One of the planet’s most dramatic extinctions was caused in part by ocean acidification, which has become a problem in our own era.
The worst day in the history of life on Earth, so far, happened almost exactly 66 million years ago, when an asteroid roughly the size of Manhattan slammed into the Yucatán Peninsula.
You may know the story. The asteroid—which arrived, probably, in June or July—immediately drilled a 20-mile hole into the planet’s surface, vaporizing bedrock and ejecting it halfway to the moon. The planet shuddered with magnitude-12 earthquakes, loosing tsunamis across the Gulf of Mexico. Some of the ejected debris condensed in orbit and plunged back to Earth as searing spheres of molten glass, which torched the land and turned forests into firestorms. Other debris remained high in space, where it blocked the sun’s rays and began to chill the surface of the planet.