Entrapment and protection of biosignatures by the jarosite group minerals

Since the discovery of jarosite on Mars, extensive research focuses on linking this mineral group with possible detection of biosignatures in the geologic record on Earth and Mars. The mineral jarosite can be generated abiotically or biotically. Because microbes can produce jarosite, it is possible that biomolecules could be trapped with the mineral. Multiple analytical methods, including extraction and mass spectrometry techniques, identify biomolecules in jarosite samples. Specifically, the amino acid glycine has been found associated with natural jarosite samples from various locations around the world. The simple amino acid may be merely physically mixed with the mineral. Alternatively, the biomolecule may be incorporated into the structure because jarosite is known as a "garbage" mineral because it easily incorporates substitutions. The jarosite end-members jarosite (sensu stricto-potassium jarosite), natrojarosite (sodium jarosite), and ammoniojarosite (ammonium jarosite) have potentially different susceptibilities to substitution as well as different thermodynamic stabilities and decomposition rates. Therefore, we have investigated whether a simple biomolecule, glycine, can be substituted into the structure of jarosite. If a biomolecule is entrapped within a mineral matrix, then it may be persist longer in the geologic record, even with exposure to the extreme conditions such as those on Mars. Glycine was introduced into the synthesis procedure of each jarosite end-member to elucidate the effects that glycine has on the stability of the mineral group and also determine if it produces a structural effect. Laser desorption/ionization Fourier transform mass spectrometry was used to determine that glycine was present with the jarosite after each synthesis. An understanding of the thermal and structural effects provides clues about whether the biomolecule is entrapped in the mineral, which may affect how persistent this bioorganic signature would be in the geologic record. Thermal gravimetric analysis was used to determine the effect that glycine has on the relationship between the thermodynamic stability of the end members and on the thermal decomposition behavior of each end member. X-ray and neutron diffraction have been used to investigate the structural relationship of glycine with each jarosite end member type. The results reveal distinct differences between jarosite that is merely physically mixed with glycine and jarosite that is synthesized in the presence of glycine for some end member groups. These differences suggest that glycine can be incorporated into the structure of jarosite. Therefore, it is possible that some biomolecules can be entrapped within a mineral matrix, which may be able to protect the biomolecules, allowing them to survive in the geologic record.