Zombie Science 1: Asteroid kills dinosaurs

By April 8, 2017Science

No, this is not an article on the study of the undead, it is about science which gets a run in the newspapers and on television, but has been or is being given the boot by real scientists who actually work in the fields concerned. This is largely about ignorance on the part of your average journalist, or even a ‘science’ journalist.

One of the classics of zombie science is the “asteroid that caused the extinction of the dinosaurs”. This gets a wide run in all sorts of newspapers1, television2 and radio3 shows. There are two problems with this: firstly, dinosaurs aren’t extinct; and secondly, it is extremely unlikely that they were wiped out by an asteroid hitting the planet.

Numerous fossil dinosaur species have been found which have incontrovertible evidence of feathers4. So, the feature which, in the general public’s imagination, separated the birds from the supposed reptilian dinosaurs is now known to be meaningless, as many dinosaurs among what are commonly called theropods had feathers, possibly even Tyrannosaurus rex! The theropods comprise the group within which birds arose. So, if you exclude birds from the Dinosauria, then you would have to exclude such quintessential carnivorous dinosaurs as Velociraptor, Utahraptor and all other Dromaeosaurs5.

The reason that the asteroid impact theory of dinosaur extinction became so popular, was because the impact of a huge asteroid, estimated to have been 10 km across, occurred just across the Gulf of Mexico from the southern United States. In the US, the evidence for severe effects of this impact is very common. This evidence includes shocked quartz grains, glass beads (quenched molten rock), as well as huge deposits of coarse rock fragments suspected to have been deposited by a tsunami6. In many places around the world, there is also a thin layer of clay, high in the element Iridium. Iridium is uncommon on the Earth’s surface and such a large concentration is almost certainly of extraterrestrial or volcanic origin. However, while the thin clay layer is widespread, none of the other evidence of catastrophic effects extends far beyond the region surrounding the impact structure. Furthermore, it seems likely that the Chicxulub impact event predates the extinction event by at least 100,000 years7.

The event which most likely caused the extinction of the non-theropod dinosaurs was the eruption of the Deccan Traps. This is a large long-term volcanic eruption in western India in which about 8.6 million cubic kilometres of continental flood basalt were erupted, along with an enormous amount of gas. The duration of this eruption is still unclear, but it apparently started about 250,000 years before the extinction event and led to significant environmental change that culminated in the mass extinctions on land and in the ocean8. These environmental changes included rapid global warming on land (~8 degrees C) and in the ocean (~4 degrees C), and concomitant ocean acidification9. Given the various scenarios for future global warming, this is worrying.

Sources

  1. https://www.nytimes.com/2016/11/18/science/chicxulub-crater-dinosaur-extinction.html
  2. https://www.youtube.com/watch?v=vuet3t9geXo
  3. http://www.abc.net.au/radionational/programs/breakfast/the-asteroid-that-sparked-the-extinction-of-the-dinosaurs/7291002
  4. https://en.wikipedia.org/wiki/Feathered_dinosaur
  5. https://en.wikipedia.org/wiki/Dromaeosauridae
  6. https://en.wikipedia.org/wiki/Chicxulub_crater
  7. https://gsa.confex.com/gsa/2014AM/finalprogram/abstract_244245.htm
  8. Schoene, B. et al., 2015. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science 347, 182-184
  9. http://adsabs.harvard.edu/abs/2015EGUGA..17.6774K

 

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