It is interesting to note that, in the Wikipedia article, it
states that The amino acids were racemic (that is, the chirality
of their enantiomers are equally left- and right-handed),
indicating that they are not present due to terrestrial
contamination". This implies that, if a 'life form' did create
these proteins, they are fundamentally quite different to life
on earth. (Particularly in light of the 70 unique amino acids
they described!). We cannot ever 'know' how they were made,
unless a pretty revolutionary discovery is made that
undisputably confirms evidence for extra-terrestrial life
(although this is the best evidence yet!), so we are left to
speculation. The nucleobases either formed 'randomly' in one of
the countless celestial events (although the chances of this
seem pretty remote given the complexity of the molecules and the
homogeneity in the sample), or they were made by extra-
terrestrial 'life' (much more exciting, and indeed probably more
likely, as we will see). (Or the 3rd option: intellige