**3. Intriguing sedimentary microstructures, chemicals and complex organics found by Curiosity rover at Gale Crater**

At Pahrump Hill (Mojave and Mojave 2 targets, at Sols 809 and 880) a large number of light-toned lozenge-shaped pervasive microstructures having dimensions and shape comparable to rice grains (nicknamed here as "rice grain") were found and regarded by NASA as pseudomorphic sulfate crystals resulting from occasional lake evaporation [7]. In this location, Curiosity detected mineral assemblage suggest, paradoxically, both oxidizing (hematite) and reducing (magnetite) environments, as well as acidic (diagenetic and/or authigenic jarosite) and neutral (apatite) conditions; findings difficult to explain as having an abiological origin and more compatible with a biological origin.

In this work we hypothesize that among the structures imaged by Curiosity at Mojave targets some are suggestive of bacterially mediated reactions or are the remnants of fossilized life forms, and which also agrees with the organic molecules detected just on such target (**Table 1**).

Hence, the objective of this study was to investigate the microstructures observed at Sols 809 and 880 (Mojave and Mojave 2 targets; the same site on successive paths) in order to determine their possible biogenicity. These structures were described by NASA as lozenge shaped, pseudomorphic minerals (https://www.nasa.gov./jpl/msl/pia19077).

First, we studied the morphology of microstructures with reference to possible parallels with primitive terrestrial forms of life, such as stromatolites/microbialites, microfossils and/or algae, taking in account previous similar possible finds observed by Martian rovers. Parallels emerged by a systematic image analysis, considering terrestrial similar forms and sedimentary processes, both syn-genetic and postgenetic, in a given environment.

Second, we morphometrically analyzed the lozenge-shaped structures, here called "rice grains" (**Figure 2**), observed at the same targets, in order to investigate if their microstructures are compatible to sulphate crystals (Gypsum, Jarosite) as well to other minerals contained in these outcroppings or to primitive terrestrial forms of life.
