Tiny worms sparked explosive evolutionary period of life on Earth

If you were asked to name the heroes of Earth’s evolution, chances are worms wouldn’t top the list. Yet, new research suggests these humble burrowers played a pivotal role in one of the most significant periods of biodiversity growth on our planet.

Great Ordovician Biodiversification Event

Approximately 480 million years ago, a pivotal event in Earth’s history took place, known as the Great Ordovician Biodiversification Event (GOBE). 

This event spanned a considerable duration of roughly 30 million years and marked a period of extraordinary diversification in the planet’s biosphere, especially with marine life. 

The number of marine genera increased dramatically, particularly among invertebrates such as brachiopods, trilobites, bryozoans, and mollusks.

This diversification occurred across various marine habitats, from shallow shelf areas to deep ocean environments.

Several factors likely contributed to the GOBE. The breakup of the supercontinent Gondwana increased the length of coastlines and created new habitats for marine life to colonize.

Additionally, a rise in sea levels during the Ordovician expanded the area of shallow continental shelves, providing more space for biodiversity to flourish.

Changes in ocean chemistry, such as increased oxygenation and nutrient availability, may have also played a role in supporting the proliferation of life.

Prehistoric worms in evolution

Researchers at Johns Hopkins University unveiled a remarkable discovery that challenges traditional understanding of the GOBE. 

Their findings suggest that the seemingly insignificant burrowing behaviors of prehistoric worms and other invertebrates in the ocean floor may have been the driving force behind this significant evolutionary explosion.

This revelation highlights the potential for overlooked ecological interactions to play a pivotal role in shaping life’s trajectory.

Oxygen, minerals and worms

The key to this discovery lies in the relationship between sediment mixing, a mineral called pyrite, and oxygen levels.

As worms burrowed, they mixed up sediments, unearthing pyrite. This mineral, in turn, reacted with oxygen in the water, increasing oxygen levels in both the ocean and the atmosphere.

“It’s really incredible to think how such small animals, ones that don’t even exist today, could alter the course of evolutionary history in such a profound way,” remarked Maya Gomes, an assistant professor in the Department of Earth and Planetary Sciences at Johns Hopkins University.

Goldilocks zone

The research team, led by Gomes, measured pyrite levels from nine sites along the Chesapeake Bay, a modern-day proxy for early ocean conditions.

They found that sites with a moderate amount of sediment mixing held the highest levels of pyrite. This finding challenges the long-held belief that sediment mixing would decrease oxygen levels by exposing pyrite to oxygen in the water.

“It’s kind of like Goldilocks. The conditions have to be just right. You have to have a little bit of mixing to bring the oxygen into the sediment, but not so much that the oxygen destroys all the pyrite and there’s no net buildup,” explains Kalev Hantsoo, the study’s first author.

Worm-driven oxygen boost in evolution

By incorporating their recent findings into pre-existing models that monitor oxygen levels over geological time, the researchers identified a significant increase in oxygen concentration during the Ordovician period, which coincided with the occurrence of the GOBE. 

This observed correlation strongly suggests that the elevated oxygen levels, facilitated by the burrowing activities of worms and other invertebrates, may have played a crucial role in triggering and sustaining the remarkable surge in biodiversity that characterized this period. 

The increased availability of oxygen by worms could have provided the necessary conditions for the evolution and proliferation of diverse life forms, leading to the significant expansion and diversification of species observed during the GOBE.

Rethinking history

This remarkable research sheds new light on the role of oxygen and worms in shaping Earth’s evolutionary history.

“There’s always been this question of how oxygen levels relate to the moments in history where evolutionary forces are ramped up and you see a greater diversity of life on the planet,” said Gomes.

While oxygen levels likely played a critical role in the GOBE, other factors may have driven earlier evolutionary events like the Cambrian explosion.

“The new models allow us to rule out oxygen and focus on other things that may have driven evolution during that time,” says Gomes.

This study not only reveals a fascinating chapter in Earth’s history, but it also underscores the importance of understanding the complex interplay of factors that shape our planet’s evolution.

The study is published in the esteemed journal Geochimica et Cosmochimica Acta.

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