2007MNRAS.379..807R

We demonstrate how the observed H₂ O ice column densities toward three dense globules in the Southern Coalsack could be used to constrain the ages of these sources. We derive ages of ∼10⁵ yr, in agreement with dynamical studies of these objects. We have modelled the chemical evolution of the globules and showed how the molecular abundances are controlled by both the gas density and the initial chemical conditions as the globules formed. Based on our derived ages, we predict the column densities of several species of interest. These predictions should be straightforward to test by performing molecular-line observations.