Â鶹ÒùÔº

Chengdu University of Technology-led research has established a high-resolution astrochronological framework spanning approximately 57.6 million years of the early Ediacaran Period. This calibrated timeline provides precise constraints on major climatic events and the appearance of early complex life, offering critical context for understanding environmental change and biological innovation during Earth's early history.

Understanding early life on Earth has been frequently stalled by an imprecise geological clock. Scientists have relied on broad stratigraphic patterns to trace the early Ediacaran Period (635 to 538.8 million years ago), a time marked by massive climate upheavals and the first signs of complex life.

Without consistent radiometric dating, researchers have struggled to align environmental disruptions such as shifts in carbon chemistry or marine oxygen levels with biological change. It's a bit like having a few puzzle pieces and a stack of puzzles they might have come from. Fragmented timelines have left unanswered questions about what may have triggered evolutionary steps and when they occurred.

In the study, "Astronomically calibrating early Ediacaran evolution," in Nature Communications, researchers applied astrochronology and magnetic susceptibility analysis to build a 57.6-million-year timeline of the early Ediacaran Period.

Astrochronology is a method used to date sedimentary rock layers by linking them to regular, predictable changes in Earth's orbit around the sun. Orbital variations, known as Milankovitch cycles, influence global climate over tens to hundreds of thousands of years.

As climate shifts, the type and amount of material deposited in oceans and lakes changes as well. Sedimentary patterns can be matched to known orbital cycles, allowing researchers to construct detailed timelines.

Magnetic susceptibility measures how much a rock responds to an external magnetic field. In marine sediments, this reflects the concentration of magnetic minerals that often originate from erosion on land or from chemical processes in the ocean. Higher values often indicate greater input of land-derived particles during wetter or more dynamic climate intervals.

By scanning sediment cores at high resolution, researchers created detailed profiles of how magnetic mineral content varied over time. Patterns were then aligned with orbital cycles as part of the astrochronological timeline.

Samples came from three drillcores recovered across the Yangtze Platform in South China. The sites were selected to represent a range of depositional settings, from shallow intrashelf basin to deeper slope environments. Together they span most of the lower and middle Doushantuo Formation, a rock unit deposited shortly after the Marinoan glaciation. Astrochronological tuning of the sedimentary cores uncovered several turning points in early Ediacaran history.

Sediment layering neatly matched known orbital cycles, producing a calibrated timeline anchored to the onset of the Gaskiers glaciation at 579.63 million years ago. Marinoan deglaciation events were constrained between 636.05 and 634.90 million years ago. Three large carbon isotope shifts, identified as EN1, WANCE, and EN2, were detected and sequenced across shallow to deep-water environments.

Carbon excursions aligned with stratigraphic evidence of biogeochemical disruption. EN1 and EN2 appeared globally and at consistent timescales, while WANCE was recorded only in South China. Across all three sites, differences in onset and duration suggested local variability in sedimentation yet maintained orbital pacing.

Fossil zones such as the Weng'an and Lantian biotas were fixed to precise points on the astrochronological scale. Patterns reflected stepwise ecological complexity without a measurable increase in overall diversity.

Updated age constraints resolve some long-standing uncertainties around when key environmental and biological changes occurred. For example, onset and termination of Marinoan deglaciation (636.05 and 634.90 million years ago) narrow the previously wider, debated ranges. EN1 and EN2 were shown to occur globally and at consistent timescales, confirming their use as synchronized geochemical timepoint markers.

Complex multicellular life in the Weng'an biota can now be dated to approximately 589.89 million years ago, during the interval marked by the WANCE carbon isotope excursion. Additional fossil groups were tied to separate carbon isotope events, showing that biological innovation emerged in phases connected to these disruptions.

Correlations among orbital pacing, isotope shifts, and fossil turnover offer a testable framework for linking early life to planetary change at both regional and global levels.

© 2025 Science X Network