The four main findings about the age and abundance structure of the Milky Way bulge based on microlensed dwarf and subgiant stars are : ( 1 ) a wide metallicity distribution with distinct peaks at [ Fe / H ] = -1.09 , -0.63 , -0.20 , +0.12 , +0.41 ; ( 2 ) a high fraction of intermediate-age to young stars where at [ Fe / H ] > 0 more than 35 % are younger than 8 Gyr , ( 3 ) several episodes of significant star formation in the bulge 3 , 6 , 8 , and 11 Gyr ago ; ( 4 ) the ‘ knee ’ in the \alpha -element abundance trends of the sub-solar metallicity bulge appears to be located at a slightly higher [ Fe/H ] ( about 0.05 to 0.1 dex ) than in the local thick disk .