A review of ‘The Earth after us: what legacy will humans leave in the rocks?’ by Jan Zalasiewicz. Oxford, Oxford University Press. 2008.
The view of the Earth from the Moon on the front of the book seems both familiar and strange at the same time. The blue jewel of a planet is recognisably ‘home’, only a few decades since space travel first made such a perspective possible. But look again and an important difference is noticed. The continents are the wrong shape, and in the wrong configuration. Is this a view of our planet in the distant past? No, this is the Earth as it is imagined to be 100 million years into the future.
Geologist Jan Zalasiewicz invites the reader to take a step in the scientific imagination far greater than that involved in looking at the Earth from the Moon. For the challenge taken up by the book is to look back at human civilization from a vantage point in time long after the human species itself has disappeared, through observations made by alien beings visiting the planet for the first time. Seeking to understand the geological strata encountered, the alien scientists soon realise that something significant happened 100 million years ago, comparable to the meteorite strike that wiped out the dinosaurs even further back in the Earth’s past. Even before they discover it, they deduce the existence of an event horizon, separating two major geological epochs – an event that triggered massive climate change and extinctions of species evident in strata from later periods. Following a trail of clues, they discover the Human Event Stratum.
The Human Event Stratum may vary from a thin sliver to several metres in thickness, sandwiched between layers of sandstone and shale. Parts of it will have been destroyed by erosion or other geological processes. It is mostly buried, hundreds of metres under the ground, but in places it has been pushed up or exposed by geological forces to outbreak on the surface. Ever wondered what will survive, millions of years hence, of our railway networks, skyscrapers, motorways and rubbish dumps? What about trains and cars, or smaller artefacts like mobile phones and ballpoint pens? Such are the questions which the book poses. In this review I consider briefly some of the implications this book has for contemporary archaeology.
Much of the book is taken up with outlining the geological processes at work over timescales of millions of years, such as plate tectonics. Zalasiewicz gives an account of the immense pressures, stresses and temperatures which the Human Event Stratum will have to withstand if it is to have a chance of survival and possible future discovery. He discusses how the various materials of human artefacts and structures – metals, glass, concrete, plastic, and so on – may break down, endure, or be transformed through fossilization.
The key part of the book for archaeologists starts about three-quarters of the way through on page 165, with discussion of ‘urban traces’. Here the author considers the probabilities of survival of traces of urban centres. Alas for upward-moving cities like Manchester and San Francisco, the only remains are likely to be fine particles of sand or eroded lumps of mud and concrete washed down by rivers to the sea (tough luck on institutions like the Greater Manchester Archaeological Unit or the University of Stanford!). But low-lying and ultimately sinking cities, such as New Orleans, Amsterdam or Shanghai, stand a much better chance of being buried and preserved in the Human Event Stratum.
Dominating the Human Event Stratum in places, then, will be what the author calls the ‘Urban Stratum’. Representing the fossilised remnants of our great cities, this could be many metres in thickness even after compression by the accumulation of strata above. There will be no standing ruins. Upstanding buildings will long since have been toppled and crumpled, sometimes ground to rubble, and the rubble itself subjected to further erosion, burial , sedimentation, metamorphosis, and other geological processes. It is the underground foundations of buildings – piles, concrete rafts, basements and ‘made ground’ – that stand a better chance of survival. Of particular interest are the networks of pipes, subways and other subterranean tunnel systems that burrow beneath the urban landscape. Zalasiewicz points out that these ‘fossil burrows’, twisted and compressed, could be distinctive features of the Urban Stratum.
Examine the Urban Stratum at close hand, perhaps scrape away at it with a trowel-like implement, and this is what might be discerned:
“…compressed outlines of concrete buildings, some still cemented hard, some now decalcified and crumbly: of softened brick structures: of irregular patches of iron oxides and sulphides representing former iron artefacts, from automobiles to AK-47s: of darkened and opaque remnants of plastics: of white, devitrified fragments of glass jars and bottles…” (Zalasiewicz, p189).
