A series of severe environmental crises in the oceans, spanning 185 to 85 million years ago, significantly altered the course of evolution on Earth. This "tag-team" between the oceans and continents had devastating consequences for marine life and left a lasting impact on our planet's biological history.
Oceanic Anoxic Events: The Trigger for Mass Extinctions
According to Interesting Engineering, researchers have identified these environmental crises as "oceanic anoxic events," periods when dissolved oxygen levels in the oceans plummeted to critically low levels. This depletion of oxygen led to major biological upheavals, including mass extinctions of marine species.
The study, spearheaded by the University of Southampton, involved collaboration with universities from across the globe, including Leeds, Bristol, Adelaide, Utrecht, Waterloo, and Yale.
"Oceanic anoxic events were like hitting the reset button on the planet's ecosystems. The challenge was understanding which geological forces hit the button," said the study's lead author, Tom Gernon, who also works as Southampton's Earth Science Professor.
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Impact of Tectonic Forces on Ocean Chemistry
The research focused on the Mesozoic era, which encompasses the Jurassic and Cretaceous periods, a time commonly known as the age of the dinosaurs.
Evidence from this era can be observed along the Jurassic Coast in the UK, as well as in the cliffs of Whitby and Eastbourne. By combining statistical analysis and computer models, the scientists sought to understand how chemical cycles in the oceans responded to the breakup of the supercontinent Gondwana.
Gondwana, once a massive landmass where dinosaurs roamed, began to break apart during the Mesozoic era, triggering intense volcanic activity worldwide. This volcanic activity, the researchers suggest, played a crucial role in shaping the Earth's evolutionary path.
The Role of Phosphorus in Marine Ecosystems
As tectonic plates shifted and new seafloors formed, large amounts of phosphorus, a nutrient essential for life, were released into the oceans through the weathering of volcanic rocks.
According to the researchers, these pulses of chemical weathering disrupted the oceans, creating a "geological tag-team" effect. The timing of these weathering events closely matched the occurrence of most oceanic anoxic events recorded in geological history.
Phosphorus acts as a natural fertilizer, stimulating the growth of marine organisms. However, this surge in biological activity led to the sinking of large amounts of organic matter to the ocean floor, which in turn consumed vast quantities of oxygen.
As a result, vast areas of the oceans became anoxic, or oxygen-depleted, creating "dead zones" where most marine life perished. These anoxic events typically lasted one to two million years and had lasting impacts on marine ecosystems, effects that are still felt today.
A Legacy of Mass Extinction and Resource Formation
The rocks formed during these anoxic events, rich in organic matter, have become the primary source of today's commercial oil and gas reserves.
According to Benjamin Mills, Professor of Earth System Evolution at the University of Leeds, the study highlights the profound impact of nutrient overloading on ocean ecosystems, a cautionary tale for the modern world. Human activities have already reduced global oceanic oxygen levels by about two percent, significantly expanding anoxic water masses.
Understanding Earth's Interior and Surface Connections
The findings of this study reveal a strong connection between Earth's solid interior and its surface environment, especially during periods of tectonic and climatic upheaval.
Gernon emphasizes the remarkable chain of events that can occur within Earth, often with devastating effects on the surface. The breakup of continents, for example, can have profound repercussions for the course of evolution, highlighting the fragile balance that governs life on Earth.
To view this peer-reviewed study, click here.
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