Yorkshire Philosophical Society

Event Information

UV-B radiation was the terrestrial killer at the Devonian-Carboniferous boundary

John Marshall, School of Ocean & Earth Science, University of Southampton

Some 359 million years ago there was a terrestrial mass extinction at the boundary between the Devonian and Carboniferous Periods. Major extinctions include all the armoured fish and important groups within the land plants. In East Greenland there are a number of good localities where we can find the terrestrial extinction layer. These are in the arid centre of the Old Red Sandstone Continent some 1000 km from the sea. The boundary is found in a large deep wide lake that represents a highly active monsoon system showing the climate was globally warm. It is from these lake deposits that we can isolate the tough outer wall layers of pollen and spores that normally protect the cellular DNA from UV radiation. In the middle of the lake bed there are malformed pollen and spores that demonstrate that the extinction was coincident with elevated UV-B radiation and a reduced protective ozone layer. Mercury analyses show there is no evidence for continental scale volcanic eruptions as were responsible for the end Permian, end Triassic and Late Devonian mass extinctions. A possible cause of ozone loss is increased transport of naturally ozone destroying chemicals into the atmosphere. An important conclusion is that ozone loss during rapid warming is inherent in the Earth System and that we should be alert for the same process occurring in our rapidly warming world. Other suggested and now recently restated causes include a cosmic ray blast from an exploding star, i.e. a supernova.

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Members report

There have been several mass extinctions in Earth’s history, one of which occurred about 359 million years ago and killed much of the Earth’s plant and freshwater aquatic life. One of the best places to find the terrestrial extinction layer is in the mountains of East Greenland, where sedimentary evidence has been gathered from ancient lake beds at the boundary between the Devonian and Carboniferous Periods. Similar sites in the southern hemisphere can be found in Bolivia, which provide matching results. A key discovery of malformed pollen and spores in the samples, suggested that the extinction was caused by a probably brief breakdown of the ozone layer that shields the Earth from damaging ultraviolet light (UV-B). Cosmologists suspect the effects of supernova radiation, but this research suggests rapid warming of the atmosphere caused the release of ozone-damaging chemicals from organic material.

There was selective species survival: among them tetrapods, our own distant ancestors. An important conclusion for humanity is that ozone loss during rapid warming is inherent in the Earth’s system and that we should be alert for the same process occurring to our rapidly warming world today.’

Ken Hutson & Carole Smith

For more detail, see also https://www.sciencedaily.com/releases/2020/05/200527150158.htm