IAP-26-028

Investigating biogeochemical cycling in Archean and modern extreme environments

Earth’s sedimentary record contains widely accepted traces of life back to 3.5 billion years ago (Ga), however, relatively little is known about nutrient availability in these ancient ecosystems. It is widely debated what limited primary productivity in different environmental settings and how this shaped biological evolution. Some biogeochemical models argue for widespread phosphorus limitation (Rego et al. 2023), while others have proposed that phosphorus was abundant (Brady et al. 2022), and thus making nitrogen the biolimiting nutrient (Boden et al. 2026). New biogeochemical datasets are needed to better reconstruct the sources and sinks of these two major nutrients and the palaeoenvironmental conditions that control them.

This project aims to address this knowledge gap with new geochemical analyses of Paleoarchean rocks from shallow-marine evaporitic settings with extensive microbial mats and of modern analogue settings. New analytical methodologies will be applied to determine the speciation and cycling of phosphorus, including different phosphorus redox species (Baidya et al. 2025). We will also use carbon, nitrogen and sulfur isotopes, as well as redox-sensitive metals to determine nitrogen metabolism and redox conditions. Modern analogue settings will be considered to determine how nutrient cycles change under more extreme environmental conditions, such as evaporitic basins (e.g. Dilletoro et al. 2023) and/or hydrothermal environments.

– Geological sampling of drill cores and field sections
– Geochemical sample preparation in standard and clean laboratories
– Analyses of carbon (organic and inorganic), nitrogen and sulphur (sulphate and sulphide) isotopes as tracers of redox and productivity (e.g. Stüeken et al. 2024, Salisbury et al. 2025).
– Major and minor elemental analyses to establish sediment provenance and potential enrichments in redox sensitive proxies
– Optical microscopy, electron microscopy

Year 1

Literature review; preparation of pilot samples that are already available; training in laboratory techniques; fieldwork to undertake stratigraphic analysis and collect samples, compilation of first dataset; present poster at a regional conference

Year 2

Sampling campaign for additional ancient and modern analogue samples; write-up of first publication; continued data collection and compilation; present poster and/or talk at a national conference

Year 3

Complete data collection; focus on preparation of manuscripts for publication; present talk at an international conference

Year 3.5

Compilation of PhD dissertation constructed through the compilation of papers the student has written

The student will learn a suite of practical and transferrable skills including:
– Geological sample characterization
– Laboratory techniques for sample preparation
– State-of-the-art analytical techniques (IRMS, ICP-MS)
– Operation of mass spectrometers, familiarization with minor trouble-shooting and maintenance tasks
– Critical evaluation of the scientific literature
– Statistical data analysis and data management
– Scientific writing
– Project management
– Teamwork
– Science communication via written manuscripts, conference posters and oral presentations