ABSTRACT Nearly all models of Earth’s oxygenation converge on the premise that the first notable rise of atmospheric oxygen occurred slightly above the Archean-Proterozoic boundary, with the second notable rise occurring just below the Proterozoic-Phanerozoic boundary. Plate tectonic–driven secular changes found above the Archean-Proterozoic boundary are thought to have been partly or wholly responsible for the initial rise in atmospheric O 2 in the Great Oxidation Event; however, the role of plate tectonics in oxygen levels thereafter is not well defined. Modern plate tectonics undoubtedly play a role in regulating atmospheric O 2 levels. Mountain building, for example, promotes high erosion rates, nutrient delivery to oceans, and efficient biogeochemical cycling of carbon, resulting in the net burial of organic carbon—thought to be the primary regulator of atmospheric O 2 levels on geological time scales. The trajectory of atmospheric O 2 and oceanic redox conditions in the Proterozoic Eon, representing almost 2 b.y. of geological history, shows a dynamic history with global trends that indicate overall high-low-high O 2 levels throughout the Proterozoic Eon, with low-oxygen conditions established by ca. 2.0–1.8 Ga. This contravenes the tenet that major orogenic events (e.g., the Himalaya-scale Trans-Hudson orogen and other coeval orogens that formed the supercontinent Nuna) should yield higher O 2 levels, not lower. The contrast of higher O 2 early in the Paleoproterozoic with lower O 2 later in the Paleoproterozoic is particularly striking, and mechanisms that might have caused this secular change remain unclear. This contribution explores feedbacks related to the tectonic evolution associated with the building of proto-Laurentia and Earth’s first supercontinent, Nuna, and how this impacted the trajectory of atmospheric O 2 in the latest Paleoproterozoic Era.