  The two most prominent and ubiquitous features of glasses at low
temperatures, namely the presence of tunneling two-level systems and the
so-called boson peak in the reduced vibrational density of states, are shown to
persist essentially unchanged in highly stabilized glasses, contrary to what
was usually envisaged. Specifically, we have measured the specific heat of 110
million-year-old amber samples from El Soplao (Spain), both at very low
temperatures and around the glass transition Tg. In particular, the amount of
two-level systems, assessed at the lowest temperatures, was surprisingly found
to be exactly the same for the pristine hyperaged amber as for the,
subsequently, partially and fully rejuvenated samples.
