Since the beginning of Earth’s history, the oceans acted as an interface between the atmosphere, the continents, and the mantle via atmospheric exchange, weathering, sedimentation, and submarine volcanism. Such interactions make the composition of early seawater a unique recorder of the processes that have affected the Earth’s major reservoirs. Yet, this record has not been explored in details.

Here, I propose to investigate the geochemistry of the first oceans that is recorded in Precambrian banded iron formations (BIFs) to address first-order questions related to the early evolution of our planet. The proposed project combines well-established radiogenic isotopic systems with novel and highly promising stable isotope tracers that will be developed as part of the project. These geochemical proxies will be measured on a unique collection of BIF samples deposited from ~3.8 to 0.7 Ga ago with the following objectives:

(1) determine the origin, composition, and size of the first continents,

(2) detect whiffs of oxygen in the early oceans in various depositional settings before and after the Great Oxidation Event (GOE),

(3) identify the periods of intense hydrothermal activity through Earth’s history and link them to global mantle geodynamics.

The proposed project will promote the application of state-of-the-art isotopic measurements, with an emphasis on further methodological development to set-up new isotope proxies. This innovative approach is needed to test previously suggested hypotheses, develop new ideas, and to tackle the challenging questions of the early Earth evolution from a different angle.