The six-mile-long (10 km) asteroid that killed the non-avian dinosaurs may have also triggered a global lethal algal bloom, killing a lot of marine animals, a new study suggests.
About 66 million years ago, the asteroid hit Earth in the Yucatan Peninsula and created the Chicxulub crater – which is 12 miles (20 kilometres) deep and 110 miles (180 kilometres) across – according to the American Geophysical Union (AGU). Of all the animal species at that time, 75 percent of them went extinct.
The American Geophysical Union said that scientists were unsure why so many marine animals – such as the ammonites and the plesiosaurs – also died, since the water should have protected them form the thermal radiation caused by the asteroid impact.
In the new study – published November 4 in the Journal of Geophysical Research: Planets – the researchers looked at how fragments of vaporized and molten rock would have acted when thrown out of the Earth’s atmosphere, only to fall back on the planet. According to the American Geophysical Union report, as the fireballs re-entered the atmosphere they generated large amounts of nitrogen oxide gasses.
It is possible that the nitrogen oxide gasses triggered acid rain, which increased the levels of nitrate in the oceans. This would have caused an algal bloom across the globe. Researchers said that the algal bloom would have led to increased harmful toxins that disturbed the marine ecosystem, killing off countless marine species.
Devon Parkos, lead author of the study and an aerospace engineer at the School of Aeronautics and Astronautics at Purdue University in Indiana, said that almost any creature that was alive at that time was affected by the Chicxulub impact.
To better understand how the hot rock fragments affected marine life, the researchers used models made for spaceship re-entry. They analysed how low-pressure conditions and high-altitude would have affected the fragments.
The findings show that those unusual conditions led to the production of high levels of nitrogen oxide.
Researchers said that, over time, the algal bloom would have exhausted the supply of phosphates and nitrated in the water, causing a shortcoming in the marine nutrient cycles. The bloom would have also reduced the levels of dissolved oxygen in the water, and it would have blocked the sunlight needed by the phytoplankton to survive.
Those types of algae could have also created lethal toxin that harm shellfish, according to the American Geophysical Union. Parkos said that, based on the fossil record, the shellfish population did not prosper at all after the asteroid impact.
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