The earliest of the Big Five, the end-Ordovician or Ordovician-Silurian extinction events some 444 million years ago, are reckoned by many to be the second largest.

五次大灭绝中发生最早的一次是奥陶纪末期或者奥陶纪-志留纪大灭绝事件，发生在大约4亿4千4百万年前。许多科学家估计这次规模是五次当中第二大的。