Nature World: Acid rain and ozone depletion may have caused the Earth's most severe known mass extinction, a new study published in the journal Geology suggests.
Some 250 million years ago, at the end of the Permian period, more than 90 percent of marine species and over 70 percent of terrestrial species died off, setting the scene for the day of the dinosaur.
The die-off was so extreme that, according to fossil records left behind, ecological diversity was not fully restored for another several million...