  Observations of the Earth as a planet using the earthshine technique (i.e.
looking at the light reflected from the darkside of the Moon), have been used
for climate and astrobiology studies. They provide information about the
planetary albedo, a fundamental parameter of the Earth's energy balance. Here
we present for the first time, observations of the earthshine taken at high
spectral resolution. The high spectral resolution was chosen in order to
investigate the possibility of detecting metallic layers in the Earth's
atmosphere of geological or meteoritic origin. The SARG echelle spectrograph at
the Telescopio Nazionale Galileo in La Palma was used to acquire the earthshine
data. Observations were carried out on several nights in February 2011, with
the spectral resolution set at 29,000, covering a spectral range from the
near-ultraviolet (360 nm) to near-infrared (1011.9 nm). While we find evidence
for the detection of a Na layer in the earthshine, other atomic species are not
detected, perhaps due to the low signal-to-noise ratio of the observations and
the difficult telluric corrections. The Na layer is found to vary between
observation dates, which we speculate is due to physical variations in
mesospheric Na concentrations.
