Gondwana, land of dinosaurs, tore apart causing mass extinction in the seas

Something catastrophic happened 100 million years ago that changed the way our planet evolved. Scientists say that several intense environmental events followed each other leading to the widespread extinctions of marine species.

Between 185 and 85 million years ago, a series of severe environmental crises, called oceanic anoxic events, took place. There hasn't been a viable explanation for it, until now. A study has thrown light on what caused these crises that critically depleted dissolved oxygen in the seas.

Experts from the University of Southampton said certain events triggered severe biological changes on Earth, including mass extinctions of marine species. The findings were recently published in the journal Nature Geoscience.

Lead author Tom Gernon, a Professor of Earth Science at Southampton, said, “Oceanic anoxic events were like hitting the reset button on the planet’s ecosystems. The challenge was understanding which geological forces hit the button.”

Scientists studied the impact of plate tectonic forces on ocean chemistry during the age of the dinosaurs, that is during the Jurassic and Cretaceous Periods. These periods combined are known as the Mesozoic era.

The researchers studied how the breaking up of the supercontinent Gondwana could have affected chemical cycles in the ocean. Notably, Gondwana was the great landmass which comprisedaround two-thirds of today's continental area. This is the land where once dinosaurs walked the Earth.

Professor Gernon said, “The Mesozoic era witnessed the breakup of this landmass, in turn bringing intense volcanic activity worldwide. As tectonic plates shifted and new seafloors formed, large amounts of phosphorus, a nutrient essential for life, were released from weathering volcanic rocks into the oceans."

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"Crucially, we found evidence of multiple pulses of chemical weathering on both the seafloor and continents, which alternately disrupted the oceans.”

“It’s like a geological tag team,” said Prof Gernon.

What killed marine life?

The study authors noticed that the timing of these pulses matched the most oceanic anoxic events in the rock record.

The influx of phosphorus to the ocean boosted the growth of marines but came at a major cost for marine ecosystems. Huge amounts of organic matter sank to the ocean floor and consumed large quantities of oxygen, co-author Benjamin Mills, a Professor of Earth System Evolution at the University of Leeds, said.

He added, “This process eventually caused swathes of the oceans to become anoxic, or oxygen-depleted, creating ‘dead zones’ where most marine life perished."

The events lasted around one to two million years and impacted marine ecosystems immensely and the effects continue to reverberate even today.