Exactly what the alien discoverers of the Urban Stratum might make of this evidence is another matter. The difficulties of interpretation experienced by archaeologists today, looking back over periods of mere thousands of years at the material remains of our own species, will be compounded a thousand-fold in looking back 100 million years at the fossilized traces of what would be (to the hypothetical discoverers ) an alien civilization. Zalasiewicz suggests some of the inferences they might make about human life, and the sometimes surprising conclusions they might draw. There are fascinating insights about the character of archaeological interpretation in general, thrown into sharp relief by being placed in such a different temporal context.
The book makes us think differently about archaeology of contemporary architecture and material culture. It poses the questions – how might a subway like this be represented in the Human Event Stratum, 100 million years from now? How might it be interpreted? By whom?
Viewed from a standpoint 100 million years into the future, the mere 10,000 years of development of civilization, or the few million years of human evolution, might well be conflated into a single, possibly catastrophic, geological event. A major insight here is the extent to which, even if we were to become extinct tomorrow, the human species has made its mark on the planet. Technological and natural processes have already become so inextricably interlinked that “our actions now will literally be raising mountain belts higher, or lowering them, or setting off volcanoes (or stifling them), or triggering new biological diversity (or suppressing it) for many million years to come” (Zalasiewicz p240).
It follows from this that the form the Human Event Stratum (and indeed all subsequent strata) will take in the geological record is dependent to a large extent on actions taken now. The author gives us one possible version of how things will turn out – an apocalyptic vision of environmental collapse brought about in part by our own actions and inactions. But there are other possible outcomes. The imminent closure of the human event horizon is not inevitable, but still within our power to change. The book shocks us into a recognition of the urgency of the situation.
The Earth After Us has implications for all of us, but in this review for the Archaeolog website it is worth attempting to draw out some of the particular implications it has for archaeologists.
As archaeologists we are used to viewing the past from, as it were, within human event horizons. That gives us a very particular, situated perspective. To us the sequence of archaeological deposits ends with the topsoil and ground surface on which we stand. We do not generally see ourselves and our own activities as part of the processes we are trying to comprehend. But actually the Human Event Stratum is still being deposited. The traces of our own activities – the trenches, sections and other marks we leave in the ground – will be folded into it and become as much a part of the stratum as the material remains of ancient civilizations. In short, our view is only a partial and incomplete one, which Zalasiewicz’s futuristic vision helps us to transcend.
In envisaging a future encounter with the entire sequence of archaeological deposits as a single finite stratum sandwiched between layers of sedimentary rocks above and below, the book places archaeology in its geological and indeed its astronomical context (as exemplified by the picture on the cover). In providing such an all-encompassing perspective, it is not just of interest to geologists: it challenges and broadens the archaeological imagination too.
For archaeologists of contemporary material culture, a significant methodological problem is how to apply traditional methods and perspectives – developed for the study of ancient and buried material remains – onto the study of artefacts and buildings which are still in use. A reading of this book suggests that looking into the future can help us in looking back at the present and the past. The attempt to imagine how archaeological evidence might be represented in the geological record millions of years from now is an important thought experiment for archaeologists to undertake, following Zalasiewicz’s lead. It gives us an extra vantage point from which we can include the material remains of our own and recent times in the same cognitive categories as those of ancient civilizations, applying similar methods of archaeological reasoning to both.
For those interested in the emerging field of archaeology of space, the book neatly turns our perspective round. Instead of looking outwards into space from the surface of the planet, it looks inwards at the earth and its archaeological remains from an outside standpoint – that is, from the perspective of hypothetical alien visitors. This reflexivity is important. A search for traces of life on other planets, for example, must go together with an awareness of how material traces of our own civilizations might appear to other intelligent life forms. With this in mind, Zalasiewicz reminds us of the extraordinary character of the Apollo moon landing sites. Unlike archaeological sites on Earth, these are not subject to either erosion or burial, but are likely to remain in a more or less pristine state for millions of years.
Geology and archaeology traditionally maintain a curious distance from each other, operating for the most part on different timescales. The Earth After Us touches places where those two temporalities intersect, and in exploring these it crosses the disciplinary boundary in new and exciting ways. Archaeologists should read this book…