Use the graph below to find out what the climate was like on Earth when each of its five mass extinctions occurred.

The red portions of the line charting past temperatures represent "hothouse" climate regimes, when there were no glaciers on Earth.

Note that these are only AVERAGE temperatures. The highest actual temperatures were so hot that even moss could not survive in an equatorial swamp. The north pole was so warm that ferns and palms thrived there.

The blue portions of the temperature line represent "icehouse" climate regimes, when there was extensive glaciation (as there is today, though this is rapidly changing due to human-caused global warming).

Again, these are AVERAGE temperatures. The lowest actual temperatures were so cold that all the world's oceans froze over. There were times when, to an observer in space, the planet would have looked like a giant snowball.

The dividing line between the two regimes is an average global temperature of about about 68°F.

For comparison, the average global temperature during the last thousand years or so has been about 57°F. This is the kind of world that we and our recent ancestors have learned to survive in.

Now find the places on the temperature line that correspond to the following historical events.

The Ordovician-Silurian Extinction occurred about 440 million years ago.

The Devonian Extinction occurred around 365 million years ago.

The Permian-Triassic Extinction happened about 250 million years ago. This event was precipitated by unusually high volcanic activity, which pushed atmospheric CO2 concentrations so high, feedback loops triggered a runaway greenhouse effect. 95% of all species then living on the planet died out.

The Triassic-Jurassic Extinction took place around 210 million years ago. The most widely-held theory of this event proposes that volcanic activity pumped enough CO2 into the atmosphere to greatly amplify the greenhouse effect and drastically raise temperatures. While in the hothouse regime, the temperatures for that time reflected on this graph do not look like a spike.

The Cretaceous-Tertiary extinction occurred around 65 million Years Ago. This event, which was caused by an asteroid impact, which left the planet shrouded in a cloud of dust that blocked out the sun for years, causing the demise of most dinosaurs (but not the ancestors of modern birds).

Which mass extinction does not fit the general pattern?

Devise a rule of thumb for predicting when a mass extinction is likely to occur.