Ice can sculpt extraordinary landscapes, yet the efficacy of, and controls governing, glacial erosion on geological timescales remain poorly understood and contended, particularly across Polar continental shields. Here, we assimilate geophysical data with modelling of the Eurasian Ice Sheet - the third largest Quaternary ice mass that spanned 49 degrees N to 82 degrees N - to decipher its erosional footprint during the entire last similar to 100 ka glacial cycle. Our results demonstrate extreme spatial and temporal heterogeneity in subglacial erosion, with rates ranging from 0 to 5mm a(-1) and a net volume equating to similar to 130,000 km(3) of bedrock excavated to depths of similar to 190m. A hierarchy of environmental controls ostensibly underpins this complex signature: lithology, topography and climate, though it is basal thermodynamics that ultimately regulates erosion, which can be variously protective, pervasive, or, highly selective. Our analysis highlights the remarkable yet fickle nature of glacial erosion - critically modulated by transient ice-sheet dynamics - with its capacity to impart a profound but piecemeal geological legacy across mid- and high latitudes.