Researchers studying rocks in India discovered chemical evidence of a series of rapid climate fluctuations during the greatest known mass extinction event, which occurred around 252 million years ago. Michael Brookfield of the University of Texas at Austin in the United States, along with colleagues in Taiwan, publish their findings and interpretations in the Journal of Asian Earth Sciences.
The extinction occurred at the geological boundary between the Permian and Triassic periods and is estimated to have eliminated more than 90% of marine species and 70% of land-based species. It is one of the most important events in the history of evolution, known colloquially as the Great Dying and academically as the Permian-Triassic Extinction.
Planetary scientists and biologists interested in the causes and timescale of extinction are investigating various competing and sometimes overlapping theories. Their research could be relevant to the threat that human activity poses to the current diversity of species on Earth.
Brookfield and colleagues investigated variations in the levels of carbon-13 and oxygen-18 isotopes, which are specific forms of carbon and oxygen atoms. Carbon isotope levels are thought to indicate how much carbon was incorporated into living organisms, whereas oxygen isotope levels are thought to vary with temperature.
The team collected samples along a ridge in the Guryul Ravine in Kashmir, India, where rocks formed during the Permian-Triassic transition.
The isotope record suggests previously unknown large but geologically short-term fluctuations in temperature, thus climate, and biological carbon incorporation during the mass extinction.
The authors conclude that major extinction events were caused by climate-linked changes in the chemistry of the atmosphere and oceans, rather than physical geological changes as suggested by other proposals. Evidence of climate change’s ability to cause ancient extinctions may be relevant to the climate change issues we face today.