Newsletter of the Geological Society of Norfolk

Number 58, September 2003

This little beast, a Lystrasaurus, was lucky enough to be the only herbivore known to survive the end-Permian extinction. This is probably fortunate for us because he was related to our ancestral line at that time!

The Review this time is ….

The book “When Life Nearly Died. The greatest mass extinction of all time”. Michael J Benton, Thames & Hudson, 2003.

and the paper “How to kill (almost) all life: the end-Permian extinction event”. Trends in Ecology & Evolution 18, July 2003, M J Benton & R J Twitchett.

At depth beneath Norfolk there are only a few rocks of Permian age; at that time Norfolk was on the northern edge of the London-Brabant Massif. Lystrasaurus probably walked here! However it has long been recognised that there was a major global extinction event at the end of the Permian, now known to be at 251 Ma. This subject interests many Earth Scientists but in this country Dr Wignall (Univ. of Leeds) and Prof. Benton (Univ. of Bristol) have been pre-eminent.

Prof. Benton has obviously put a lot of scholarship into an excellent book that is very readable. The author recognises that nothing in science is immutable and professes himself unconcerned if his book eventually finishes up discredited and collecting dust; but for the time being he advances interpretations by himself and other workers that add up to a coherent consistent picture. In the book the reader is introduced into each topic from an historical perspective and it is easy to appreciate how advances in Earth Science have been made, and with Prof Benton’s explanations no pre-existing really specialised knowledge is needed. This makes it attractive to the scientifically literate general reader.

At one time the extinction was thought to be a gradual process over as much as 10 million years that mainly took place in the seas but recent research and modern techniques have shown that it was much more sudden in geological terms and occurred everywhere. As much as 95% of all species on Earth were lost! This makes it the most catastrophic event known, far worse that that wiped out the dinosaurs at the end of the Cretaceous.

Life had had it good during the Carboniferous and most of the Permian. Oxygen levels in the atmosphere had reached an all-time high, vast coal-generating forests had clothed the Pangaean Continent and the seas were teeming with life. But it seems that at the end of the Permian there was a catastrophe. Some workers profess to have found evidence of an asteroid impact but others contest the data. Instead Prof. Benton finds the likely impact of the gaseous emissions from the basaltic lavas of the Siberian Traps a more like likely culprit. By extrapolating from similar eruptions in places like Iceland it is possible to calculate the amount of sulfur dioxide and carbon dioxide that would have been emitted. In such eruptions the SO₂ (and other acid gases) usually has little effect (except locally) since it is quickly washed out of the atmosphere by rain, but even the comparatively small Icelandic eruptions have emitted sufficient CO₂ to disturb the climate of the northern hemisphere to a discernable degree for a few years. New evidence about the rapidity of the Siberian eruptions (over just 600,000 yrs) just at the Permo-Triassic boundary indicate that the planet’s biomass would have been considerably stressed. Normal compensatory feedback mechanisms could not compensate sufficiently. Shortly after there was a marked change in the carbon isotope ratios indicating release of considerable amounts of ¹²C in quantities greater than can be explained by decomposition of the biosphere; and the only credible source is methane hydrates. Changes in oxygen isotope ratios are consistent with a subsequent 6^oC temperature rise resulting from the exaggerated greenhouse effect. Even if you are suspicious of catastrophes this book is well worth reading. What a great subject. Highly recommended.

For those who don’t need the techniques explaining, Prof. Benton has written the paper that contains the essence of the book.