  L1521E seems unique among starless cores. It stands out in a distribution of
a ratio (R) that we define to asses core evolution, and which compares the
emission of the easily-depleted C18O molecule with that of the hard to deplete,
late-time species N2H+. While all cores we have studied so far have R ratio
lower than 1, L1521E has an R value of 3.4, which is 8 times the mean of the
other cores. To understand this difference, we have modeled the C18O and N2H+
abundance profiles in L1521E using a density distribution derived from 1.2mm
continuum data. Our model shows that the C18O emission in this core is
consistent with constant abundance, and this makes L1521E the first core with
no C18O depletion. Our model also derives an unusually low N2H+ abundance.
These two chemical peculiarities suggest that L1521E has contracted to its
present density very recently, and it is therefore an extremely young starless
core. Comparing our derived abundances with a chemical model, we estimate a
tentative age of 1.5 x 10^5 yr, which is too short for ambipolar diffusion
models.
