The Manicouagan Crater in the Canadian province of Quebec is the largest plainly visible impact crater on Earth, and the sixth largest overall. Roughly 100 kilometers in diameter -- a little more than half the size of the Chicxulub Crater in Mexico (the crater associated with the extinction of the dinosaurs) -- it forms a tidy ring of water encircling a large island. The asteroid that made Manicouagan was once considered as a possible trigger for the Triassic–Jurassic extinction event, which set the stage for dinosaurs to dominate Earth. Mineral dating, however, shows that the crater was carved more than 12 million years before the mass extinction, so it couldn't have been the cause.

The Manicouagan impact was far from harmless, however. A new study published to Scientific Reports suggests that it prompted a large extinction event of its own, and may have contributed to the eventual Triassic–Jurassic extinction around 200 million years ago.

Japanese researchers extensively surveyed a claystone layer that accumulated in a deep seafloor environment in an equatorial region of the Panthalassa Ocean (location marked by the red area in the figure above). The Panthalassa Ocean was the vast body of water that surrounded the supercontinent Pangaea. They found that, around 214 to 215 million years ago, approximately the same time of the Manicouagan impact, a great many species of plankton called Radiolarians abruptly disappeared, while tons of new species sprung up. Moreover, the massive turnover in life forms coincided with an anomalous increase in platinum group elements, which the researchers believe originated from an extraterrestrial source. This source -- probably an asteroid -- was between 3.3 and 7.8 kilometers in diameter and slammed the Earth at a speed of around 20 kilometers/second, they estimate. (Figure below: Note that rates of extinction and origination (new species) abruptly increased 214 million years ago.)

The disruption in the ocean food chain almost certainly impacted other species. Shelled, swimming Ammonites, similar in appearance to modern-day nautiluses, experienced significant declines in diversity in the years leading up to the Triassic-Jurassic extinction, while eel-like Conodonts went extinct altogether.

The asteroid impact combined with other catastrophes like volcanic eruptions and sudden depletions of ocean oxygen to drastically thin the number of species on Earth at the end of the Triassic. When the Jurassic period began roughly 201 million years ago, at least half of all known species had vanished.

Source: Onoue, T. et al. Bolide impact triggered the Late Triassic extinction event in equatorial Panthalassa. Sci. Rep. 6, 29609; doi: 10.1038/srep29609 (2016).

(Image: NASA)