Previous spacecraft investigations have pointed to the possible presence of an ancient ocean, with supporters for the idea that there is still a substantial amount of water under the surface as liquid or ice. Climate change over millions of years might have led to the disappearance of the atmosphere, which would mean that any water on the surface would boil away.
Volcanic activity is among other explanations for apparent gullies, river valleys, flood plains, lakes, seas and other signs of water that have vanished.
Gaetano Di Achille and Bryan Hynek, of the University of Colorado, led a team that analysed the distribution of supposed ancient delta deposits and river-valley networks on Mars. They found many of the deltas were at a similar elevation and suggested these might ring an ancient shoreline, providing strong support for a vast ocean once covering the northern plains of the planet.
If there was that much liquid water, there had to be life. When will we start finding real Martians?
iBiome 
I wonder when Mars may have “lost” it’s water. Textbooks, fifth grade teachers, and even a recent Economist talk about the hydrological cycle of water – and particularly evapotranspiration – but never, ever about how water is naturally created nor where it comes from. Thank you, Internet, for informing me that it mostly comes from outer space. Questions: Were Mars and Earth created around the same time frame; if so, did they collect roughly the same amount of water from space during early formation (granted Mars being smaller/less dense); assuming Mars had surface water at some point, did it’s water seep underground or was it exhausted into space? Or both. What “event” would cause Mars to loose its water? If that “event” was the loss of a dense or heavy enough atmosphere, what caused that loss? Is it possible that Mars’ water siphoned off over to Earth (getting back to the timeline question above)? Just a few questions that never seem to get answered by teachers, textbooks, or nasa …
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