IAP-24-112

The origin of animals: Building a precise timeline from the geological record

The Ediacaran–Cambrian transition saw the evolutionary appearance of complex macroscopic life and animal-dominated ecosystems. Yet, basic questions on the timing and sequence of evolutionary events during that period remain unresolved, due to the challenge of correlating a geological record that straddles multiple continents¹. Signatures of ocean chemistry, such as stable carbon isotopes (δ13C), in principle allow for the correlation of fossil-bearing sedimentary sections from different locations. However, such chemostratigraphic signals are typically aligned by visual inspection, and may not exclusively represent a global oceanic signature. As such, this inherently subjective approach often produces multiple possible alignments, and gives no rigorous way of determining the most likely alignment, or quantifying uncertainty².

This project will use the StratoBayes correlation software to produce an objective stratigraphic framework of late Ediacaran–early Cambrian deposits, which will provide a definitive timeline of early animal evolution at an unprecedented temporal resolution. StratoBayes is a novel tool developed by members of the supervisory team³; it uses innovative Bayesian models to derive correlations between stratigraphic sections based on the geochemical signatures they record.

Starting from our existing compendium of Cambrian data, the successful student will compile a database of geochemical signals from the upper Ediacaran period. These data will be combined with new high resolution geochemical and radioisotopic data from Namibian cores obtained from the international GRIND drilling project (co-led by Rose)⁴, which offer a continuous and pristine record through the upper Ediacaran. StratoBayes will allow stratigraphic data to be combined across different palaeocontinents within a Bayesian framework, yielding precise dates (and associated uncertainties) for poorly constrained fossil sites and clarifying the sequence of the key evolutionary events that set the stage for complex animal ecosystems. Evaluating candidate index fossils and constraining Ediacaran–Cambrian stratigraphy will enable evolutionary research to resolve fundamental questions, such as whether early animal evolution was concentrated in one or multiple bursts; and inform how environmental changes served as triggers for, or were consequences, of animal evolution.

OBJECTIVE ONE: Precise correlation of late Ediacaran–early Cambrian δ13C records

The first phase of the project will integrate δ13C data from multiple continents to create a global reference curve spanning the Ediacaran–Cambrian transition.

1. Expand an existing database of stratigraphic data from early Cambrian strata to incorporate newly published Cambrian datasets, and data from late Ediacaran successions.

2. Use the StratoBayes correlation software to build regional correlations of δ13C records, identifying and quantifying uncertainties. Assign probabilities for different candidate alignments. Identify further data sources to resolve potential ambiguities.

3. Extend the regional correlations to produce a unified global correlation.

OBJECTIVE TWO. Improved age model of the Ediacaran–Cambrian transition

This phase will place the δ13C reference curve in the time dimension by incorporating radiometric dates.

1. Integrate radiometric dates with δ13C records across palaeocontinents to assign precise ages to individual horizons within key stratigraphic sections.

2. Evaluate age models against astrochronological information, exploring opportunities to incorporate evidence of cyclicity to improve the precision of reconstructed ages.

3. Combine stratigraphic and contextual factors to identify unaccounted sedimentation rate variability. Use these observations to improve correlations and the underpinning models.

OBJECTIVE THREE. High-resolution timeline of early animal evolution

The project will ultimately apply the age model to the fossil record to determine the sequence and rate of evolution across different environmental settings. This will make it possible to distinguish evolutionary change through time from non-uniform geological influences such as depositional setting and preservational regime.

1. Integrate fossiliferous sections into the global age model to obtain probability distributions on the first and last occurrences of evolutionarily significant taxa and faunas

2. Test for enhanced rates of extinction in Ediacaran fauna towards the base of the Cambrian

3. Test for synchronicity between origination, extinction and evolutionary change across geographic and environmental settings

4. Explore possible evolutionary drivers by establishing the temporal relationships between evolutionary events, including environmental changes and first and last occurrences.

Data will be obtained from the literature, from unpublished data compilations, and through the student’s own examination of drill core material. The student will also undertake fieldwork in Namibia to obtain training on the interpretation and collection of stratigraphic and geochemical data.

Bayesian analysis will be conducted in StratoBayes. Full training in necessary programming skills, data interpretation and processing, and model development will be provided by the supervisory team.

Year 1

Compilation of stratigraphic data and review of existing stratigraphic literature.
Introduction to StratoBayes; training in statistical modelling and implementation.
Fieldwork and training in interpretation and analysis of stratigraphic data (Bowyer, Rose).
Production of initial regional correlations from compiled dataset.

Year 2

Production of global stratigraphic correlation; incorporation of age data to construct age model. Integration of cyclostratigraphic information. Presentation of Year 1 Results at e.g. International Congress on Stratigraphy.

Year 3

Application of age model to palaeontological data. Presentation of Year 2 Results at e.g. EGU conference.

Year 3.5

Preparation of thesis; publication of papers. Presentation of Year 3 results at e.g. Palaeontological Association annual meeting.

Training & Skills
The student will benefit from fortnightly, interdisciplinary meetings of Smith’s research group, comprising Earth scientists, archaeologists and mathematicians. Research visits to St. Andrews (Rose), Leeds (Bowyer) and Dublin (Sinnesael) will equip the student with expertise on the geological and stratigraphic background of the Ediacaran–Cambrian, and on cyclostratigraphy. The student will be taught state-of-the-art analytical methods, Bayesian modelling and programming (Smith, Millard, Eichenseer). Additional computing training will be obtained by Durham’s Advanced Research Computing team, including training on using supercomputers, preparing the student for a career within or outside Academia. Attending workshops on stratigraphy and age modelling will provide additional training, and speaking skills and networking will be developed at scientific conferences.