Researchers David Shuster of the California Institute of Technology and Benjamin Weiss of the Massachusetts Institute of Technology, examined Martian meteorites called nakhlites and the famous ALH84001, which had been blasted from the surface of Mars to Earth. Shuster and Weiss measured the meteorites' loss of argon, which is highly dependent on temperature, in the minerals within the meteorites.
The results, reported in Science, showed that the meteorites could not have been heated to more than zero degrees celsius since the meteorites crystallised, estimated at four billion years ago. Therefore they concluded that the top several kilometres of the crust of Mars has not been significantly warmer during that period and so the surface of Mars probably has not had significant amounts of free-standing liquid water for the last 4 billion years.
Their finding does not mean that there were not pockets of isolated water in geothermal springs, but only that there have not been large areas of free-standing water for four billion years. Those surface features on Mars that indicate the presence and flow of liquid water must therefore have formed over relatively brief periods. This implies that it is unlikely that Mars has ever had an environment hospitable for life in the last 4 billion years, meaning that if Mars ever had life it would have had to be in the first half-billion years of its existence, when it was probably warmer.
I still consider it a real possibility that life originated on Mars, which may have been more favourable to life ~4.0 bya than the Earth. Being smaller than the Earth and nearer Jupiter, Mars may have been spared such an intense Late Heavy Bombardment 4.0-3.8 bya as the Earth. Life in the form of hardy single-celled bacteria , could then have been transferred from Mars via meteorite impact ejecta to Earth, which had then become more favourable for life, after the giant impact that created the Moon and the LHB, and then went extinct on Mars.
However, this then would make the fine-tuning problem of the Earth for life worse for evolution, in that not just one planet, Earth, but the Earth-Mars (and indeed the Earth-Moon, Mars and Jupiter) system would have to be just right in masses, orbits, time-frame, etc! If this was the case, then likelihood of life (let alone intelligent life) being on any other planet in the Universe, would have just become that much less!
 Whitehouse, D., "'Four-billion-year chill' on Mars," BBC, 21 July, 2005.
 Shuster, D.L. & Weiss, B.P., "Martian Surface Paleotemperatures from Thermochronology of Meteorites," Science, Vol 309, 22 July, 2005, pp.594-600.
 "Little liquid water on Mars for past 4 billion years: study," ABC, July 23, 2005.
 Britt, R.R., "Report: Mars Cold, Bitter Planet for a Long, Long Time," SPACE.com, 21 July, 2005.
 "Meteor study pours cold water on warm Mars theory," CNN/Reuters, July 22, 2005.
 This is questioned in Rana, F.R. & Ross, H.N., "Origins of Life: Biblical And Evolutionary Models Face Off," Navpress: Colorado Springs CO, 2004, p.194.
 Ward, P.D. & Brownlee, D.C., "The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World," , Piatkus: London, 2003, reprint, pp.72-73; Gonzalez G. & Richards J.W., "The Privileged Planet: How Our Place in the Cosmos is Designed For Discovery," Regnery: Washington DC, 2004, pp.39-40; Rana & Ross, 2004, p.195.