Scientists Study 226 Ancient Lakes on Red Planet Surface

The mud and clays ideal for preserving fossil records are less common around Martian lakes than on Earth.
A team of scientists from Brown University pored over surface images from the Mars Reconnaissance Orbiter, the Mars Odyssey Spacecraft, and the Mars Express spacecraft in search of lakes that once boasted water rushing out as well as in. They then analyzed the reflected light from each lake to determine their chemical composition, hoping to identify the muds and clays found in such systems on Earth. They found that only 79 of the beds contained deposits of minerals that hint at clays on the surface. As said scientists this scarcity could be a result of the chemistry of mixing Martian water and the surrounding land, or it could be another sign that water on the Red Planet only stuck around for a brief period of time. If life evolved on Mars, deposits of clay and sediment could contain evidence of its existence. Water rushing over mineral grains stirs and mixes them, chemically altering their structure as it moves along. But if the water only flowed briefly for a given lake, there may not have been time for the creation of large quantities of clay. According to the team, all of the examined lakes have undergone some form of resurfacing since they became inactive more than 3.7 billion years ago. Lava flowing from volcanoes covered some of the beds, and icy glaciers crept down from the poles to hide others. In some cases, weathering eroded these new layers, exposing the clay sediments. The Nili Fossae region, circled, contains an unusually high density of sedimentary deposits, likely caused by the large degree of erosion in the area. So when Curiosity rover lands on Mars this summer, it will search clays and sediments in the Gale Crater for indications of past environments that could have supported microbial life.
source:www.space.com