The "Big Five" mass extinctions of the Phanerozoic Eon have long attracted significant attention from the geoscience community and the public. Among them, the Late Ordovician Mass Extinction (LOME) is the earliest of the Phanerozoic, and questions about its causes and dynamics have been a central focus in Earth sciences over the past century.

Traditionally, the duration of LOME was estimated at 1–2 million years. However, the use of advanced high-precision zircon U-Pb dating techniques shows that the extinction occurred on a much shorter timescale, spanning hundreds of thousands of years.

This research, published in Science Advances, was conducted by an international research team led by Prof. LI Xianhua from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (CAS) and Prof. RONG Jiayu from the Nanjing Institute of Geology and Palaeontology of CAS.

In bioenvironmental evolution, LOME exhibits a distinct two-stage pattern: the first stage (LOME I) coincided with abrupt global cooling and the rapid onset of the Hirnantian glaciation, while the second stage (LOME II) occurred after the glaciation ended and was accompanied by rapid global warming. Although a clear temporal correlation exists between LOME phases and changes in climate, the lack of precise geochronological control has prevented accurate determination of its timing and tempo, thereby limiting insights into the feedback mechanisms between climate change and mass extinction.

To resolve the timing and tempo of LOME, the researchers conducted a comprehensive geochronological study. They used chemical abrasion-isotope dilution-thermal ionization mass spectrometry zircon U-Pb dating techniques to obtain high-precision dates from ash beds in the Ordovician–Silurian transitional stratigraphic sections in the South China block, including the Global Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage at Wangjiawan North, Yichang, Hubei Province.

Integrating geochronology, biostratigraphy, carbon isotope chemostratigraphy, and biodiversity data, the team reconstructed the timing and tempo of LOME. They precisely determined the absolute ages of the Katian–Hirnantian boundary (442.65+0.17/−0.23 Ma) and the Ordovician–Silurian boundary (442.33+0.34/−0.33 Ma), constraining the duration of the Hirnantian Stage to approximately 320 kyr and providing key chronological data for updating the International Chronostratigraphic Chart.

With this refined chronology, the researchers revealed that LOME began at 442.76+0.35/−0.22 Ma, lasted approximately 400 kyr, and displayed a distinct two-stage pattern. LOME I lasted 340 kyr, during which the global climate shifted from a greenhouse state to the Hirnantian glaciation, with a cooling magnitude of 9 °C and an average cooling rate of 2.6 °C per 100 kyr. The average species extinction rate during this phase was 8.4% per 100 kyr. In contrast, LOME II lasted ~60 kyr and was marked by a rapid shift from an icehouse to a greenhouse climate, with a strikingly high average warming rate of 12.2 °C per 100 kyr. During this period, the average species extinction rate drastically increased to 71.6% per 100 kyr. This study quantitatively demonstrates the dominant role of the rate of climate change in controlling the pace of extinction.

In summary, this study establishes a precise absolute chronological timescale for the Ordovician–Silurian transition, refines the duration and tempo of LOME, and reveals that the rate of climate change was the main driver of its tempo. These results provide new perspectives on the interactions between the rate of environmental change and biological evolution in Earth's history.

The CAS scientists collaborated with researchers from the British Geological Survey, Peking University, University College London, and Hefei University of Technology on this study, which was supported by the Strategic Priority Research Program (B) of CAS, the National Natural Science Foundation of China, and the UK Natural Environment Research Council.

Ordovician sea life. (Image credit: Fritz Geller-Grimm / National Museum of Natural History / CC BY-SA 2.5.)