How worms fueled Earth’s biodiversity explosion

One of the most consequential bursts of biodiversity on Earth—a thirty-million-year period of explosive evolutionary change that spawned countless new species—may owe its humblest of creatures to this crucial stage in the history of life: worms.

The burrowing and burrowing of prehistoric worms and other invertebrates along the ocean floors set off a series of events that released oxygen into the ocean and atmosphere and helped trigger what is known as the Great Ordovician Biodiversification Event, about 480 million years ago, according to new sources. findings Researchers from Johns Hopkins University published in the journal Geochimica and Cosmochimica Acta.

“It’s truly incredible to think how such small animals, which don’t even exist today, could change the course of evolutionary history in such a profound way,” said senior author Maya Gomes, assistant professor in the Department of Earth and Planetary. Sciences. “This work will allow us to explore the chemistry of early oceans and reinterpret parts of the geological record.”

To better understand how changes in oxygen levels affected large-scale evolutionary events, Gomes and her research team updated models that detail the timing and rate of increasing oxygen over hundreds of millions of years.

They examined the relationship between sediment mixing, caused in part by worms’ burrowing, with a mineral called pyrite, which plays a key role in building oxygen. The more pyrite forms and becomes buried under the mud, silt or sand, the more oxygen levels rise.

Researchers measured pyrite at nine locations along the coastline of Maryland’s Chesapeake Bay, which serves as a benchmark for early ocean conditions. Sites with even a few centimeters of sediment mixing contain significantly more pyrite than sites with no mixing and sites with deep mixing.

The findings challenge previous assumptions that the relationship between pyrite and sediment mixing remained the same across habitats and through time, Gomes said.

Conventional wisdom held that as animals churned up sediments by burrowing into the ocean floor, newly excavated pyrite would have been exposed to and destroyed by oxygen in the water, a process that would ultimately prevent oxygen from accumulating in the atmosphere and ocean. Mixed sediments were seen as evidence that oxygen levels remained stable.

The new data suggests that a small amount of sediment mixing with water with very low oxygen levels would have exposed buried pyrite, sulfur and organic carbon to just enough oxygen to trigger the formation of more pyrite.

“It’s a bit like Goldilocks. The conditions have to be just right. You have to mix a little to introduce the oxygen into the sediment, but not so much that the oxygen destroys all the pyrite and there is no net build-up,” said Kalev Hantsoo , a doctoral candidate at Johns Hopkins and first author of the paper.

When the researchers applied this new relationship between pyrite and the depth of sediment mixing to existing models, they found that oxygen levels remained relatively flat for millions of years and then rose during the Paleozoic, with a steep rise during the Ordovician period.

The extra oxygen likely contributed to the Great Ordovician Biodiversification Event, when new species rapidly flourished, the researchers said.

“There has always been the question of how oxygen levels relate to the moments in history when evolutionary forces are ramped up and you see greater diversity of life on the planet,” Gomes said. “The Cambrian period also had a massive speciation event, but the new models allow us to rule out oxygen and focus on other things that may have driven evolution during that time.”