Fire is a force of nature that both fascinates and frightens. Large wildfires around the world seem to be on the rise and are a cause of concern due to the risk to lives and property. But fire also is an essential part of the workings of our planet that pre-dates humans by a long time. How long? For the last 40 years, geologist and palaeobotanist Andrew C. Scott has researched plant remains in the fossil record that have been preserved by fire in the form of fossil charcoal. In Burning Planet, he takes you on a 400-million-year deep-history tour of fire and how it has shaped our planet.
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 is 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 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.
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