Mars lost most of its atmosphere over time, leaving an extremely arid and cold desert similar to Antarctica. "That's not to say that no life can occur under those conditions," Tosca said. "But there were times when it was friendlier." Life on Earth is believed to have begun about 3.5 billion years ago. The planet's salt-loving micro-organisms actually evolved from ancestors that didn't do so well in briny water, said Tosca, who works with a team at Harvard studying the origin of life on Earth. "The starting point for life on Earth was easier than on Mars," Tosca said. Because liquid water is required by all living organisms on Earth, its presence is believed to be a prerequisite for life elsewhere. "Further evaluation of habitability, however, requires that we move beyond the mere presence of water to consider its properties," the researchers wrote. Not all waters are habitable, they added. The limits of terrestrial life are defined by additional parameters, including temperature, pH and salinity. "From what we know about the origins of life on Earth, an acid pH and high salinity might not have worked so well for the evolution of life on Mars," Tosca said. Related Links: Irene Klotz's blog: Free Space How Stuff Works: Mars Phoenix Lander |
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