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Photos from a satellite orbiting Mars suggest the Red Planet was once a water-rich land of lakes, strengthening the theory that billions of years ago it had the conditions needed for the evolution of life. 

The photos, taken by the Mars Global Surveyor spacecraft, show massive sedimentary deposits, with thick layers of rock stacked one on top of another in miles-deep formations. 

“Some of the ... images of these outcrops show hundreds and hundreds of identically thick layers, which is almost impossible to have without water,” said Michael C. Malin, first author of a study being published Friday in the journal Science. 

Malin and his co-author, Kenneth S. Edgett, both researchers at Malin Space Sciences Systems in San Diego, said the photos show clear views of horizontal deposits of rock, a characteristic of sedimentary rock, in the walls of craters and chasms cut into the surface of Mars. 

Such layered rock structures are common on Earth where there were once lakes. Sediments can settle to the lake bottom and, over geologic time, form sheets of rock, one on top the other like pancakes in a stack. 

Malin and Edgett said such layered rock can be formed by wind or volcanic activity, but the prevalence of sedimentary outcrops on Mars suggests strongly the action of water. 

J. William Schopf, head of UCLA’s Center for the Study of Evolution and the Origin of Life, said the study gives strong support for theories that Mars billions of years ago was wetter, warmer and potentially more friendly to life. 

“This is the strongest evidence yet for what appear to be sedimentary units (rock formations) on Mars,” said Schopf. “If we saw these things from Earth orbit, we’d know” they were formed by water. 

Malin and Edgett suggested that craters, gouged out by asteroids, formed basins that collected water. With its many craters, Mars could have resembled a land of lakes. Sediment flowing into the craters could settle on the lake bottoms and eventually harden into layers of rock. 

They said the process occurred early in Mars’ history, between 4.3 billion and 3.5 billion years ago. 

If there once were lakes of water on the planet, Schopf said, “it makes it increasingly plausible” that life could have existed on Mars. He cautioned, however, that the only way to be sure is to go to Mars and return with samples. 

“You cannot have Earthlike life without having water, but the presence of water, in and of itself, doesn’t say that there was life there,” said Schopf. 

Many experts believe Mars may have been warmer and wetter billions of years ago and that some change in the planet’s atmosphere caused the open water to vaporize and disappear into space. Some have suggested Mars may still have subsurface pools of water, frozen there by the deep cold that now grips the planet. 

On the Net: NASA on the planets: http://pds.jpl.nasa.gov/planets/