Extinctions
The first of five great mass extinctions was the Ordovician-Silurian extinction . Its possible cause was the intense glaciation of Gondwana, which eventually led to a snowball earth . 60% of marine invertebrates became extinct and 25% of all families. The second mass extinction was the Late Devonian extinction , probably caused by the evolution of trees, which could have led to the depletion of greenhouse gases (like CO2) or the eutrophication of water. 70% of all species became extinct. The third mass extinction was the Permian-Triassic, or the Great Dying , event was possibly caused by some combination of the Siberian Traps volcanic event, an asteroid impact, methane hydrate gasification, sea level fluctuations, and a major anoxic event . Either the proposed Wilkes Land crater in Antarctica or Bedout structure off the northwest coast of Australia may indicate an impact connection with the Permian-Triassic...