Rocks and oceans lead him back to ancient times
Donald Canfield uses chemistry and biology to study the Earth's past. His work often causes the rewriting of textbooks on the history of the oceans - and thus also the history of life. He is the 2023 recipient of the Villum Kann Rasmussen Annual Award in Science and Technology.
“I never want to hear you say that again!”
These were the words of Donald Canfield's supervisor at Yale University, Bob Berner, when Canfield, as a young, newly minted Ph.D. and frustrated at not being able to find a job, in 1988 announced that he did not want to waste his life as a jobless Ph.D. Instead, he would rather give up research and open a bicycle shop.
But it never came to a bicycle shop. A job did come along, and so did a lifelong research career for American-born Donald Canfield, who is today a Professor of ecology at the University of Southern Denmark.
Donald Canfield is dealing with some of the big questions about the history of the Earth:
What did the Earth look like billions of years ago, and why does it look different today? Why did life evolve the way it did, and how was it even possible? What interactions between chemistry, geology and biology make Earth such a living and dynamic place with vital elements like oxygen, nutrients and carbon constantly circulating in global cycles?
Cyanobacteria in the windowHe finds the answers in studies of rocks, in sediment samples from the seabed and riverbeds, in tanks with sea sponges and in trays with algae. Indeed, you can often find slimy green mats of cyanobacteria growing in plastic trays in his office window at the University of Southern Denmark. You also find his close colleagues at SDU, some of them he has known and worked with since his first visit in Denmark in 1990.
It was the sea that originally inspired Canfield to become a researcher – more specifically, an oceanographer. As a child he loved to look at the sea, to listen to it, to be in it, to go fishing with his grandfather in the Florida Keys, and to watch the famous oceanographer Jacques Cousteau on television.
The thing about the history of Earth is that there are so few constraints that any crazy idea can get some kind of credence. I didn't want to be that guy. I wanted to be the guy that thinks carefully about it and understands what is going on
Oceanography could not be studied at Miami University in Ohio, so Canfield chose chemistry. To him, there was something beautiful about the way molecules worked and reactions occurred. Fondness of chemistry turned into excitement when, at the age of 21, he took a course in environmental chemistry and met the lecturer Bill Green, who would become his close mentor and colleague for many years to come.
- He is the single biggest inspiration in my life. He was so not pretentious, just wanted to be called by his first name - he would fit in well in Denmark. He showed me that chemistry is also about what is happening here and now, says Canfield and elaborates:
- My first fieldwork was with him; we wanted to see if we could understand the formation of calcium carbonate in a small lake nearby – at the time there was a lot of interest in this because nobody really understood it. It was just a little nothing project, but I loved it! Wow!
Canfield and the ocean came closer
In the following years, Canfield and the ocean came closer. Fieldwork and expeditions took him to Alaska and Antarctica. His research interest also expanded to geochemistry, biochemistry, ecology and climate, and a question began to form in his mind:
What can be learned about the Earth's past by studying the processes taking place on Earth today?
- I was interested in going in that direction, but I wanted to do it with credibility. The thing about the history of Earth is that there are so few constraints that any crazy idea can get some kind of credence. I didn’t want to be that guy. I wanted to be the guy that thinks carefully about it and understands what is going on, so it became important to me to find the right people to learn from and work with.
Many researchers were already familiar with the connection between chemistry, biology and geology, the word biogeochemistry had already been introduced in the book The Biosphere by Vladimir Vernadsky in 1926, and in 1934 Lourens Baas Becking published the book Geobiology.
Elements of life forever in motion
But the field was still young and in Canfield's words, it had no real direction yet.
At Yale University, he was tutored by the outstanding geochemist Bob Berner, who tried to understand how the biological activity of microorganisms affected global element cycles, both now and through geologic time.
On Earth there are a number of cycles: sulphur, oxygen, carbon, nitrogen, phosphorus, iron, etc., that generate elements and compounds nourishing life on Earth. The chemical substances of the cycles are taken up by microbes, plants and animals and are excreted again, then deposited in sediments and turned into stone. The stone weathers down and releases the elements back to the environment. The elements are forever changing, forever in motion, but always following their own cycle.
- Berner was interested in reactants and end product, but not so much in the organisms that did the work.
