Mass extinction theories need more air
Some 250 million years ago, a mass extinction event took place which wiped out almost 95% of all species. The cause of this catastrophe is the subject of numerous theories. Now, new research findings from University College Dublin in Ireland are putting these theories through a trial by fire, literally.
Their findings, published in the journal Science, question the commonly held theory that declining oxygen levels served as a mechanism that led to the mass extinction.
The Permian-Triassic catastrophe which occurred 250 million years ago is considered to be the greatest of five mass extinctions that have ever occurred. According to experts, this catastrophe was responsible for exterminating almost 95% of all species, 53% of marine families, 84% of marine genera and an approximated 70% of all land species including plants, insects and vertebrate animals.
Many researchers believe that thinning levels of oxygen in the atmosphere were a leading cause of these extinctions.
According to the lead author of the report, Dr Claire Belcher, from the School of Biology and Environmental Science at University College Dublin, this theory now needs to be re-evaluated in light of their findings.
'Low oxygen atmospheres, [of] less than 12%, are considered to be the primary driver of at least two of the 'big five' mass-extinction events,' she explained. 'But our research findings question that hypothesis and highlight the need for more detailed studies of fossil charcoal across these mass extinction events.'
The research team in Dublin, which received funding from the EU through a Marie Curie Excellence Grant, tested the hypothesis that low oxygen levels were prevalent in the Mesozoic era in the millennia running up to the extinction. The researchers carried out a series of experimental burns in a specially designed walk-in plant growth room which was fully equipped with a thermal imaging system and a complete atmospheric, temperature and humidity control system.
The results of these experiments were then compared with all known geological evidence for wildfires such as the fossilised remains of charcoal. Their existence proves the presence of wildfires and therefore indicates that there was enough oxygen in the atmosphere for the fires to exist. If the oxygen levels are too low, there is simply not enough oxygen to feed the wildfires.
'By performing experimental burns using pine wood, moss, matches, paper and a candle at 20°C in varying ranges of oxygen concentrations and comparing these results to the occurrences of fossil charcoal throughout the Mesozoic (250-65 million years ago), we were able to identify that prolonged periods of low oxygen are unlikely to have occurred,' said Dr Belcher.
The research team has successfully shown that an extended period of low oxygen was not possible in the Mesozoic era. What is now needed is further research on all mass extinction events to further test the theory that a short term reduction in oxygen was responsible for mass extinction events.
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Category: Project results
Data Source Provider: Science, University College Dublin
Document Reference: Belcher, C et al. (2008), Limits for combustion in low O2 redefine paleoatmospheric predictions for the Mesozoic. Science, 321: 1197-1200
Subject Index: Earth Sciences; Scientific Research