Calibrating the coevolution of Ediacaran life and environment

Area of Science:

• Paleontology and Geochronology
• Biogeochemistry and Earth System Science

Background:

• The Ediacaran period witnessed the rise of animals amidst dynamic Earth conditions, including significant perturbations to global biogeochemical cycles.
• The Shuram carbon isotope excursion is a major perturbation, but its timing, duration, and role in Ediacaran environmental and evolutionary changes are debated.

Purpose of the Study:

• To establish a precise radioisotopic age for the Shuram carbon isotope excursion.
• To investigate the temporal relationship between the Shuram excursion and the appearance of Ediacaran macrofossils.
• To provide a robust temporal framework for the terminal Proterozoic to test hypotheses on early animal evolution.

Main Methods:

• Radioisotopic dating (U-Pb) of sedimentary rocks bracketing the Shuram excursion on two paleocontinents.
• Re-Os (Rhenium-Osmium) geochronology to date macrofossil occurrences.
• Correlation of geochronological data to establish a global temporal framework.

Main Results:

• Radioisotopic dates indicate the Shuram excursion was a global and synchronous event occurring between 574.0 ± 4.7 and 567.3 ± 3.0 Ma, postdating the Gaskiers glaciation.
• Re-Os ages reveal the coeval appearance of Ediacaran macrofossils in northwestern Canada and Newfoundland, suggesting widespread metazoan diversification.
• A refined temporal framework for the terminal Proterozoic has been established.

Conclusions:

• The Shuram excursion was a synchronous, global event, providing a key marker for terminal Proterozoic Earth history.
• The timing of the Shuram excursion aligns with the widespread appearance of macroscopic metazoans, supporting its potential role in evolutionary innovation.
• This study provides critical temporal constraints for understanding the interplay between major environmental changes and the evolution of complex life.