book for this would be completely missing the point. This is an advanced-level reference work, squarely aimed at an audience of geologists and palaeontologists with the relevant background knowledge – but it is good to know going in. Even so, with my limited knowledge of geological processes mostly gleaned from popular academic books, I was able to follow the grand narrative just fine. And what a fantastic story it tells!

“This […] advanced-level reference work [is] squarely aimed at an audience of geologists and palaeontologists with the relevant background knowledge”

I cannot think of another book that takes such a clear, graphic approach as Earth History and Palaeogeography does. Not being familiar with the field, I am hesitant to claim this is a first, but it is obviously a very valuable compilation of the current state of our knowledge. For geologists and palaeontologists this is a mandatory reference work, but academically-minded book readers might also find this very interesting. I expect I will regularly be pulling it off the shelf to consult it while reading other books on palaeontology or geology.

For those interested, there are supplementary online resources, including several programmes that allow you to make your own reconstructions, including graphics and maps like the ones shown in the book. I have not played around with this, but it is fantastic to see the authors willing to keep this project alive post-publication.

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

Earth History and Palaeogeography hardback or ebook

Other recommended books mentioned in this review:

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“Burning Planet: The Story of Fire Through Time”, written by Andrew C. Scott, published by Oxford University Press in March 2018 (hardback, 231 pages)

Scott kicks off with an introduction to how we measure wildfires on a global scale, how satellite imagery has transformed our understanding of the scale and frequency of it, what different types of wildfire exist, what their sometimes unexpected aftermath is, and how plants deal with – and in some cases have evolved to take advantage of – fire. But we are here for the charcoal. Scott describes how it is formed, and how geologists, not without lengthy debate, finally realised that certain mineral deposits are actually fossilised charcoal. The level of preservation of microscopic details that are revealed once you put this under the microscope is astounding. The black-and-white plate section contains some amazing images of fossilised leaves and flowers (flowers!), hundreds of millions of years old, that have been preserved in exquisite detail. To the point that you can count leave pores, and, based on their density and comparison to contemporary plants, reconstruct CO₂ levels in our deep past.

Wildfire requires fuel (usually vegetation), oxygen, and a spark. It was therefore only once land plants evolved from 420 million years ago onwards that wildfires started occurring. Over this long time span atmospheric oxygen levels also varied. Nowadays our atmosphere contains 21% oxygen, but that wasn’t always the case, and quite some pages are spent on the various attempts at reconstructing historical oxygen levels over time.

Scott then walks the reader through the evidence for fire in different geological periods, going from deep time to the present. This section gets technical at times as Scott goes into the minutiae here. But it is interesting to see how there were periods where fossil charcoal suggests fires were frequent, while during other periods very little fossil charcoal is recovered. Some of this seems to have been due to periods of low atmospheric oxygen levels, whereas at other times mass extinctions decimated vegetation to such an extent there was not much left to burn.

“[…] The level of preservation [in charcoal] is astounding […] fossilised leaves and flowers (flowers!)”

Scott puts to rest one hypothesis that keeps being refloated; the idea that the meteorite impact that finished off the dinosaurs (see Alvarez’s T. rex and the Crater of Doom) also led to a global conflagration. It sure sounds dramatic: a massive meteorite impact followed by an intense global inferno. But fossil charcoal does not support this idea, with charcoal being found before, during and after the impact layer, and there being no qualitative differences in the charcoal indicative of higher temperatures.

Of course, any book dealing with the history of fire will have to talk about fire in human evolution. Probably its most transformative impact was that it allowed us to cook food. In Catching Fire: How Cooking Made Us Human, Richard Wrangham argued that this allowed for the evolutionary development of larger brains. But Scott also walks us through some other archaeological evidence for the use of fire. As we get closer to the present, there are other proxies and sources we can use, such as fire scars visible when cutting down trees and looking at their tree rings. This has allowed the reconstruction of a finer-grained picture of the recent history of fire.

Scott ends with a discussion of fire management. Without going into too much detail or prescribing management strategies, he highlights how there are arguments for and against trying to manage and prevent wildfire. Especially in the US, there is plenty of evidence to suggest that decades of preventative measures have increased the amount of dead, flammable plant material in forests. Once wildfires do occur, as they ultimately must, they burn far more intensely and destructively. And then there is the question, as with the risk of flooding, whether we should really be building houses where we are building them. Let alone whether we should be putting the lives of firemen at risk when they are called out to such areas.

