The search for a solution to the origin of life puzzle is hindered by the impossibility
of providing an ultimate experimental proof, namely to (re)produce life
from scratch de novo (see e.g. [58,218]). In view of this obstacle, Wächtershäuser
[227] has suggested that the hypotheses on the origin of life could be validated
by rigorous application of Karl Popper’s principles of testing scientific theories
[228,229]. Popper wrote: “We may if we like distinguish four different lines along
which the testing of a theory could be carried out. First there is the logical comparison
of the conclusions among themselves, by which the internal consistency of the system
is tested. Secondly, there is the investigation of the logical form of the theory, with the
object of determining whether it has the character of an empirical or scientific theory,
or whether it is, for example, tautological. Thirdly, there is the comparison with other
theories, chiefly with the aim of determining whether the theory would constitute a
scientific advance should it survive our various tests. And finally, there is the testing
of the theory by way of empirical applications of the conclusions which can be derived
from it” (quoted from ref. [229]). The core of Popper’s approach is the idea of
falsification, i.e. putting a hypothesis to the test by making testable predictions
and checking them. The falsification tests of the Zn world hypothesis, because
of their key importance, are described in a separate accompanying article [226].
Here I consider only the empirical supporting evidence, the internal consistency
of the hypothesis, and the relation of the posited concept to other hypotheses on
the origin of life.