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Learning about Mass Extinction Events

                             

A few days ago, there were major headlines and social media buzz relating to the space object A/2017 U1 coming towards earth at a speed of 156,400 km/h. It was first spotted as it flew past Jupiter, so if it were on a collision course with earth we would have had about 4 days to get our affairs in order. The dinosaurs didn’t even see the space object coming 65 million years ago. The K/T dinosaur extinction was the last mass extinction event to take place. A/2017 U1 missed us by 24 million kilometres. No worries!

I have a fascination with dinosaurs. I’m not alone. Young children identify with dinosaurs. Allen Dubois, in Dinosaur Memories, tells us that although they are frightening creatures of the imagination, they can be conquered. Unlike mythical dragons and movie monsters, dinosaurs were once alive. Dinosaurs also represent intellectual power for children as they learn the vocabulary and science of dinosaurs. I have friends who have turned this early interest in dinosaurs into careers in paleontology.

And so, it was particularly timely when the University of Calgary Gallagher Colloquium series featured Dr. David Bond from the University of Hull speaking about the earth's greatest extinctions and the future of life this week. I learned from him that mass extinctions result from more than just comets hitting the earth.

Demonstrating the skills of a scientist, Dr. Bond began his presentation with an operational definition so that we all knew what he meant by ‘mass extinction’. Extinction of the passenger pigeon was tragic and represented the loss of a massive number of birds, but it was the loss of a single species. To be a mass extinction, Bond tells us that there must be a loss of entire higher levels of taxa: entire families and perhaps some orders as well. I liked the way he illustrated his point by using the Ford family of vehicles. First a photo showed the Fords that existed in the 1950s – 70s. Then he removed the models that no longer exist and asked us if that was a mass extinction. He then followed up to show the Ford models that exist today as an example of how the loss of some car models was followed by a larger array of newer ones. The Ford family remains diverse and strong.

In his presentation, Bond spoke of the great example of science methods used by Luis and Walter Alvarez to propose the impact model for dinosaur extinction. Bond pointed out that while this model is widely accepted, there is still plenty of discussion about what other events may have been happening simultaneously to bring about mass extinction both on land and in the oceans.

Bond then went on to describe a relationship between ‘traps’ and mass extinctions. Traps, from the Swedish trappa meaning stairs, refer to massive volcanic rock flows. He noted that the Deccan Traps of India also occurred 66 million years ago and are associated with massive volcanism lasting for up to 30,000 years. Bond noted that there remains plenty of heated discussion among scientists regarding the contributions of each towards dinosaur extinction. He also informed us of the massive Siberian Traps which developed 250 million years ago from massive volcanism lasted for more than a million years. These traps were formed at the Permian-Triassic boundary associated with another mass extinction.

According to Dr. Bond, the major contributors to mass extinction are:
  • thermal stress
  • marine anoxia
  • ocean acidification
  • ozone layer depletion
  • acid rain
  • toxic poisoning
  • photosynthetic slowdown (darkness)
He was able to show how each of these result when there is massive volcanic activity such as the formation of the Siberian or Deccan traps. He also pointed out that there has been only the one mass extinction since the breakup of Pangea, but he said that relationship will require additional study.

Bond finished his presentation showing a series of sensational newspaper and website science-y headlines, and cautioned us about drawing big conclusions from small experiments.

Link of interest: On the causes of mass extinctions

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