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The single stable isotope of beryllium is a pure product of cosmic-rayspallation in the ISM. Assuming that the cosmic-rays are globally transportedacross the Galaxy, the beryllium production should be a widespread process andits abundance should be roughly homogeneous in the early-Galaxy at a giventime. Thus, it could be useful as a tracer of time. In an investigation of theuse of Be as a cosmochronometer and of its evolution in the Galaxy, we foundevidence that in a log(Be/H) vs. [alpha/Fe] diagram the halo stars separateinto two components. One is consistent with predictions of evolutionary modelswhile the other is chemically indistinguishable from the thick-disk stars. Thisis interpreted as a difference in the star formation history of the twocomponents and suggests that the local halo is not a single uniform populationwhere a clear age-metallicity relation can be defined. We also found evidencethat the star formation rate was lower in the outer regions of the thick disk,pointing towards an inside-out formation.

Beryllium abundances and the formation of the halo and the thick disk