First steps in Denmark
Something was missing, Canfield believed:
- People in my lab were not all that interested in the microorganisms doing the job. Were they common in nature or rare? Did they become more or less affective when working with other organisms? More or less active at different temperatures? How did they function in their natural environment, away from the laboratory? You need to know these things to get as accurate a picture as possible.
The collaboration with Berner got Canfield even more interested in the role of microorganisms in the element cycles, and his dedication to learn more about the Earth's bio-geo-chemical history grew.
Others were fascinated with this field, too. At Aarhus University, Bo Barker Jørgensen studied microorganisms in sediments and was an expert on their ecology.
Canfield's most important contributions 1 - Canfield Ocean
When Donald Canfield came to SDU in 1998 and was waiting for his laboratory to be built, he used the time to write one of his most significant papers, which was published in Nature: a new theory for the primeval ocean.
It was common knowledge that the Earth's atmosphere and oceans became oxygenated to something like today’s levels during the "The Great Oxidation" event 2.4 billion years ago.
Canfield, however, saw something different in the available evidence and suggested that Earth’s atmosphere did not reach full oxygenation and that the oceans remained largely oxygen free for the next 1.7 billion years. This ocean state of low oxygenation has since been called the Canfield Ocean.
In 1989 he invited Canfield to visit Aarhus. Barker Jørgensen had read a couple of Canfield's papers, (one on the sediment uptake of oxygen, and one on the iron cycle; what phases does iron take on its way through the cycle, how do organisms interact with iron?), and that led to two short visits in 1990-91, while Canfield was otherwise busy at NASA and Georgia Tech back home in the USA.
In 1993, Bo Barker Jørgensen started the Max Planck Institute for Marine Microbiology in Bremen and Donald Canfield was offered a dream job to come and work with colleagues with the same interest and enough money to do pretty much whatever they wanted.
The fascinating element oxygen
Microorganisms became essential tools to understand what had happened in the Earth's distant past, when, for example, a stone was formed. How much oxygen was in the air at that time? How much oxygen was in the oceans? How much sulfate was in the ocean water?- Today's microorganisms could tell us that. This allowed us to draw more and more detailed pictures of the Earth's early environment.
The large element cycles were also important for this research. Iron and sulfur cycles had been closely studied by Canfield, but one element particularly fascinated him: oxygen.
Earth is the only planet where oxygen is found in such large concentrations that it can support life as we know it today. But where does it come from and what role did it play in the evolution of Earth and life?
There was no oxygen in Earth's early atmosphere, but there was lots of nitrogen, hydrogen and carbon dioxide, spewed out by massive volcanic eruptions. 2.4 billion years ago, the atmosphere's oxygen levels increased significantly. How did that happen? The easy explanation (as Canfield calls it) is that blooming cyanobacteria got energy from photosynthesis and produced oxygen, which then rose and accumulated in the atmosphere.
Buried with dead organisms
But Canfield doesn't think it was quite that simple: if there were oxygen-producing organisms around, you would also expect oxygen-consuming organisms, and then no oxygen would be able to escape to the atmosphere.
Instead, he believes that some of the oxygen was stored in the sediments of the ocean floor in the form of buried dead organisms. From there, oxygen was released into the atmosphere. He believes that this complex dance between biology, chemistry and geology is what gave us oxygen in the atmosphere.
- Once there was oxygen in the atmosphere, it could begin to interact with rocks on the Earth's surface releasing critical elements like phosphorus and iron. The elements would act as nutrients in the oceans - and thus you have the beginning of a long series of chemical reactions that gradually changed the Earth's geo-bio-chemical signature to the one we know today.
Citizen Science and the democratizing of data
The collaboration with Bo Barker Jørgensen in Aarhus and Bremen was the start of a life in Denmark, where Canfield was hired as a professor at University of Southern Denmark in 1996.
Soon after, he became one of the leading forces behind the establishment of first, the Danish Center for Earth System Science and later, the Nordic Center for Earth Evolution, both funded by Denmark's National Research Foundation.
The exploration of Earth's history and especially the relationship between oxygen and animals is today a core area of Canfield's research, and he continues this work at SDU.
SDU is also the base of two new projects, both of which are focused on gathering more knowledge about the ocean, but also on – and this is equally important to him – democratizing access to data and involving people who are not researchers; citizen science.
