Search for: All records

Abstract Determining causal relationships between environmental change and early animal evolution has been limited by our lack of a robust temporal framework for the Ediacaran Period (635-539 million years ago). Here we present six new radioisotopic age constraints from the Sultanate of Oman, which furnish a quantitative temporal framework for biogeochemical changes associated with animal radiation in the middle and late Ediacaran Period. In addition to constraining the duration of Earth’s largest negative carbon isotope excursion in its type locality, this temporal framework underpins a new understanding of Ediacaran sedimentation rates, a critical control on geochemical records and fossil preservation. Our new dates quantify early Ediacaran (prior to c. 574 million years ago) condensation in key sections across Gondwanan margins. This temporal framework highlights a pressing need to reassess proxy records of oxygenation—often hypothesized as a critical environmental constraint for the emergence of complex multicellular life—considering non-static sedimentation rates. 

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, there are a number of controversies surrounding the Shuram, including its timing, duration, and role in the concomitant biological and biogeochemical upheavals. Here we present radioisotopic dates bracketing the Shuram on two separate paleocontinents; our results are consistent with a global and synchronous event between 574.0 ± 4.7 and 567.3 ± 3.0 Ma. These dates support the interpretation that the Shuram is a primary and synchronous event postdating the Gaskiers glaciation. In addition, our Re-Os ages suggest that the appearance of Ediacaran macrofossils in northwestern Canada is identical, within uncertainty, to similar macrofossils from the Conception Group of Newfoundland, highlighting the coeval appearance of macroscopic metazoans across two paleocontinents. Our temporal framework for the terminal Proterozoic is a critical step for testing hypotheses related to extreme carbon isotope excursions and their role in the evolution of complex life.