We've known since the 50's that the elements of life, simple amino acids , lipids can be formed by simulation of conditions similar to what was found in the early Earth. However, amino acids do not life make, before we get to life we need to have complex replicating chains of Amino Acids , called RNA ...and then we need protective shells for these RNA that are able to be permeated conditionally based on various interactions with materials outside of the membrane....in essence a primitive cell. Finding such entities on Mars would indicate that the process of building life is one that can form in the most inhospitable environments and should drastically increase the estimates for life in the Galaxy. Still it must be pointed out that life being able to form in extreme environments does not necessarily lead to life that can evolve to the complex form that we exist in, it could be that our form of life, introspective life is orders of magnitude more improbable to emerge from cell based life , leaving most of the galaxy one big petri dish of goo populated by the occasional macroscopic animal forms like ourselves only in rare occasions.
Still it is exciting to know that we are on the virge of finding out, it just may be that the results yield nothing interesting but that would not end the game, the solar system has several planetary bodies which have complex geothermal activity and chemistry that could be the seat of bizarre forms of life, such as the frozen moon of Saturn's Enceladus which is blessed with so much water it spews it into space in massive geysers that are now believed to be the source of one of Saturn's rings. Could Enceladus be spewing out more than just liquid to populate that ring? The preponderance of the materials that constitute living things in the solar system provides confidence that very interesting chemistries are being tried or have been tried and we know it happened at least once so it is possible that it could happen again.
Hopefully the experiments being conducted by Phoenix will answer that question definitively very soon.