Of Microbes and Planets

Understanding the deep history and dynamics of our planet is not an easy task: the earth escapes our attempts to visualise and characterise it. It exceeds our limited understanding and overflows the scales we are used to. Yet, people have tried to figure out our place in the universe and the functioning of the planet since time immemorial. Scientists have only recently begun to wrap their heads (and their instruments) around the planet and its complexity. The experiences of micropaleontology at sea were instrumental in this effort because they helped reveal the planetary influence of biological processes on Earth systems. In fact, the dominant model of disciplinary divisions between sciences that consolidated over the course of the 19th century had traditionally separated the geophysical and chemical hard sciences and their technoscientific applications from the softer sciences of life. The earth was treated as a backdrop on which life took place. Even though studies of microbial worlds, such as the work of Sergei Winogradsky and Vasily Dokuchaev on environmental microbiology and soils, had offered alternative visions, they remained marginal, not least due to intellectual and socio-political divisions.² Despite this marginalisation, research on the relation between biological and geochemical processes was profoundly influential in the successful diffusion of early systems theories in biology and beyond. Such approaches proved particularly useful for technological application and quickly led to the wartime implementation of cybernetics (famously, for instance, in the development of anti-aircraft technologies).³ In the postwar period the interconnection between biological and earth systems gained even more traction in scientific research. The hybrid field of biogeochemistry began to bridge the traditional divide between geophysical sciences and biology, providing the foundations of ecology with an understanding of the complex relations shaping the planet.⁴

Yet, most of the early works in ecology relied on limited experimental settings, using small, enclosed environments for research, like Evelyn Hutchinson’s studies of Linsley Pond.⁵ This is also why oceanography, with its ‘big science’ appeal and its global scale, proved to be an incredibly successful field in which to ask biogeochemical questions. In combination with postwar science and its fascination with outer space, the study of the world’s oceans effectively expanded biogeochemistry to provide a tool that could encompass (and in turn shape) the planetary scale.⁶ The efforts in deep sea drilling produced growing numbers of records which are accumulated in museums and other scientific collections, including the Lamont-Doherty Collection. While also contributing to mineralogical and geophysical studies and collections, these materials – most importantly – highlighted the centrality of microbial life for regulating the habitability of Planet Earth.⁷ Combined with advances in microscopic media and our understanding of the molecular workings of life, these studies formed two fundamental arguments: firstly, that microorganisms should be considered to be the ancestors of all life on our planet, and secondly, that they determine and mediate the geochemical cycles on which life depends. As such, they provide an important record of the changing conditions of our planet. This offered the basis, for instance, for Hays, Imbrie, and Shakleton’s milestone paper published in Science in 1976, demonstrating the impact of planetary dynamics on ice-age cycles by using Cycladophora as a biomarker of paleotemperatures.⁸

In the 1970s, the view of microorganisms as ancestors of all life and their metabolic role in all sorts of physico-chemical processes converged in the formulation of the controversial Gaia hypothesis by NASA scientist James Lovelock. The hypothesis proposes that living organisms interact with inorganic physicochemical planetary systems to form an integrated, self-regulating system that maintains the conditions of habitability on Earth.⁹ The role of microorganisms in this system was stressed especially through Lovelock’s collaboration with microbiologist Lynn Margulis, famous for her pioneering proposal of how cells evolved through endosymbiosis.¹⁰ While some critics view Gaia as a new-age personification of the planet, Margulis pointed out how the self-regulatory character of the system is in fact better understood as an emergent property caused by the interactions between organisms on a planetary scale. Thus, the Gaia hypothesis gained much support, also thanks to its traction in popular science and the countercultural movement. Yet, more official scientific circles remained skeptical, in part also because of the unconventional character of Lovelock and Margulis and the success the hypothesis had with counter cultural movements.¹¹ Yet, more evidence pointing at the planetary impact of microbial life has accumulated since the 1970s. An important example is the characterisation of what is commonly known as the Great Oxygenation Event. This refers to an essential episode in the biogeochemical history of the planet, which saw a shift from an oxygen-poor to an oxygen-rich atmosphere. Without this event, life as we know it would not be possible. And while scientists still debate the details of how exactly this shift took place, it is clear that microorganisms – in particular cyanobacteria, also known as blue-green algae – had a key role in it, radically altering the atmospheric composition of our planet. Today, most of the oxygen in our atmosphere continues to be produced by photosynthetic microorganisms living in the ocean, such as diatoms.¹²

The history of how we slowly came to recognise the importance of microbial life for our planet and its dynamics still continues. Microbes – and their deep evolutionary histories – are entangled in the fabric of our planet, and they are crucial to making life on Earth last. Even though microbes remain often marginal to our understanding of the world, their planetary histories show how they continue to be a vital part of our lives.