This PhD work focused on novel geochemical and isotopic signatures preserved in chemical sedimentary rocks and other marine sediments from the Canadian Superior Craton, deposited between 2.93 and 2.8 Ga, to better understand the evolution of photosynthetic pathways on the early Earth. Iron isotopechemostratigraphy of stromatolitic carbonates and deep-water sediments preserved in drill core from the 2.93 Ga Red Lake Greenstone Beltreveals complex iron redox cycling across a shallow-to-deep transect, with coupling between Fe and S cycling that is best explained by offshorephotosynthetic activity. Comparative REE systematics of three Mesoarchean carbonate platforms of the Superior Craton (2.93 Ga Red Lake, 2.86 Ga Woman Lake, and 2.80 Ga Steep Rock Lake) and representing Earth’s earliest known large carbonate platforms, provide clear evidence for estuarine processes,hydrothermal inputs, and crucially, for the production of free oxygen, as tracked by important negative Ce anomalies of unprecedented magnitude for the Archean. High-precision La-Ce geochronology was successfully applied to samples from all three sites, yielding three clear isochrons that constrain the timing of La/Ce fractionation, and thus Ce oxidation, to the time of deposition. These results constitute the first geochronological constraint on the origin of oxygenic photosynthesis and place it firmly within the Mesoarchean, with important implications for our current understanding of Earth’s biological and geochemical evolution.