|Above: A comparison of the 'micro-digitate' structures, on Earth and Mars. Courtesy of NASA.|
An interesting theory has been put forward in a paper presented, at the 2015 AGU fall meeting. Titled " Micro-digitate Silica Structures on Earth and Mars: Potential Biosignatures Revealed in the Geyser Field of El Tatio, Chile", the gist of it is this: Certain types of volcanic spring produce deposits of silica round their edges. Those deposits can take on these strange 'micro digitate' structures, for no really obvious reason - and the paper has an explanation that could lead us to evidence of bacterial life on Mars: The 'digitate' structures are due to the action of bacteria, growing in the forming deposits.
If these weird looking structures did form through microbial action it would be big news for the search for Martian life, because the extinct 'home plate' geothermal spring which was surveyed by the Spirit Mars rover. The abstract is here, and Universe today has done a nice in-detailed breakdown of the theory here.