In a remote area in the Yukon wilderness in Canada, a team of researchers from Stanford University have made an incredible discovery. A rich vein of fossils and rocks from the Paleozoic period have been unearthed here, touted to be the most diverse and richest source of evidence showing organisms evolved during the most crucial period for life on Earth. 

An international team of researchers have discovered a huge collection of fossils and rock samples dating back to the Paleozoic period. Uncovered along the banks of the Peel River, a few hundred miles south of the Arctic’s Beaufort Sea, the records show a near 120 million year history of the time when life on earth flourished, leading to rapid changes in the complexity of life and multicellular organisms. 

“It’s unheard of to have that much of Earth’s history in one place,” said Stanford University geological scientist Erik Sperling, lead author of a July 7 study detailing the team’s findings in Science Advances. Most rock formations from the Paleozoic Era have been broken up by tectonic forces or eroded over time. “There’s nowhere else in the world that I know of where you can study that long a record of Earth history, where there’s basically no change in things like water depth or basin type,” he added in a Stanford media release.

The Paleozoic period marked the rise of oxygen from the ocean floor, a very important development in the history of life evolving on planet Earth. Before this, oxygen was a scarce resource and this allowed only unicellular organisms to inhabit oceans of the past. However, with the dawn of the Paleozoic era 541 million years ago, there were small upticks in oxygen levels. The birth of the Devonian (an interval of the Paleozoic Era), roughly 405 million years ago, saw an explosion in oxygen levels in just a few million years. The oxygen levels during this period rose to near-modern levels, allowing complex life to blossom. In fact, this period in the Paleozoic birthed big predatory fish in our oceans, huge ferns and conifers replaced algae in dominant land masses and complex insects like Dragonflies took flight.

Impact of findings

This finding is of tremendous importance, especially in 2021, where we are all aware of the dramatic effects climate change and the mass extinction of species are having on the planet. The increasing frequency of large-scale natural disasters is pushing researchers to understand how the earth adapts to sudden change. Something that has been periodic throughout history. It is well known to scientists that the “Cambrian explosion of life and the first of Earth’s big five mass extinctions, about 445 million years ago at the end of the Ordovician,” are extremely important events that we do not know much about. Most of the understanding we have is derived from the most plausible theories and dating the fossils we find across the globe. But the evidence is so scattered and tough to extract that we do not have an accurate picture of the timeline of this explosion of life. 

“In order to make comparisons throughout these huge swaths of our history and understand long-term trends, you need a continuous record,” said Sperling, an assistant professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). This is where this finding comes in handy. The fossils and the rock sediments found in Canada are giving researchers a near 120-million year view of how life during this period was birthed, morphed, and thrived.

Method of study

This discovery was not easy. Identifying the region as one of the oldest remaining untouched ecosystems on earth, the team has spent three years at the Peel river site collecting samples from more than a mile of interbedded layers of shale, chert, and lime mudstone. This expedition involves carefully extracting possible rock samples and fossils embedded in them in a dense and hard-to-reach area of the Canadian wilderness.

“We spent a lot of time splitting open rocks and looking at graptolite fossils,” Sperling said in the article. According to him, the tiny markings (described as pencil-like), left by fossils of these early sea creatures, give geologists a way to date the rocks in which they’re found.

Once the researchers had finished identifying and dating graptolite fossils, they ground the rocks in a mill, then measured iron, carbon, phosphorus, and other elements in the resulting powder to assess the ocean conditions at the time and place where the layers formed. They analyzed 837 new samples from the Peel River site, as well as 106 new samples from other parts of Canada and 178 samples from around the world for comparison.

What do the findings show?

The most important takeaway from the discovery is the understanding of oxygen levels during this period. Our previous understanding of how and when oxygen was released into the earth’s atmosphere has changed, thanks to the team. New data shows that the period of  low oxygen levels, or anoxia, “likely persisted in the world’s oceans for millions of years longer than previously thought – well into the Phanerozoic when land plants and early animals began to diversify.”

“The early animals were still living in a low oxygen world,” Sperling said. Contrary to long-held assumptions, the scientists found Paleozoic oceans were also surprisingly free of hydrogen sulfide, a respiratory toxin often found in the anoxic regions of modern oceans.

The emergence of complex plant life (like giant ferns and coniferous trees of the ancient world) is a great indicator of a spike in oxygen levels. Like we know, plants play a major role in the oxygenation of the planet. These include seaweeds, phytoplankton, and algae, which contribute towards adding new oxygen by consuming carbon dioxide. The small spikes in oxygen levels in the early Paleozoic period could have triggered new, more complex plant matter first. This could have then exponentially flooded our atmosphere with the gas that supports all life on earth.

“There’s a ton of debate about how plants impacted the Earth system,” Sperling said. “Our results are consistent with a hypothesis that as plants evolved and covered the Earth, they increased nutrients to the ocean, driving oxygenation. In this hypothesis, the influx of nutrients to the sea would have given a boost to primary productivity, a measure of how quickly plants and algae take carbon dioxide and sunlight, turn them into new biomass – and release oxygen in the process.”

The fossils show that this oxygenation triggered the mass-extinction of graptolites, which evolved and thrived in a planet with very low oxygen levels. The sudden change “probably killed off graptolites. Although more oxygen is really good for a lot of organisms, graptolites lost the low oxygen habitat that was their refuge,” Sperling said. “Any environmental change is going to have winners and losers. Graptolites might have been the losers.”

Impact of findings

This shows us that life is resilient but new changes bring with it a massive loss of current life, making way for life more suited to the changes that the ecosystem presents. Our planet hosts life that has gone through a huge amount of metamorphosis in a relatively short period. The evolution of modern-day humans has triggered such a great change in the landscape in just 200-300 thousand years. Think about this – language was developed approximately 50,000 years ago. Since then, man has made such gargantuan leaps in technology that has completely changed Earth and affects all life on it. I think that a more acute understanding of such sudden changes in the past, the timeline of adaptation, and how life finds a way through might be the push we need to understand our role on Earth.