Modeling had previously produced evidence of this ecological collapse but the mechanisms through which it occurred were unknown. To overcome this, the team of researchers led by Michael Henehan, a postdoctoral scientist at the GFZ Research Center in Potsdam, studied sea shells trapped in sediment that formed just after the asteroid hit.
The samples were taken from caves and rivers in the Netherlands, Mississippi and Texas, as well as from deep-sea drilling sites, according to the paper.
They found that the shell walls had become very thin due to a sharp drop in the pH of the oceans – a sign of acidification – 100 to 1,000 years after the strike. This demonstrated that asteroid impact was the main culprit for making the oceans more acidic and causing a mass die-off of marine life, the researchers said. Intense volcanic activity had also been considered a possible cause.
So far, ocean pH has dropped from 8.2 to 8.1 since the industrial revolution, and is expected to drop by another 0.3 to 0.4 pH units by the end of the century, it added. Henehan's research showed a 0.25 pH unit drop 66 million years ago.