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Earth's evolution was shaped by a series of major environmental crises that occurred millions of years ago, profoundly affecting both marine and terrestrial ecosystems. These events triggered mass extinctions, disrupted chemical cycles, and paved the way for new forms of life to emerge.
Evolution of the Earth and catastrophes
A catastrophic "tag team" between continents and oceans wiped out marine life, depleted oxygen levels and dramatically changed the course of evolution on our planet, a new study has found. These events left a lasting mark on Earth's biodiversity. The study was led by a group of scientists from the University of Southampton. The findings provide new explanations for oceanic anoxic events—periods when the seas were critically depleted of dissolved oxygen—that occurred between 185 and 85 million years ago.
Depletion of oxygen in the ocean in the Mesozoic era
The study focused on several significant oceanic anoxic events spanning 185 to 85 million years ago, during the Mesozoic Era. The study's lead author, Professor Tom Gernon of the University of Southampton, called these events 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 what geological forces pushed the button,” Professor Gernon said.
Breakup of Gondwana
Using complex statistical analysis and advanced computer modeling, the team explored how the breakup of Gondwana, the supercontinent once inhabited by dinosaurs, could have affected chemical cycles in the ocean. all over the world," noted Professor Gernon.
As the tectonic plates shifted and a new sea floor formed, large amounts of phosphorus were released into the oceans from volcanic rocks, which acted as a natural fertilizer that supported the development of marine life.
"We show that enhanced weathering of mafic lithologies during continental breakup and the initiation of seafloor spreading can likely trigger a sequence 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 implications of these fertilization episodes.
"Increased biological activity caused huge amounts of organic matter to sink to the bottom of the ocean, where it consumed large amounts of oxygen," Professor Mills said. This process created marine dead zones where most marine life died.
“These anoxic events typically lasted between one and two million years and had profound effects on marine ecosystems. The organic-rich rocks that accumulated during these events are by far the largest source of commercial oil and gas reserves worldwide,” Mills concluded.
The researchers highlighted that today's human activities, such as pollution, deforestation and the excessive use of fertilizers in agriculture, are lowering the average oxygen level in the ocean by about two percent. The decrease is accelerating the expansion of oxygen-free water masses, creating larger dead zones in the oceans where marine life fighting for survival. This further threatens global biodiversity and the stability of marine ecosystems.
"The study of geological events provides valuable information that can help us understand how the Earth may respond to future climate and environmental stresses," Professor Gernon said.
Connection of the inner part of the Earth with its external appearance
The study highlights the often underestimated connection between Earth's interior and the surface, showing 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 pathways over millions of years.
"It's amazing how a chain of events on Earth can affect the surface, often with devastating consequences. The tearing apart of continents could have serious consequences for evolution," said Professor Gernon.
Lessons of Earth's evolution
The study not only illuminates key moments in Earth's evolution, but also offers valuable insights into current environmental issues. By analyzing the geological and biological processes that caused ancient mass extinctions, researchers can draw parallels with today's climate problems. This understanding could be important in developing strategies to deal with the ongoing effects of climate change and the degradation of marine ecosystems. The study is published in the journal Nature Geoscience.
