Asteroid wiped out dinosaurs, acidified the sea 66 million years ago

The impact of the meteorite with Earth 66 million years ago not only caused the extinction of the dinosaurs, but also turned the oceans into acid, killing a variety of marine life.

When the 10km wide asteroid crashed to Earth 66 million years ago (an event known as Chicxulub), the dinosaurs were wiped out.

However, the exact fate of Earth’s then-diversified ocean dwellers – the stalagmites, giant sea lizards and other marine life – remains poorly understood.

New research now shows that the event that ended the dinosaur dynasty also acidified the planet’s oceans, disrupting the food chain that sustains aquatic life and leading to mass extinctions.

The study, published October 21 in the Proceedings of the National Academy of Sciences, theorized that the destructive impact of marine life during the Chicxulub event – the result of sulfur-rich rocks pouring acid rain into the ocean – as serious as the fire and fury it brought to land.

“It’s acidification instantaneously, it transforms the ecosystem for millions of years. We were shocked to find this,” said Noah Planavsky, a biologist at Yale University and one of the authors of the study. research, told the New York Times.

Asteroid wiped out dinosaurs, acidified the sea 66 million years ago
An illustration of the Chicxulub crater formed shortly after the meteorite hit the Earth. (Photo: Science Source).

The impact of the asteroid Chicxulub – named after the crater it formed around the Gulf of Mexico – sent columns of rock into Earth’s atmosphere, incinerating the planet’s forests and sending tsunami waves across the continents. ocean. But the link between the incident and the marine extinction proved less solid.

That gap haunted geographer Michael Henehan’s mind when he attended a conference in 2016 in the Netherlands that included an exploration of the cave system at Geulhemmerberg, which contains rocks from the late Cretaceous.

There he encountered a surprisingly thick layer of rock made of gray clay that formed shortly after the meteorite hit and has collected several rock samples.

Back in the lab at Yale University, Dr. Henehan, now a researcher at the GFZ Helmholtz Center in Potsdam, Germany, cleaned the rocks and found the fossilized shells of thousands of marine plankton. small species called foraminifera, or forams.

Asteroid wiped out dinosaurs, acidified the sea 66 million years ago
Foram shells, shown at 8x magnification, were collected in the Geulhemmerberg caves in the Netherlands. They provide clues to ocean acidity levels after the asteroid hit. (Photo: Michael J. Henehan).

He explained that the discovery of so many seashells is lucky because they preserve small amounts of boron, the chemical element scattered in such fossils, which in turn provides clues to the ocean’s ancient acidity levels. .

Dr. Henehan and his team measured boron and found that the relative ratios of the two elemental isotopes changed dramatically at the time of the impact.

Dr Planavsky explains that in shells like these, the ratio of boron isotopes changes as the acidity of the oceans increases. Since this ancient change happened in the first 100 to 1,000 years after the impact, it means that the oceans became acidic overnight.

The immediate acidification would wreak havoc on the organisms that form the foundation of the ecosystem, leading to problems for other organisms such as ammonites that live higher up the food chain.

This study provides evidence of what sustained the sea extinction after the asteroid impact turned things upside down. It confirmed that the asteroid triggered the extinction in the first place.

Asteroid wiped out dinosaurs, acidified the sea 66 million years ago
Sedimentary layers in the Geulhemmerberg cave, marking the transition from the Cretaceous to the Paleozoic. (Photo: Michael J. Henehan).

Around the time that the asteroids hit, intense volcanic activity caused more than 200,000 miles of lava to erupt over the course of about a million years.

For a long time, it was not clear whether the mass extinction at sea stemmed from changes caused by volcanoes or by asteroids. But since the boron shift occurs exactly at the boundary, it is clear that the asteroid has a larger impact.

“It’s very strong evidence that ocean acidification is caused by meteorites, not volcanoes,” Dr Lowery said.

Whatever the ancient events, immediate acidification and mass extinction are relevant to our modern world. According to a report from the United Nations Intergovernmental Panel on Climate Change, human emissions of carbon dioxide not only warm the planet but also acidify the oceans.

That modern acidification is happening at a rate and scale comparable to asteroid-triggered acidification, according to Dr. Planavsky. He thinks we could suffer the same consequences in the next 100 years.