Molecular assembly indices of mineral heteropolyanions: some abiotic molecules are as complex as large biomolecules
Robert M. Hazen, Peter C. Burns, Henderson James Cleaves, Robert T. Downs, Sergey V. Krivovichev, Michael L. Wong
Abstract
Molecular assembly indices, which measure the number of unique sequential steps theoretically required to construct a three-dimensional molecule from its constituent atomic bonds, have been proposed as potential biosignatures. A central hypothesis of assembly theory is that any molecule with an assembly index ≥15 found in significant local concentrations represents an unambiguous sign of life. We show that abiotic molecule-like heteropolyanions, which assemble in aqueous solution as precursors to some mineral crystals, range in molecular assembly indices from 2 for H 2 CO 3 or Si(OH) 4 groups to as large as 21 for the most complex known molecule-like subunits in the rare minerals ewingite and ilmajokite. Therefore, values of molecular assembly indices ≥15 do not represent unambiguous biosignatures.