Crafoord Prize: The man who can explain the first 3 billion years of life on Earth
This story is the story of Earth – how the planet went from a rock covered in oceans of magma tossed about by comets and meteors to a green and blue orb teeming with life. Between those inhospitable beginnings and today, continents have formed and torn apart, mountain ranges have come and gone, ice caps have spread and receded. These are the lost worlds that Knoll has explored and brought to light.
“Having your nose against the rocks. There’s no substitute. If you’re interested in the history of this planet, the library is rocks,” said Knoll, who is Fisher Professor of Natural History at the ‘Harvard University.
The honor is for his work illuminating the first 3 billion years of Earth’s history, determining the age of bedrock layers, discovering tiny organisms from the depths of time that are the infinitesimal ancestors of each of us and the explanation for the world’s worst mass extinction. .
“He really tries to integrate all the available data – geological, biological and chemical and puts things into perspective. It’s not just a person who looks at a fossil and says, ‘Oh, that’s it and that’s it. came from this period,” said Daniel Conley, professor of biogeochemistry in the department of geology at Lund University in Sweden.
“He is able to make this holistic picture, to understand why the fossil is there and the context of everything that is happening at the time,” said Conley, a member of the Royal Swedish Academy of Sciences and the prize committee. Crafoord. in Geosciences.
It’s not necessarily the glamorous side of paleontology – Knoll primarily finds and examines microfossils visible only under a microscope, not the towering skeletons of extinct giants that take center stage in museum atriums. But the way he pieced together the story of Earth’s birth and early life revolutionized the field.
“Dinosaurs are (a) very, very small part of the record in terms of fossils and in terms of the times in which they exist. They’re amazing. I agree with that. But they’re just a small part of a much, much bigger story,” Knoll, 70, said.
The “boring” billion years
Our familiar world of complex animals began to take shape around 540 million years ago, during what is known as the Cambrian Explosion. But Knoll’s discovery of microscopic fossils of bacteria-like organisms, single-celled protozoa and algae that date back 3 billion years – and the environment in which they emerged – showed that the evolutionary path to our modern animal and plant life began much earlier.
“He was able to make these discoveries that there was life before we knew it,” Conley said.
Knoll put it this way: “We live on a microbial planet. Animals are really the icing on the evolutionary cake, but bacteria are the cake.”
Knoll also first described what is sometimes called the “boring billion” – a period in Earth’s history around 1.8 billion to 800 million years ago when nothing seemed to be happening. biologically or climatically. Nonetheless, he said it was a pivotal time that paved the way for life as we know it.
“Our work and that of others demonstrates that this is when the eukaryotic cell came of age – all of the molecular and cellular biology that ultimately made animals possible, was hammered out in that boring billion “, Knoll said.
Knoll said he was first mesmerized by the fossils he found growing up in the Pennsylvania Dutch country at the foot of the Appalachians.
“I remember that feeling when I was 12 and just the thought that you would break that rock and see something that no human being has ever seen.”
“It was a wonderful, wonderful thought, and I always get excited if I discover something or have an idea that no one else has had.”
He also applied his knowledge of Earth’s early evolution to Mars, interpreting data and images returned by the Mars rover Opportunity, which was active on the Red Planet’s surface from 2004 to 2018.
For Shuhai Xiao, a geobiology professor at Virginia Tech and a doctoral student under Knoll in the 1990s, it’s his former adviser’s work on Earth’s carbon cycle – and how it played a vital role in the changing cycles of the history of the planet — — who was the most influential.
“It opened the floodgates. Today we take that for granted and a lot of people use carbon isotopes to talk about the paleo environment. But that was 1986, and few people even did that kind of thing. analysis, let alone apply it to understand Earth’s history,” said Xiao, who has spent many hours with Knoll on long train journeys in China, travel to fossil sites.
“When I was on the pitch with him for the first time, I was very impressed.
Falling CO2 levels have turned Earth into a snowball twice, completely covered in ice, and greenhouse gas emissions from volcanic activity have warmed it again.
“Life relies heavily on carbon. It’s a unique element that can give rise to the molecular complexity that characterizes life, but it’s also particularly important to environmental history. The reason it heats up in right now is that we’re moving a lot of CO2 into the atmosphere,” Knoll said.
Knoll also offered the most credible explanation for Earth’s third and greatest mass extinction, when over 90% of species in the ocean disappeared and 70% of land animals became extinct. The event eventually paved the way for the rise of the dinosaurs.
Known as the “Great Dying”, it marked the end of the Permian period 252 million years ago, and its cause had long been debated. Theories included rising oceans, a cooler climate or even an asteroid like the one that later doomed the dinosaurs 66 million years ago.
The biological disaster unleashed at that time was frightening, Knoll said. On exposed rocks on the mountainside in China called Meishan, where Knoll worked, limestone rocks bristle with fossilized sea life, then after a point no wider than a knife’s edge, they all disappear, he said. he declares.
Perplexed by the phenomenon one night while awake tending to his son, Knoll had the idea that the apparent disappearance of life could have been due to a rapid increase in CO2. To figure out what might have happened, Knoll and his colleagues dug into the fossil record and divided the marine fauna that lived in the late Permian into two groups: vulnerable and CO2 tolerant.
For example, animals with gills for gas exchange should be more tolerant, while corals – which have carbonate skeletons – did not respond well. The group with the most CO2-tolerant traits, like clams and snails, largely survived the mass extinction.
“To the extent that we did something original was that there were all these geological explanations for the mass extinction then, and I was always struck by the fact that nobody really had looked at the fossils. I felt like a detective trying to solve a murder.”
The cause of the increased CO2 was eventually determined to be a massive area of volcanic activity in what is now Russia known as the Siberian Traps.
Resonance with today
While the current increase in CO2 is largely due to fossil fuel burning, not large-scale volcanic activity, Kroll said “there’s a very interesting resonance between the extinction patterns we see at the end of the Permian period and the kind of biological effects emerging from 21st century global warming.”
Studying past mass extinctions also shows that life bounces back, Knoll said, but it takes a very, very long time — tens of millions of years.
“You stand here in the physical and biological legacy of 4 billion years,” Knoll wrote. “You walk where trilobites once slithered over an ancient seabed, where dinosaurs roamed gingko-covered hills, where mammoths once towered over a freezing plain.
“It used to be their world, and now it’s yours,” he continued. “The difference between you and the dinosaurs, of course, is that you can understand the past and envision the future. The world you inherited isn’t just yours, it’s your responsibility. What happens next? up to you.”