The rise of animals occurred during an interval of Earth history that witnessed dynamic marine redox conditions, potentially rapid plate motions, and uniquely large perturbations to global biogeochemical cycles. The largest of these perturbations, the Shuram carbon isotope excursion, has been invoked as a driving mechanism for Ediacaran environmental change, possibly linked with evolutionary innovation or extinction.
However, several controversies are surrounding the Shuram, including its timing, duration, and role in the concomitant biological and biogeochemical upheavals.
In a new study, scientists by the Yale and the Massachusetts Institute of Technology have determined the beginning and end dates of the Shuram carbon excursion. They have sorted out the timing of one part of the story, ruling it out as a cause of mass extinction of animal species.
Scientists studied rhenium-osmium (Re-Os) isotopes in ancient rocks. They wanted to determine that the Shuram event began 574 million years ago and ended 567 million years ago. The analysis showed the same timing for rocks in both Oman and Northwest Canada, indicating that Shuram was an asynchronous, global event.
This timing suggests the Shuram excursion was not responsible for a global mass extinction that almost stopped the evolution of animal life during the Ediacaran Period, which occurred from 635 to 541 million years ago.
Yale geologist Alan Rooney said, “For decades, the paleontological community believed that the Shuram event played a role in the appearance or extinction of some of the earliest animal life. Our new data refute that hypothesis. The Shuram event was not connected to the Ediacaran extinction — or the explosion of species that came later.”
Marjorie Cantine of MIT is the study’s other co-lead author. The study included co-authors from the Sultanate of Oman, Stanford University, and Dartmouth College.
- Alan D. Rooney et al. Calibrating the coevolution of Ediacaran life and environment. DOI: 10.1073/pnas.2002918117