Aurelia Butler
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In the wake of history’s deadliest mass extinction, ocean life may have flourished
Following the most severe known mass extinction in Earth’s history, vibrant marine ecosystems may have recovered within just a million years, researchers report in the Feb. 10 Science. That’s millions of years faster than previously thought. The evidence, which lies in a diverse trove of pristine fossils discovered near the city of Guiyang in South China, may represent the early foundations of today’s ocean-dwelling ecosystems.
The conventional story was that the ocean was kind of dead for millions of years after this mass extinction, says paleontologist Peter Roopnarine of the California Academy of Sciences in San Francisco, who was not involved in the research. “Well, that’s not true. The ocean [was] very much alive.”
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The Great Dying, or Permian-Triassic mass extinction, occurred around 251.9 million years ago, at the end of the Permian Period, after a series of massive volcanic eruptions (SN: 12/6/18).
“The oceans warmed significantly, and there’s evidence for acidification, deoxygenation [causing widespread dead zones], as well as poisoning,” says Roopnarine. “There [were] a lot of toxic elements like sulfur entering into parts of the ocean.”
Life in the seas suffered. More than 80 percent of marine species went extinct. Some researchers have even proposed that entire trophic levels — castes in an ecosystem’s food web — may have vanished.
Figuring out how long life took to fully recover in the wake of all that loss has been challenging. In 2010, researchers studying fossils from the Luoping biota in China proposed that complex marine ecosystems fully rebounded within 10 million years. Later, other fossil finds, such as the Paris biota in the western United States and the Chaohu biota in China, led scientists to suggest that marine ecosystems reestablished themselves within just 3 million years.
Then in 2015, a serendipitous discovery narrowed the gap again. Paleontologist Xu Dai, then an undergraduate student at the China University of Geosciences in Wuhan, was studying rocks from the early Triassic during a field trip near the city of Guiyang, when he split open a piece of black shale. Within the rock, he discovered a surprisingly well-preserved fossil of what would later be identified as a primitive lobster.
The arthropod’s immaculate condition sparked a series of return trips. From 2015 to 2019, Dai, now at the University of Burgundy in Dijon, France, and his colleagues uncovered a bricolage of fossilized life: Predatory fish as long as baseball bats. Ammonoids in swirled shells. Eel-like conodonts. Early shrimps. Sponges. Bivalves. Fossilized poo.
Fossilized coelacanths (one shown here), a type of bony fish, are the largest macrofossils yet found in the Guiyang biota.Dai et al/Science 2023
And the prizes kept coming. Both under and within the Guiyang biota, Dai and his colleagues discovered beds of volcanic ash. An analysis of the amounts of uranium and lead in the ash revealed that the Guiyang biota contained fossils from roughly 250.7 to 250.8 million years ago (SN: 5/2/22). The dating was further supported by the types of fossils found and by an analysis of the different forms of carbon in the rocks.
Finding a potpourri of life of this age suggests that marine ecosystems rebounded quickly after the Great Dying, within just 1 million years or so, Dai says.
Alternatively, it may indicate that the extinction event failed to wipe out entire trophic levels, says paleontologist William Foster from the University of Hamburg in Germany, who was not involved in the study. “You have this really environmentally stressful world, but some former marine ecosystems survive.”
Regardless, it seems clear that these ecosystems were hardy. Due to the motion of tectonic plates, the community preserved in the Guiyang biota was located in the tropics during the early Triassic. At that time, the temperature of the sea surface was nearly 35⁰ Celsius, and past research had suggested many organisms may have migrated away to escape the heat. But, the discovery of the Guiyang biota challenges that, Foster says. Sea creatures “are tolerating it somehow, they’re adapting.”
According to Dai, the fossils may be evidence that the roots of today’s marine ecosystems took hold shortly after the Great Dying. “These groups are related to modern fish, lobsters and shrimps, their ancestors,” he says. “The oldest time we can find similar seafood to today is [in the time of] the Guiyang biota.”
But Roopnarine is skeptical. It remains to be seen exactly how the Guiyang biota connects to today’s ecosystems, he says. The fossil assemblage could represent an ephemeral collective of life rather than a stable community, he adds, pointing out that ammonoids and conodonts went extinct.
Further work will help resolve the many questions unearthed with the Guiyang biota, Dai says. He and his colleagues plan to head back into the field this summer for the first time since 2019. When asked if he’ll be keeping his eyes peeled for another lobster, he responds: “Of course.” More
Making molecules faster: Discovery dramatically reduces time it takes to build molecules
With a big assist from artificial intelligence and a heavy dose of human touch, Tim Cernak’s lab at the University of Michigan made a discovery that dramatically speeds up the time-consuming chemical process of building molecules that will be tomorrow’s medicines, agrichemicals or materials.
The discovery, published in the Feb. 3 issue of Science, is the culmination of years of chemical synthesis and data science research by the Cernak Lab in the College of Pharmacy and Department of Chemistry.
The goal of the research was to identify key reactions in the synthesis of a molecule, ultimately reducing the process to as few steps as possible. In the end, Cernak and his team achieved the synthesis of a complex alkaloid found in nature in just three steps. Previous syntheses took between seven and 26 steps.
“Making a chemical structure that has atoms in just the right place to give you efficacious and nontoxic medicines, for instance, is tricky,” said Cernak, assistant professor of medicinal chemistry and chemistry. “It requires a chemical synthesis strategy grounded in the chemical building blocks you can actually buy and then stitch together using chemical reactions.”
The accomplishment has powerful implications for speeding up the development of medicines.
Cernak compared the construction of these complex molecules to playing chess. You need to orchestrate a series of moves to get to the end of the game. While there’s a near infinite number of possible moves, there’s a logic that can be followed.
“We developed a logic here, based in graph theory, to get to the end as quickly as possible,” he said.
Cernak and colleagues used SYNTHIA Retrosynthesis Software, which provides scientists with a database of pathways, or steps, and formulas for millions of molecular structures. This gave the team an enormous amount of computational synthesis data to play with.
Using an algorithm they developed to curate the data, the researchers identified the steps along the pathway that were high impact, or key steps, and the steps that were making progress toward completing the synthesis but ultimately inefficient for the whole process.
“We hope this research can lead to better medicines,” Cernak said. “So far, we have been limited in the molecular structures we can quickly access with chemical synthesis.”
Co-authors include Yingfu Lin, senior research fellow in pharmacy; Rui (Sam) Zhang, doctoral student in chemistry; and Di Wang, doctoral student in pharmacy. More
