The tempo of Ediacaran evolution.

Area of Science:

• Paleontology and Geochemistry
• Earth and Environmental Science

Background:

• The Ediacaran Period saw the emergence of complex life amidst significant biogeochemical changes.
• Existing chronostratigraphic frameworks lack the resolution to link these changes to evolutionary events.
• Understanding the Ediacaran timeline is crucial for deciphering the role of biogeochemical cycles in early complex life evolution.

Purpose of the Study:

• To establish a high-resolution chronostratigraphic framework for the Ediacaran Period.
• To correlate key fossil assemblages with major carbon cycle perturbations.
• To test hypotheses on the influence of biogeochemical cycling on the evolution of complex life.

Main Methods:

• Radio-isotopic dating of Ediacaran strata.
• Integration of new dates with global correlation schemes.
• Analysis of carbon isotope excursions.

Main Results:

• New radio-isotopic dates provide precise age constraints for Ediacaran fossil assemblages and carbon cycle events.
• Late Ediacaran strata in South China are time-transgressive.
• Two significant negative carbon isotope excursions (Shuram and a younger event) occurred between 575 and 550 million years ago.

Conclusions:

• The refined chronostratigraphic framework calibrates the pace of Ediacaran evolution.
• Ecosystem complexity increased over tens of millions of years, punctuated by biological turnovers.
• These turnovers coincide with major disruptions in the carbon cycle, highlighting its role in evolutionary events.