MW-based star-forming [O/Fe] versus sSFR relation. The big data point corresponds to the present-day MW, where the light grey extension of the error bars indicates the systematic uncertainty (see text and Table E.1). Grey points: [O/Fe] of the MW disc MS turn-off stars from GALAH DR3 with sSFR estimated from stellar ages assuming constant MW disc star formation history. Contours enclose 50%, 68%, and 95 % of stars in the diagram. Black empty squares indicate the average [O/Fe] of those stars grouped in 14 age bins (see Table B.1). Orange curves show part of the MW evolutionary track in the diagram reconstructed using binned ages and average [O/Fe] for different assumptions about the disc star formation history (see text for the details). The horizontal hatched bar at [O/Fe] ≈ 0.52 dex shows the average abundance ratio of the MW thick disc/halo dwarf stars with [Fe/H] < −2 from Amarsi et al. (2019) (x-axis value is arbitrary).