- We need to map the ocean elements. There is so much we still don't understand, and we really don't have very many sediment samples to base our studies on today. My idea is to collect 5000 new sediment samples from all oceans in the world.
Canfield's most important contributions 2 - Animals and the chemistry of the oceans
When a worm or a crab burrows in the ocean floor, it performs bioturbation, meaning that the activity of living animals contributes to stirring the sediment and mud of the seabed to an extent that impacts the entire chemistry of the sea.
In a paper in PNAS, 2009, Canfield and his team show that 550-600 million years ago, living animals dug around in the ocean-bed to an extent that led to the oxygenation of the mineral pyrite. This led to raised levels of sulphate in the ocean water, and with time this was deposited as gypsym – one of the most common sulfate minerals in nature today. This paper helped raise the awareness that bioturbation can cause enormous environmental changes.
The ocean data that already exists are - according to Canfield - scattered and difficult to access. Some have been published in scientific literature, others are stowed away in not very user-friendly databases. Others are probably still sitting on a drive or in a desk drawer somewhere and haven't been published at all.
- The idea is to collect everything in an easily accessible database, that everyone can use, not only researchers, but also schools, etc. We need to democratize access to this data.
Along this project, for which he has already hired a data specialist, he has ambitions for a global citizen science project, where schools, local organizations and volunteers help collect water samples from rivers all over the world and send them back to him and his research team.
- Such water samples can reveal a great deal about the planet's carbon cycle and how it has evolved over time. This can be super exciting!
Earth will be fine. We can’t kill it
In the same way, as Canfield uses his science to learn more about environmental chemistry in the world around him, he also likes to share gained knowledge and insights with society.
He does so in interviews, in books (among others: Oxygen: A Four Billion Year History), and most recently in the play While the Sun Burns about the deep gap between the younger and the older generation's reactions to climate change, personified by a mother and a son played by Lotte Andersen and Louis Bodnia Andersen.
Together with two biologists, an astrophysicist and a philosopher, Canfield collaborated with the writing team on the creation of the play, which was staged at Teater Black/Hvid in Copenhagen.
Earth will be fine. There will be photosynthesis and plate tectonics moving mountains around and causing rain to fall from the atmosphere. Elements will cycle from land into oceans and back again. These things are fundamental. We cannot kill Earth
Personally, Canfield is not worried about the future of the planet. The future of mankind, yes; we need to change our way of living and reduce CO2 emissions so that future generations will not be left with unmanageable climate problems. But he is not worried about the future of the planet.
- Earth will be fine. We can’t kill it. There will always be organisms able to survive, no matter what we do to Earth. There will be photosynthesis and plate tectonics moving mountains around and causing rain to fall from the atmosphere. Elements will cycle from land into the oceans and back again. These things are fundamental. We cannot kill Earth.
Read about Donald Canfield's latest results
Canfield's most important contributions 3 - The evolution of animal life and oxygen
Most of us think that all animal life on Earth is so dependent on oxygen that oxygen and animals are inseparable partners: when there is not much oxygen on Earth, there cannot be animal life.
In a series of papers, Canfield and his team have shown that from about 1.7 to 1.0 billion years ago there was about 4% of todays’ levels of oxygen in the atmosphere. This doesn’t sound like much oxygen, but they further showed that the earliest animals, represented by sea sponges, did not need more oxygen than this to live.
As animals evolved some 700 million years ago, there was likely sufficient oxygen for early animals 1 billion years before animals evolved. In this case, factors other than oxygen likely controlled the timing of animal evolution.
Meet the researcher
Donald Canfield is Professor of Ecology, Head of Research, Department of Biology, University of Southern Denmark Author of more than 350 scientific papers, cited nearly 55,000 times Member of the Royal Danish Academy of Sciences and Letters, Royal Swedish Academy of Sciences, Royal Society of London, National Academy of Sciences (US). Fellow, American Geophysical Union, Society for Microbiology, Geochemical Society and American Academy for the Advancement of Science (AAAS) Chair, Danish Institute for Advanced Study (DIAS) Villum Investigator Recipient of the Vladimir Vernadsky Prize (2010), the Urey Prize (2011) and the Order of the Dannebrog (2021) Married to Marianne Prip Olsen. Together they have the children, Lind Prip Canfield (27) and Ellen Prip Canfield (22).