In chemistry 101 and 102 even at the High School level, one is introduced to the Chart of Elements. We learn about electrons, protons, neutrons and all those orbital shells.
Organic life, is based upon Carbon, Nitrogen, Oxygen, Helium, Phosphorous and a smigging of the other elements. It is what makes DNA and RNA nucleotide bases.
Alien life, could include Silicon, as a replacement for the Carbon.
and or the nucleotide bases? If "Alien life" exists even a secondary and unique evolution of life on Mars, then how could the DNA or nucleotide bases have unique variations to actually be deemed "Alien life"? One cannot take a mouse an...d expect it to radically change the DNA and nucleotide sequences to find out if it would be an alien life form.
However, a terrestial microbe could be coaxed into possible modifications given limiting factors, i.e., replacement of the Phosphorus with arsenic to see if it survives--and in the collection of this microbe that currently exist in an area where high concentrations of arsenic exist. Then what is causing it to exist naturally within the environment? There isn't a perilous contention in allow the microbe to exist and observe multi-generations in a more harsh environment surrounded by arsenic. The microbe and the descending populations over time show evolution occurring, at a basic level. Darwinian Finch's and the changes from an initial founding population.