“[…] It sure sounds dramatic: a massive meteorite impact followed by an intense global inferno. But fossil charcoal does not support this idea […]”

Throughout, the book is illustrated with photos and graphs. I already mentioned the black-and-white plate section, but there is also a very nice colour plate section with some striking images. Some of the illustrations in the main body of the text are graphs that have been reproduced from papers and are fairly technical. They are typical of the kinds of deep-time / stratigraphy illustrations in this discipline. Although some annotations are provided, I can see readers not familiar with these puzzling over them for a bit.

Scott has previously contributed chapters on fire in deep history to textbooks such as Fire Phenomena and the Earth System: An Interdisciplinary Guide to Fire Science and more recently Fire on Earth: An Introduction. Burning Planet is, however, the first book-length treatment exclusively on this topic. Even if the narrative gets a bit technical in places, Scott’s dedication to the subject and the history he reconstructs here are amazing. If you have any interest in deep history and palaeontology this book is easy to recommend and will add an extra perspective on what you might already know.

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

Burning Planet hardback, ebook, audiobook or audio CD

Other recommended books mentioned in this review:

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“Squid Empire: The Rise and Fall of the Cephalopods”, written by Danna Staaf, published by ForeEdge, a University Press of New England imprint, in December 2017 (hardback, 237 pages)

Cephalopods have a long and illustrious evolutionary history, stretching back some 500 million years. The fact that they are still here means they have lived through their fair share of mass extinctions. After some basic morphology, Staaf quickly introduces us to the three groups on the family tree, as these are the main protagonists whose fate we will follow here.

A large chunk of the book deals with the now-extinct group of Ammonoids whose familiar whorled fossil remains are so numerous that they can be used to date rock strata. Although many species went extinct at the end of the Devonian, Permian and Triassic, some members of the lineage managed to survive, allowing the group to thrive, again and again, all the way until the end-Cretaceous. With Brannen’s recent The Ends of the World still fresh on my mind I was quite familiar with the details, but if you’re not, Staaf does an excellent job in giving a balanced picture of the various mass extinctions. She is equally capable of giving a short history of the Alvarez impact hypothesis, as she is able to explain anoxic events or large igneous provinces and flood basalts.

The second group are the slow-and-steady (evolutionarily speaking) Nautiloids who seem never to have diversified terribly much, but have kept on keeping on to this day. And, finally, there are the Coleoids who radiated to become today’s cuttlefish, squid and octopuses.

“[…] ongoing academic discussions are combined with Staaf’s narrative which is fiendishly readable”

And yes, I said octopuses rather than octopi. Staaf provides the best overview I have read so far of the whimsical discussion around how to pluralise this word. But far from mere whimsy, this book provides page upon page of fascinating insights. Whether it’s the intricacies of evolving buoyancy mechanisms allowing cephalopods to float, the way Coleoids internalised and in some groups virtually eliminated their shell, the continued confusion around the lower jaw or aptychus of the Ammonoids, or the arms race between cephalopods and their predators (first fish, then whales)… who knew there was so much fascinating research buried in the scientific literature?

Being a marine biologist herself, she is well-situated in these academic circles and has interviewed many scientists including Christian Klug, Dieter Korn, Kenneth de Baets, and Isabelle Kruta, all of whom are editors on the 2nd edition of the Ammonoid bible Ammonoid Paleobiology. Interesting findings and insider insights into ongoing academic discussions are combined with Staaf’s narrative which is fiendishly readable. In my opinion, her writing style strikes just the right balance between informative and understatedly entertaining (I sniggered throughout the book), without feeling forcedly funny. Admittedly, I have a soft spot for these squishy invertebrates, but I tore through this book in the space of a single seven-hour sitting! Squid Empire is a shining example of good use of illustrations supporting the text, especially the cephalopod family tree on page 46 is something you’ll be referring to time and again and has some clever details. Next to that, the book is also beautifully designed with stylised chapter headings and a beautiful Haeckel lithograph gracing the cover.

Dinosaurs may have time and again stolen the limelight, but Staaf shows an accessible book on the evolutionary history of cephalopods has been long overdue. With Squid Empire – which, can you believe it, is only her first book – she has established herself as cephalopod-champion par excellence. I know that 2018 has only just started, but already this book will be a strong contender as my book-of-the-year. This, ladies and gentlemen, is how you write a good popular academic book.

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

Squid Empire hardback, ebook or audiobook

Other recommended books mentioned in this review:

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