  Milky Way-mass galaxies in the FIRE-2 simulations demonstrate two main modes
of star formation. At high redshifts star formation occurs in a series of short
and intense bursts, while at low redshifts star formation proceeds at a steady
rate with a transition from one mode to another at times ranging from 3 to 7
Gyr ago for different galaxies. We analyse how the mode of star formation
affects iron and alpha-element abundance. We find that the early bursty regime
imprints a measurable pattern in stellar elemental abundances in the form of a
"sideways chevron" shape on the [Fe/H] - [O/Fe] plane and the scatter in [O/Fe]
at a given stellar age is higher than when a galaxy is in the steady regime.
That suggests that the evolution of [O/Fe] scatter with age provides an
estimate of the end of the bursty phase. We investigate the feasibility of
observing of this effect by adding mock observational errors to a simulated
stellar survey and find that the transition between the bursty and steady phase
should be detectable in the Milky Way, although larger observational
uncertainties make the transition shallower. We apply our method to
observations of the Milky Way from the Second APOKASC Catalog and estimate that
the transition to steady star formation in the Milky Way happened 7-8 Gyrs ago,
earlier than transition times measured in the simulations.

Astrophysics of Galaxies