Countless lakes in Canada and elsewhere may offer some important insights into how life on Earth began and may also help us grapple with the pressing environmental issues facing the planet today.
The Boreal Shield is the the largest of Canada’s 15 terrestrial ecozones, where boreal forests overlap the Canadian Shield. It stretches almost 4,000 kilometres from Newfoundland to Alberta. The millions of lakes that stud the Boreal Shield may offer clues into how ancient microorganisms might have shaped atmospheric and geological conditions on Earth.
We’ve long been fascinated by how life on Earth began. From an evolutionary perspective, we can trace our origins back billions of years to single-celled microorganisms in the ocean.
The conditions of this early Earth ocean of the Archaean Eon, more than 2.5 billion years ago, were very different from ocean conditions today. The oceans lacked oxygen and were high in iron; many now speculate that ancient bacteria might have eked out an existence on a mixture of iron-rich chemicals and light energy.
One way to investigate the mysteries of Earth’s origins is to look for modern-day equivalents of these ancient oceans and examine their chemical processes and biological diversity. The challenge, however, is that modern equivalents of ancient oceans are extremely rare.
Lake Matano in Indonesia is an example of one such modern equivalent. It’s an iron-rich lake that has permanently oxygen-free bottom waters. These bottom waters are sufficiently deep and wind-protected that they do not mix with surface waters throughout the year.
In Lake Matano, and a select few other lakes discovered in recent years, specific species of “green sulfur bacteria” are thought to thrive by using light energy to support a metabolism based on dissolved iron.
Could these bacteria represent modern-day equivalents of the earliest metabolisms on Earth? Did similar ancestors of these bacteria shape our biosphere to help support the evolution of additional life forms? What other microorganisms and metabolisms associate with these species? Could these too represent the earliest processes on the planet?
Oxygen and green sulfur bacteria
The Lake Matano discoveries had special significance for Dr. Sherry Schiff in the Department of Earth and Environmental Sciences at the University of Waterloo. Her long history of studying freshwater habitats, including those at the International Institute for Sustainable Development — Experimental Lakes Area (IISD-ELA) in northern Ontario, helped her formulate a hypothesis.
Modern equivalents of the early Earth ocean are anoxic, iron-rich and sulfur-poor. Millions of Boreal Shield lakes come very close to these conditions.
The problem is oxygen.
Many of the Boreal Shield lakes in Canada, and boreal lakes across Europe and Russia, are high in iron and low in sulfur, yet exposed to oxygen at most depths at least twice a year, when the lake surface waters mix with deeper waters. If the green sulfur bacteria return following exposure to oxygen, then Dr. Schiff predicted that millions of Boreal Shield lakes could harbour microbial communities analogous to those of Earth in its infancy.
And if IISD-ELA lakes were among these examples, then many of these Canadian lakes could be manipulated experimentally for further study.
In order to test these predictions, Dr. Schiff assembled a team of Earth scientists, limnologists (freshwater scientists) and microbiologists.
The Earth scientists looked at the chemical composition of representative IISD-ELA lakes at varying depths and at different times, and the microbiologists, led by Jackson Tsuji in Dr. Josh Neufeld’s lab, helped generate a census of microbes in these same samples by analyzing extracted DNA.
The chemical data indicated that an iron-based metabolism, energized by light, was likely. The DNA data confirmed that species of green sulfur bacteria almost identical to those in Lake Matano became abundant when oxygen was depleted in the lakes.
Implications for human health
In addition to providing a unique opportunity to study Canadian Boreal Shield lakes as examples of the oceans of early Earth, this important new discovery has potential implications for environmental issues today.
The occurrence and severity of toxic blooms of cyanobacteria may be tightly linked to the availability of iron. In addition, microbial metabolism of iron may well be linked to the metabolism of other compounds of interest, including phosphorous, mercury and the potent greenhouse gas, methane. Each of these compounds has major implications for our climate, aquatic systems and for human health.
The discovery that millions of Boreal Shield lakes are potential examples of early Earth oceans was not a predictable outcome of the original research initiative. That the researchers had the flexibility and funding to pursue some unexpected results that lead to this crucial interdisciplinary research was fundamental to their success.
The results have broad implications for our understanding of early Earth origins, including the origins of life on the planet, in addition to modern-day relevance. All of it underlines how basic research can lead to unexpected discoveries.
Future research by the Schiff and Neufeld labs, as well as collaborators at Wilfrid Laurier University, the University of Toronto and the IISD-ELA, will explore the links between Boreal Shield lakes, cyanobacteria, methane, phosphorous and iron.
At this point there are more questions than answers, but that’s how science works.
Josh D. Neufeld, Professor, University of Waterloo; Jackson Tsuji, PhD student, Neufeld Research Group, University of Waterloo, and Sherry Schiff, Professor, Environmental Geochemistry, University of Waterloo