The activities of prehistoric worms boring holes in the ocean floor released oxygen, contributing to the Great Ordovician Biodiversity Event, according to a new study. One of Earth’s greatest biodiversity explosions—a 30-million-year period of explosive evolutionary change that gave rise to countless new species—may owe a vital turning point in the history of life to even the humblest of creatures: worms.

The burrowing and burrowing of prehistoric worms and other invertebrates on the ocean floor triggered a chain of events that released oxygen into the ocean and atmosphere and helped kick off what became known as the Great Ordovician Biodiversity Event about 480 million years ago, according to New Johns Hopkins. University researchers published in the journal Geochimica and Cosmochimica Acta.

“It is truly incredible to imagine how such tiny animals that do not even exist today could so profoundly change the course of evolutionary history,” said senior author Maya Gomez, an assistant professor in the Department of Earth and Planetary Sciences. “With this work, we will be able to study the chemistry of the early oceans and rethink parts of the geological record.”

To better understand how changes in oxygen levels affect large-scale evolutionary events, Gomez and his research team updated models that detail the timing and rate of oxygen increases over hundreds of millions of years.

Sediment mix and oxygen levels

In particular, they investigated the relationship between the mixing of sediment caused by burrowing worms and a mineral called pyrite, which plays an important role in storing oxygen. The more pyrite forms and is buried under silt, silt or sand, the greater the oxygen levels.

The researchers measured pyrite at nine locations along the Chesapeake Bay coastline in Maryland that are representative of early ocean conditions. Areas with rainfall mixing of even a few centimeters contained significantly more pyrite than areas with no mixing and deep mixing.

The findings challenge previous assumptions that the relationship between pyrite and precipitation mixing remains constant across habitats and over time, Gomez said.

According to traditional belief, as animals dug into the ocean floor, churning up sediments, the newly found pyrite was exposed to oxygen in the water and destroyed; This process eventually prevented oxygen from accumulating in the atmosphere and ocean. Mixed sediments were seen as evidence that oxygen levels were stable.

New evidence suggests that small amounts of sediment mixed into water with very low oxygen levels will expose buried pyrite, sulfur and organic carbon to enough oxygen to initiate the formation of more pyrite.

“It’s like Goldilocks. The conditions have to be perfect. You have to stir a little bit to get oxygen into the sediment, but not so much that the oxygen destroys all the pyrite and there’s no clear accumulation,” said Kalev Hantsu, a postdoctoral researcher at Johns Hopkins and first author of the study. article.

Oxygen levels and evolutionary events

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

The extra oxygen likely fueled the Great Ordovician Biodiversity Event, during which new species evolved rapidly, the researchers said.

“There’s always been a question about how oxygen levels relate to times in history when evolutionary forces accelerated and you saw a greater diversity of life on the planet,” Gomez said. said. “There was also a large-scale speciation event during the Cambrian period, but the new models allow us to exclude oxygen and focus on other things that may have driven evolution during that period.”