Life
  Definition of Life
  Fossils
  Martian Meteorite

Data Analysis
  Thin Section Analysis
  Isotope Analysis
  Gas Chromatograph Mass Spectrometer
  Infrared Spectroscopy
  Alpha-Proton X-Ray Spectrometer
  Detection of Carbon Complexes
  Labeled Release
  Gas Exchange
  Pyrolytic Release
  Stimulus Response Experiments
 

One simple way to test of the presence of life would be to test the soil for molecules that are by-products of life. An abiotic sample would contain a normal distribution of molecule types, while a biotic sample would have spikes for certain molecules. This would be an easy experiment to do with a gas chromatography mass spectrometer (GCMS). For further information about how GCMS works, click here. One would not need the organism, just the soil, to show that biological activity exists. This instrument is capable of detecting trace amounts of various organic and inorganic compounds. Water will be a key molecular compound that will suggest the possibility of life. 

Positive: Greater amounts of some organic molecules such as amino acids in a sample than others. Earth soil might be a good comparison to show the sort of distribution that one can expect on a planet filled with life. Even if a non-random distribution of organic molecules were found on Mars, they would probably not be as prevalent as on Earth.

Negative: A smooth distribution of these organic molecules as found most elsewhere in the universe. A moon rock is a good comparison. 

False-Positive: In the case of a positive response, we would have to examine any possible inorganic methods for the creation of these molecules. Then we would look for a situation or event on Mars that would allow this to happen.