Extinction!

Perhaps the best known is the series of eruptions that took place on the Indian subcontinent beginning at the very end of the Maastrichtian stage, 66.5-64.5 million years ago. They poured out over one million cubic kilometres of lava in just over one million years, forming the vast Deccan Traps. The eruption did not take place continuously over the entire million years, but episodically in massive lava flows that have no counterpart in human history.

Since we have no direct experience of such cataclysmic eruptions, it is difficult to imagine (much less model) the climatic effects. Regardless, the close association between the flood-basalt record and the pattern of extinction events is very difficult to explain away as mere coincidence. In addition, it’s worth noting that the three largest extinctions of the last 250 million years took place during times of combined sea-level fall and flood-basalt eruption. Of course, the Maastrichtian event is also associated with the Chicxulub impact. However, this event is by no means the largest mass extinction to have occurred and, according to available data on the timing and magnitudes of impacts, several extinction events of equal and greater magnitude are not associated with large asteroid impacts.

Weighing up the evidence

As far as any single extinction event is concerned, in all probability we will never know all the factors involved. Nevertheless, the existing data provide an insight into the factors that are repeatedly associated with extinction events in the geological record.

A simple statistical analysis of the data in Figure 2 reveals the relative strength of the association between each type of catastrophe and mass extinctions as follows:

• sea-level change 7 out of 14
• continental flood basalt eruptions (over the last 250 million years) 10 out of 10
• asteroid impact 1 out of 17.

Based on current data, tectonic factors - giving rise to flood-basalt volcanism and sea-level fall - appear to exhibit the greatest level of association with large-scale extinction events over the course of the last 600 million years.

Extraterrestrial impacts - current darlings of the media coverage of extinctions - have certainly played an important role in Earth history and may have enhanced the ‘death of the dinosaurs.’ However, asteroid impacts do not appear to be the primary agents responsible for the overall patterns in the geological extinction record.

For more information

Video: Armageddon [ Firstscience presents]
What are the chances of being hit by a killer asteriod? This film analyses all of the evidence, all of the odds, and predicts the day that the world will end.