Scientists believe that the dinosaurs were killed when an asteroid hit the Earth, but according to a new study, the massive impact may have also wiped out the ancient mollusk.
Researchers from the University of Southampton and the Leibniz Center for Tropical Marine Ecology looked into the potential role the Chicxulub impact played in the acidification of oceans during the end of the Cretaceous period 66 million years ago.
They discovered that the species of ancient mollusks called ammonites became extinct around the same time as the great Chicxulub impact occurred. The event also marked the extinction of 90 percent of plankton with calcium carbonate shells (foraminifera and coccolithophores).
Other groups in the ocean that did not have calcium carbonate shells were not as severely affected by the impact as those that had this type of shell.
The researchers believe this raises the possibility that an acidification of the oceans occurred as a consequence of the impact, causing only a select group of organisms to become extinct.
While the ammonites and other planktonic calcifiers were able to adapt to the gradual increase of carbon dioxide (CO2) content in the ocean waters before, the impact of the asteroid significantly changed the ocean acidification.
The researchers recreated several acidifying factors, such as wildfires, that occurred following the asteroid's impact in their first modeling study. The resulting CO2 emissions dissolved in seawater and lowered the pH level of the ocean. This made the water more acidic and corrosive, especially to calcium carbonate shells.
Gypsum rocks were also vaporized, leading to the formation of sulfuric acid rain that mixed with the waters of the ocean.
According to their findings, the researchers concluded that the levels of ocean acidification after the Chicxulub impact were not enough to have caused the extinction of the ammonites and other planktonic calcifiers.
"While the consequences of the various impact mechanisms could have made the surface ocean more acidic, our results do not point to enough ocean acidification to cause global extinctions," said Ocean and Earth Science Professor Toby Tyrrell from the University of Southampton.
"Out of several factors we considered in our model simulation, only one (sulfuric acid) could have made the surface ocean severely corrosive to calcite, but even then the amounts of sulfur required are unfeasibly large."
Tyrrell suggested that other possible causes of the extinction, such as the prolonged darkness created by the aerosols and soot that were launched into the Earth's atmosphere, should be investigated.
The study is published in the journal Proceedings of the National Academy of Sciences.
Photo: Gorissen M | Flickr
