As the smoke spiralled lazily around us, Xavier pointed out details and patterns in the charred vegetation, explaining what they revealed about the fire history of the landscape. We paused in front of a fallen eucalypt, its blackened trunk glistening with grids of charcoal. Under a microscope, these cube-like chunks can be read for information about the species of the tree, when it was seeded, and the intensity of the fire that consumed it. In an ancient campsite, charcoal residue gives us an insight into the role of fire in past societies: how people have harnessed flame over millennia.

Geologist and palaeobotanist Andrew C. Scott shares this fascination with charcoal – indeed, he is one of the world’s leading charcoal specialists – but he approaches fire from a very different timescale. His new book, Burning Planet: The story of fire through time, begins with the evolution of the first vascular land plants – or fuel – during the Silurian Period, some 420 million years ago. He charts the explosion of plant biodiversity in the Carboniferous Period, 359–299 million years ago, when fire was ever-present and the trees mainly responsible for today’s coal evolved. Some one hundred and forty million years ago, flowering plants appeared, adding vibrant colour to the Earth of the Lower Cretaceous, and, from thirty million years ago, grasses evolved and diversified.

Deer taking refuge in a fire in Bitterroot Valley of Montana (photograph by John McColgan)

In his sweep of deep time, Scott looks at the role of fire in the past five mass-extinction events, but he doesn’t touch on the idea of a human-induced ‘sixth extinction’. He acknowledges the grim realities of anthropogenic global warming, but his main focus is on the world before people. He wants to understand the ‘fundamental elements of fuel, heat, and oxygen on geological timescales’. Humans don’t enter his story until the last thirty pages of the book.

Scott’s relationship with fire began in the early 1970s, when, as a graduate student, he embarked on a series of experiments comparing fusain (a fossil material) with modern charcoal. He charred conifer leaves in his mother’s oven, made charcoal in a garden bonfire, and then compared these samples with fusain under a microscope. His study of their cell structures revealed that they were essentially the same material: fusain was fossil charcoal. It was a major breakthrough in palaeobotany and unexpectedly propelled Scott into a career devoted to fire. With Burning Planet, he seeks to synthesise his life’s work.

The book is global in scope and directed towards a lay audience. Scott writes clearly and with great enthusiasm for his subject matter, although the narrative occasionally reads like a textbook – ‘Charcoal 101’. It is richly illustrated, with evocative reconstructions of past landscapes, vivid photos of bush fires, and striking ‘micrographs’ of charcoalified plants.

The 2015 North Fire in southern California

The binding thread of Burning Planet is the anecdotal account of Scott’s research career, which has unfolded at a time of great change in his discipline. The catalyst for these advances, he explains, has been the development of real-time satellite imaging: ‘It is only when we see images … from space that we realize the scope and scale of wildfire on Earth.’ Even political boundaries, such as the Sino-Russian border (where two fire regimes meet), are decipherable from space. Satellites help track plumes of smoke from the peat fires of Indonesia as they merge and drift northwards towards Singapore and Malaysia. They also allow daily monitoring of the main source of ignition: lightning.

There are roughly eight million lightning strikes every day on Earth. Some of these strikes are preserved in the geological record, where the heat of the lightning has melted grains of sand into fossilised tubes. An event that lasted an instant has marked the Isle of Arran for the past 260 million years.

Scott’s journey into deep time serves to illustrate his central argument: that fire is a force of nature. The planet has been burning for hundreds of millions of years. All plants and animals evolved with fire, and many need it to spread, survive, and reproduce. It is impossible to remove fire from the landscape: ‘we have to learn to live with fire’.

Humans, of course, have also evolved with fire. Over the past two million years, the Homo genus has learnt to use fire for cooking, hunting, land management, and myriad social, cultural, and political purposes. Fire has changed our biology, and people have used fire to transform ecosystems and fire regimes. Scott acknowledges that the word ‘natural’ seems unsuitable when referring to ‘a habitat that has been managed by humans for hundreds or even thousands of years’. But sadly he does not explore Indigenous burning in any great depth. The cultural burns that Xavier and I observed in Arnhem Land lie outside his narrative, as does the humanist perspective that historian Stephen J. Pyne brings to his fire histories.

Scott finishes by reflecting on the future of fire in an increasingly globalised world, and especially the ecological consequences of invasive plants. The introduction of eucalypts to Portugal, for example, has altered the local fire system. Eucalypts, which have evolved to burn, fuel more severe and intense fires that have spread into native vegetation and urban areas with disastrous consequences. Scott warns that ‘with climate and vegetational changes, fire may become a problem where it was not in the recent historical past’. He even worries about fires in his home county of Surrey in the United Kingdom: a densely populated, forested area with regular controlled surface fires. ‘Imagine the havoc if any of these fires should become major crown fires,’ he exclaims. ‘Can we plan ahead?’

Scott touches on the toll of fire on communities – ‘amply illustrated by the Black Saturday wildfires of 2009 in Victoria’ – and laments that ‘there still appears to be little general understanding of wildfire’. But he hesitates to be too explicit in his prescriptions, instead weighing up the evidence with detached concern. On the question of prescribed burning in heathlands, for example, he writes that ‘this is a complex issue with no completely right or wrong answer’.

There is something refreshing, albeit academic, about this approach. Scott is, at heart, a scientist. He is diligent about his references, cautious in his interpretations, and explicit about his caveats. He is seeking to share with others his fascination with fire, as well as his fears for the future of this burning planet.