"When life got big"
For the past 20 years, Queen’s paleontologist Guy Narbonne has been pushing the boundaries of what we know about the origin of complex life on earth. A world-renowned specialist on the origin of animals, he uses field work and a combination of sophisticated biological and geological techniques to interpret the remains of the oldest animals and their ancestors.
We know now that life first appeared on Earth about 3.5 billion years ago and remained simple and unicellular for the first three billion years of that evolution. Dr. Narbonne’s research is focused, as he says, on “when life got big” – the sudden appearance in the geological record of large, complex life forms among animals, plants and several failed experiments in life during the newly named Ediacaran Period, between 645 and 540 million years ago. To put that in context, that’s nearly eight times older than Tyrannosaurus rex and tens of millions of years older than the trilobites and other Cambrian fossils that paleontologists once regarded as the oldest fossil evidence of complex life.
In contrast with normal fossils – like the bones of dinosaurs and the shells of Cambrian sea life – all early complex life forms were completely soft-bodied and preserved under sand and silt as fossil impressions on the ancient sea floor. Finding them requires specialized search techniques that differ from those used in more traditional paleontology. This is why the apparent lack of complex ancestors of Cambrian life perplexed the great Charles Darwin – who admitted as much in The Origin of Species – and why their presence remained largely unknown until the mid-20th century. Narbonne’s discoveries have been critical in providing images of these earliest complex life forms and a plausible explanation for their sudden – geologically speaking – appearance. Together, they have helped to resolve “Darwin’s Dilemma.”
The evidence for this explanation has been gathered from sites around the world. In northwest Canada, Guy Narbonne, Hans Hofmann from Université de Montréal and Jim Aitken of Geological Survey of Canada discovered dime-to-loonie-sized disk-shaped fossil impressions 645 million years old that are among the oldest convincing candidates for early multicellular life. On Newfoundland’s Avalon Peninsula, Narbonne and Jim Gehling of the South Australia Museum discovered two-metre-long fossilized fronds which, at 580 million years old, represent the oldest evidence of complex multicellular life known anywhere in the world. Studies of the rich fossil outcrops there employed biological techniques never before applied to the fossil record to shed light on the ecology of fossil communities more than half a billion years old. The studies also allow the fossils to be compared to living communities today.
Narbonne’s description of the bizarre fractal architecture that characterized these early Ediacaran life forms – published in a cover story in Science magazine in 2004 – was heralded as one of the top 100 science discoveries that year. Later, working in southern Africa with colleagues from M.I.T., Narbonne discovered that these soft-bodied experiments in early complexity continued until the “Cambrian Explosion” – the nickname given to the remarkably swift evolution of skeletal animals 540 million years ago. That revelation was honored in a Namibian postage stamp issued in 2008.
All of Narbonne’s fossil studies have been integrated with state-of-the-art techniques in geology, biology, and chemical oceanography to deduce the evolutionary and environmental conditions that led to the origin of biological complexity. For instance, studies with his Queen’s University colleagues Noel James, Bob Dalrymple and Kurt Kyser elucidated key features of the massive ice ages that wracked pre-Cambrian Earth up until the first appearance of complex life. Another Narbonne study, completed in northwest Canada with Andy Knoll and Jay Kaufman of Harvard, was the first to integrate the early evolution of biological complexity with changes in the chemical composition of seawater during the Ediacaran Period. Narbonne’s studies in Newfoundland utilized cutting-edge geochemical techniques (developed by Don Canfield of the University of Southern Denmark) to show that the first appearance of large, complex life forms precisely corresponded with a major rise in free oxygen in the oceans and atmosphere, and provided a possible reason why “life got big” 580 million years ago.
Narbonne’s discoveries have resulted in numerous papers in Science, Nature and other key international scientific journals. His keystone paleontological discoveries and documentation of Mistaken Point in Newfoundland also led to the construction of a million-dollar fossil interpretation centre at the site and to Mistaken Point being listed as a potential UNESCO World Heritage Site. Among his many international duties, Narbonne is a member of the NASA Astrobiology Institute and a theme leader and scientific board member of the UNESCO International Geoscience Program. At Queen’s, he’s best known for teaching his first-year History of Life course to students from nearly every department across the university.