  Micron-sized stardust grains that originated in ancient stars are recovered
from meteorites and analysed using high-resolution mass spectrometry. The most
widely studied type of stardust is silicon carbide (SiC). Thousands of these
grains have been analysed with high precision for their Si isotopic
composition. Here we show that the distribution of the Si isotopic composition
of the vast majority of stardust SiC grains carry the imprints of a spread in
the age-metallicity distribution of their parent stars and of a power-law
increase of the relative formation efficiency of SiC dust with the metallicity.
This result offers a solution for the long-standing problem of silicon in
stardust SiC grains, confirms the necessity of coupling chemistry and dynamics
in simulations of the chemical evolution of our Galaxy, and constrains the
modelling of dust condensation in stellar winds as function of the metallicity.
