These images and lots of good discussion about the
arguments for and against this evidence stemming
from life on Mars can be found at
Allan Tremaine's web site and
particularly his
Recent
Scientific Papers on ALH84001 Explained, with Insightful and
Totally Objective Commentaries.
Basically, the evidence lines up like this.
It is presently impossible to prove that the
signatures detected in the rock do NOT correspond
to life.
However, many people have shown alternate
interpretations for each of the individual
pieces of evidence that McKay et al. put
together to derive their conclusion of
relic life.
Several of the issues people are questioning
are how hot the rock was heated (the mineral
composition depends on this); if you can
make the organic molecules non-biogenically;
whether there was any terrestrial contamination
(either in Antarctica or in the lab);
how big are the smallest bacteria on Earth;
and other issues.
The summaries given on Allen Tremain's web page
are quite good and not
technical, and this would make a fascinating
term paper topic for someone (to examine both
sides of the issue and compare the arguments).