Asteroid impact acidified the prehistoric ocean

Abstract

Sixty-six million years ago, an asteroid struck the earth, initiating mass species die-offs. Scientists have long believed that the impact’s marine extinctions were due to ocean acidification, but they never had physical evidence for that hypothesis—until now. A new study uses boron isotopes in tiny plankton shells to reconstruct the pH of the oceans around the time of the impact, providing evidence for a rapid acidification event that disrupted the marine ecosystem for hundreds of thousands of years (Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1905989116). Within 1,000 years of the impact, the pH of the surface oceans dropped by 0.25 units, the new work shows. The researchers also investigated the ecological impact of the asteroid and found that the amount of photosynthesis by aquatic organisms was cut in half during the same time frame. Although the pH of the oceans returned to preimpact levels within about 40,000 years, the