To understand just why Mars currently has no life forms, we need to look at how the planet has evolved, and what conditions deteriorated or developed, that made life unsupportable.
As far back as 1890, before airplanes took flight, let alone space missions, a Danish scientist had concluded that the sun would not be able to keep the surface temperature of Mars, above -37 centigrade, or -34F. He had already grasped one of the primary reasons Mars could not be inhabited.
This was argued vociferously by American astronomy enthusiast Percival Lowell, who conducted a year-long observation project of Mars, from a location in Arizona. His work suggested that Mars was earth-like, with a harsh atmosphere in which nitrogen, the most abundant gas on Earth (and essential for life) was present in abundance. Therefore, while there may not presently be intelligent life, Mars was capable of supporting it. However, the Mariner 4 mission in 1965, would cut the underpinnings from his work when it brought the first essential information on the Martian atmosphere: it was thin, not nearly as dense as Earth’s, contained mostly carbon dioxide, and showed no evidence at all of nitrogen on spectroscopic examination.
Initially thought to be a dead, moon-like planet, further Mariner missions brought the surprising revelation, that there appeared to be canals and channels, that hinted at the past existence of large quantities of moving, liquid water.
Edward Anders’ article in the November 1977 issue of Science, noted that smaller planets such as Mars, the Moon and Mercury, are poorer in volatiles, due to their small size, and suffer greater loss of light gases, as well as incomplete outgassing.
The atmosphere, once calculated to be 10-25% that of Earth, because of its nitrogen content, was now found to be nowhere near that figure, with nitrogen making up only 2% of the atmosphere, compared to the terrestrial level of 77%. It was thought that perhaps the relatively low level of volcanic activity, compared to Earth, resulted in less release of nitrogen, and that the weak gravity resulted in the loss of most of it. Unable to actually dig around on the surface and utilize modern dating methods, scientists have declared an incredibly broad range of dates for the birth of the youngest of Mars’ volcanoes, Olympus Mons, ranging from a couple hundred million years to 2.5 billion.
It follows then, that scientists are unable to accurately trace the timeline for evolution or development of the planet. Erosion features that suggest flowing water or runoffs, must have resulted from bodies of water that were part of the planet’s first “few” million years, along with a denser atmosphere. Over time, the CO2 content would have turned into carbonates on the bottom of the lakes, lowering the temperature until their water froze. The only way to have avoided this scenario, would have been for Mars to have a natural recycling process. But the only one present, volcanic activity, was not sufficient to throw back into the atmosphere, the CO2 needed to maintain the temperature. When that activity ceased, the thermometer dropped, aided possibly by pockets of underground water. So that in the end, the life sustaining substance, contributed to the inhospitable cold, making life insupportable.