This conclusion seems reasonable. So, they presumed they had a meteor from Mars. Next they looked for evidence of life on and in the crevices of the meteor. They found two types of molecules that can form as a result of life processes, carbonates and complex molecules called polyaromatic hydrocarbons or PAHs. They also found shapes in the rock that resembled those of known microfossils on Earth.
Microfossils are fossils of one-celled organisms which are rather tricky to interpret.
Obviously, the NASA scientists felt the things just mentioned provided ample evidence to conclude that life once existed on Mars. However, the chemical signs could all be due to processes that have nothing to do with life, and the supposed microfossils are 100 times smaller than any such fossil found on Earth. The evidence is very equivocal and was challenged by many other scientists, but the media did not report that as fully. In fact, there is one simple explanation that is consistently ignored by media and scientists alike. We'll look at that next.