Life has influenced Earth’s atmosphere going back billions of years. But until two centuries ago, when humans started burning fossil fuels on an industrial scale, the most significant living climate controllers were organisms invisible to us: single-celled microbes. Small but mighty, microorganisms are nature’s chemists. At the very bottom of all biological processes, microbes break down, transform and supply the nutrients required for life and bring elements into biochemical cycles across the planet — atmosphere, ocean, earth and biosphere.
“The microbial biodiversity that we do not see with our naked eye sustains the biodiversity that we do see,” said Tom Battin, an environmental scientist who studies microbial ecology at the Federal Polytechnic School of Lausanne. “The microbes are like the conductors of the biogeochemical Earth orchestra. They make the music.”
Microbes convert inert nitrogen and phosphorus, for example, into forms life can use to build DNA molecules. They are responsible for at least 50% of global photosynthesis, which removes carbon dioxide from the atmosphere. They also return carbon dioxide to the atmosphere when breaking dead organisms down into their constituent molecules. As microbes drift into the deep sea, they bring carbon with them, storing it as sediment and then, deeper in the earth, as rock. The cells are even found in clouds, where they act as seeds around which ice crystals form.
“I wish people were aware of this invisible world that is working like mad behind the scenes,” said Lisa Y. Stein, a climate change microbiologist at the University of Alberta. “Plants, microbes, water, air — it’s all one system working in synergy.”
Microbes’ planetary effect dates back to life’s origins, when ancient cells first began emitting methane, a greenhouse gas that likely warmed Earth’s early atmosphere. Then around 2.7 billion years ago, in a major transition for the planet, chlorophyll-based photosynthesis evolved in cyanobacteria, which gained the ability to use sunlight to make sugar out of carbon dioxide and water — and released oxygen as a byproduct. Over hundreds of millions of years, microbes’ oxygen emissions filled the atmosphere, causing the extinction of most anaerobic life while creating the conditions for the emergence of land plants. Those plants went on to transform a mostly dead landscape into a paradise for large, complex life forms like us.
Throughout the history of life on Earth, microbes have acted as master regulators of our planet’s climate system. But now we have overpowered microbes’ climatological effects. On this warming planet, with greenhouse gas emissions rising at dangerous rates, microbiologists argue it’s time to better value our invisible colleagues. And as fellow regulators of Earth’s climate, we must understand how our actions affect microbes and learn how to work with them.
These short stories about scientists working at the leading edge of climate microbiology reveal the vital role microbes play in our biosphere and climate system, and illuminate new possibilities for collaborating with these incredible natural chemists.
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