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Earth systems: Shaped by life

Wolfgang Lucht sees a lesson for humanity's future in the long co-evolution of our planet and its inhabitants.

Revolutions That Made the Earth

Oxford University Press: 2011. 448 pp. £29.95/$52.95 9780199587049 | ISBN: 978-0-1995-8704-9

Earth has life written all over it: in its sediments and soils, its atmosphere and its oceans. Without life, the planet's chemical state, energy balance and history cannot be understood. In Revolutions That Made the Earth, Earth-systems scientists Tim Lenton and Andrew Watson describe the shaping of our planet by life, combining evolutionary biology and geochemistry to do so.

Lenton and Watson relate how life forms have co-evolved with the planet's environment over billions of years, and suggest explanations for some of the mysteries in the geological record. They focus on two major events that transformed Earth. Both were caused by innovations in the biological realm that were difficult to achieve in evolutionary terms, and both boosted the use of energy and recycling of materials crucial to life.

The first event is the oxygen revolution, triggered by the emergence of oxygenic photosynthesis more than 2.7 billion years ago, possibly in cyanobacteria. That led to the 'great oxidation' 300 million years later, when Earth's atmosphere retained oxygen for the first time — the greatest chemical alteration in the planet's history.

Earth was transformed by the emergence of oxygen-producing photosynthetic organisms — such as the cyanobacteria found in these ancient stromatolites. Credit: J. READER/SPL

The second is the complexity revolution that began around 1 billion years ago with the rapid rise of eukaryotic life — cells with nuclei that now make up all plants and animals. It allowed the conquest of land and the advance of complex multicellular life forms in the Cambrian explosion 542 million years ago, with profound geochemical consequences for the flows of carbon dioxide, oxygen and phosphorus that led to the planet we inhabit today.

Lenton and Watson are propelled by more than intellectual curiosity. By understanding previous planetary revolutions, they propose that we might be able to draw cautious conclusions about the upheavals that humans are currently causing on Earth by melting its ice caps and deforesting its surface. They suggest that our ability to communicate through language, and to create extensive cultures through the networking of our messages, can be seen as the unfolding of another rare and hard-won revolution in the history of life — a shift in global consciousness.

Earlier transitions, the authors show, were followed by periods of turmoil in the Earth system, caused by instabilities inherent to its complex behaviour. There was no guarantee that life would survive these fluctuations: runaway effects twice locked Earth into global glaciations when greenhouse-gas concentrations plummeted. They could have turned Earth into a heated desert when they ended. But over tens of millions of years, feedbacks established chemical cycles of carbon and oxygen that once more kept Earth within a corridor of habitability. Crises thus arose separately from meteorite impacts and volcanic activity.

The message for our time is that the current planetary state could equally be destabilized if human activity causes critical Earth-system thresholds to be passed. With enough warning and insight, we might avoid or limit the damaging changes, or adapt to them rather than simply suffering the consequences. But the current lack of progress in mitigating climate change and preserving complex ecosystems is not promising.

Lenton and Watson highlight two concerns. First, when Earth is operating near a tipping point, small changes in the driving factors can tip it rapidly from one state to another. We do not know how much the radiation balance of the atmosphere, or the ecological richness of ecosystems, or the chemical state of the oceans can be altered before cascades of effects are set off. Human activity could trigger a switch in important Earth-system processes even though the underlying change is gradual.

Their second observation is that former revolutions left life using more energy, with increased flows of materials from the environment, recycling of essential elements through life and increased networking of biological information. The authors extrapolate that for human societies to remain viable while using large amounts of energy to process large volumes of matter and maintain densely populated landscapes — as we do today using fossil fuels — we will have to boost the rate of recycling. The consciousness revolution must be followed by a recycling revolution.

Lenton and Watson's thought-provoking book is the latest in a distinguished line of works that have altered our perception of the planet. Russian–Ukrainian geochemist Vladimir Vernadsky first discussed the deep involvement of life in planetary chemistry in his 1926 book Biosfera (Biosphere). In Gaia (Oxford University Press, 1979), James Lovelock brought the self-stabilizing mechanisms of life into view by seeing the planet as a partially self-regulating, living whole. And Hans Joachim Schellnhuber's book-length chapter in Earth System Analysis (Springer, 1998) laid out a blueprint for a scientific discipline concerned with the interplay of social and environmental dynamics.

The inventor R. Buckminster Fuller proposed in the 1950s to construct a giant globe of light bulbs to display data sets of global phenomena. His idea was that an external, physical realization of world mechanisms would engage our minds and change our ecological perspective. He was convinced that if we did not become an active, consciously reflective part of planetary evolution, we would become an unwitting, passive part of it.

Lenton and Watson's Earth — shaped by life, an escapee of close calls and again on a perilous course in the wake of biological innovation — is a similarly novel depiction. The Copernican revolution had no direct effect on people's everyday lives, but it ushered in a new era of self-consciousness. Perceiving Earth as a complex system of co-evolution similarly alters our outlook.

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Lucht, W. Earth systems: Shaped by life. Nature 470, 460–461 (2011). https://doi.org/10.1038/470460a

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