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  • Ecology & evolution

Published online: 10 January 2008 | doi:10.1038/nchina.2007.288

Extinction theory: A double episode

Wei Zeng

Introduction

© (2007) Geological Society of America

There has been much debate whether impact from an asteroid or global climate change was the cause of Earth's most severe mass extinction 250 million years ago. Shucheng Xie at China University of Geosciences in Wuhan and co-workers¹ have evidence that two prolonged periods of global warming at that time, most probably due to volcanic eruptions, might be the cause of the ecological crisis.

The researchers studied the radioactive-carbon level of marine sediments from Meishan in south China and identified two episodes of carbon decline (see image) that can be linked to the ecological crisis. The 'double episode' has been previously recorded in marine sediments of the same ecological era taken from the Carnic Alps in Austria and Shahreza in central Iran, indicating that the crisis was a global event.

The researchers showed that the first episode occurred before the asteroid was presumed to have made impact. They also showed that both episodes happened when there was widespread deposition of organic matter on the land and seafloor, mass extinction of fauna, and bloom of cyanobacteria (blue–green algae). These findings suggest that the atmosphere, land and sea were experiencing dramatic changes simultaneously. Volcanic eruptions are most likely to be the cause of the environmental changes, as shown by the abundance of black carbon fragments in the sediments.

The authors of this work are from:
Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, and State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China; Bristol Biogeochemistry Center, School of Chemistry, University of Bristol, Bristol, UK; School of Earth and Environment, University of Leeds, Leeds, UK.

Reference

1. Xie, S. et al. Changes in the global carbon cycle occurred as two episodes during the Permian–Triassic crisis. Geology 35, 1083–1086 (2007).  | Article |