• Mars had a surface environment that supported liquid water about 3.5 billion years ago, according to a study of river deposits spread across the red planet.
• A region of Mars named Aeolis Dorsa contains some of the most spectacular and densely packed river deposits seen on the planet, researchers said.
• These deposits are observable with satellite images because they have undergone a process called “topographic inversion,” where the deposits filling once topographically low river channels have been exhumed in such a way that they now exist as ridges at the surface of the planet, they said.
• With the use of high-resolution images and topographic data from cameras on orbiting satellites, researchers identified fluvial deposit stacking patterns and changes in sedimentation styles controlled by a migratory coastline.
• They also developed a method to measure river paleo-transport direction for a subset of these ridges.
• Together, these measurements demonstrate that the studied river deposits once filled incised valleys.
• On Earth, incised valleys are commonly cut and filled during falling and rising eustatic sea level, respectively.
• Cardenas and colleagues conclude that similar falling and rising water levels in a large water body forced the formation of the paleo-valleys in their study area.
• Cross-cutting relationships are observed at the valley-scale, indicating multiple episodes of water level fall and rise, each well over 50 metres, a similar scale to eustatic sea level changes on Earth, researchers said.
• The conclusion that such large water level fluctuations and coastline movements were recorded by these river deposits suggests some long-term stability in the controlling, downstream water body, which would not be expected from catastrophic hydrologic events.

Source:Science Daily