So, as long as water existed, microscopic life could have thrived on the planet and died out as Mars froze and lost most of its atmosphere. But maybe the bacteria didn't die. Organisms adaptable Scientists believe living creatures could exist today if they retreated to remaining pockets of liquid in the warmer interior of the planet. This notion has gained credence as scientists discover such examples on Earth, where living things are surviving under the most hostile conditions imaginable. They include bacteria inside scalding volcanoes, in the boiling deep-sea vents on the ocean floor, buried in the Earth's unforgiving crust and amid the frozen deserts of Antarctica.
Some microbes can survive without oxygen, using chemicals instead of sunlight for energy.
Based on what I've seen, there's no way to rule out the possibility of life on Mars. I don't have any doubt that if there were Martian organisms on Mars long ago, they certainly would have the ability to adapt to the planet's present environment. One such spot could be the Martian highlands, where water might have pooled for eons. But to search for present life, scientists would have to pinpoint likely locations for water deep inside Mars - and then dig. In either case, finding evidence will be very difficult.