Earth’s evolution has been shaped by a series of major environmental crises that occurred millions of years ago and profoundly affected both marine and terrestrial ecosystems. These events triggered mass extinctions, disrupted chemical cycles, and paved the way for the emergence of new life forms.

The evolution of the world and disasters

A new study has revealed that a catastrophic “tag team” between continents and oceans wiped out marine life, depleted oxygen levels and dramatically altered the course of evolution on our planet. These events left a lasting mark on Earth’s biodiversity. The study was led by a team of scientists from the University of Southampton. The findings provide new explanations for oceanic anoxic events – periods when dissolved oxygen in the seas was critically depleted – that occurred between 185 and 85 million years ago.

Depletion of ocean oxygen during the Mesozoic era

The study focused on several major ocean anoxic events during the Mesozoic Era, spanning between 185 and 85 million years ago. Lead author of the study, Professor Tom Gernon from the University of Southampton, described these events as a “reset button” for the planet.

“Anoxic events in the ocean were like pressing a reset button for the planet’s ecosystems. The challenge was to understand which geological forces were pressing the button,” said Professor Gernon.

Breakup of Gondwana

“Using sophisticated statistical analyses and advanced computer modelling, the team investigated how the break-up of Gondwana, the supercontinent where dinosaurs once lived, could have affected chemical cycles in the ocean across the world,” said Professor Gernon.

As tectonic plates shifted and new seafloor formed, large amounts of phosphorus were released into the oceans from volcanic rocks, acting as a natural fertilizer that supported the growth of marine life.

“We show that increased erosion of mafic lithologies and the onset of seafloor spreading during continental breakup could likely trigger a series of anoxic events,” the researchers write.

Significant impact on marine ecosystems

Professor Benjamin Mills, an expert on the evolution of the Earth system at the University of Leeds, has detailed the consequences of these fertilisation events.

“The increased biological activity caused large amounts of organic matter to sink to the bottom of the ocean, where large amounts of oxygen were consumed,” Professor Mills said. This process created dead zones in the sea where most marine life died.

“These anoxic events typically lasted one to two million years and had profound effects on marine ecosystems. The organic-rich rocks deposited during these events are by far the largest source of commercial oil and gas reserves worldwide,” Mills concluded.

The researchers highlighted that modern-day human activities, such as pollution, deforestation and excessive use of fertilizers in agriculture, have reduced the average oxygen level in the oceans by about two percent, accelerating the expansion of oxygen-depleted water masses, larger dead zones in the oceans where marine life struggles to survive. This further threatens global biodiversity and the stability of marine ecosystems.

“Studying geological events provides valuable information that can help us understand how the Earth might respond to future climate and environmental stresses,” Professor Gernon said.

The connection between the Earth’s interior and the exterior

The study highlights the often-underestimated connection between the Earth’s interior and surface, and shows how tectonic activity deep within the planet can dramatically affect the state of the surface. These interactions drive processes such as volcanic eruptions, nutrient cycles, and changes in ocean chemistry that play a critical role in shaping ecosystems and evolutionary paths over millions of years.

“It is amazing how a chain of events can affect the surface of the Earth, often with catastrophic consequences. The breakup of continents can have serious consequences for evolution,” said Professor Gernon.

Lessons from the evolution of the world

The study not only illuminates key moments in Earth’s evolution, but also provides valuable insight into current environmental issues. By analyzing the geological and biological processes that led to ancient mass extinctions, researchers can draw parallels to today’s climate challenges. This understanding could be important in developing strategies to cope with the ongoing effects of climate change and the degradation of marine ecosystems. The study was published in the journal Nature Geology.