Molecular assembly indices of mineral heteropolyanions: some abiotic molecules are as complex as large biomolecules

Robert M Hazen; Peter C Burns; H James Cleaves 2nd; Robert T Downs; Sergey V Krivovichev; Michael L Wong

doi:10.1098/rsif.2023.0632

Molecular assembly indices of mineral heteropolyanions: some abiotic molecules are as complex as large biomolecules

J R Soc Interface. 2024 Feb;21(211):20230632. doi: 10.1098/rsif.2023.0632. Epub 2024 Feb 21.

Authors

Robert M Hazen¹, Peter C Burns^{2

3}, H James Cleaves 2nd^{1

4

5

6}, Robert T Downs⁷, Sergey V Krivovichev^{8

9}, Michael L Wong^{1

10}

Affiliations

¹ Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA.
² Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
³ Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
⁴ Earth Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan.
⁵ Blue Marble Space Institute for Science, Seattle, WA 98104, USA.
⁶ Department of Chemistry, Howard University, Washington, DC 20059, USA.
⁷ Geological Sciences, University of Arizona, Tucson, AZ 85721, USA.
⁸ Department of Crystallography, Institute of Earth Sciences, St. Petersburg State University, St. Petersburg 199034, Russia.
⁹ Nanomaterials Research Centre, Kola Science Centre, Russian Academy of Sciences, Fersmma 14, Apatity 184209, Russia.
¹⁰ Sagan Fellow, NASA Hubble Fellowship Program, Space Telescope Science Institute, Baltimore, MD 21218, USA.

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 H₂CO₃ 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.

Keywords: Titan; assembly theory; heteropolyanion; mineral evolution; molecular complexity.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Minerals* / chemistry
Molecular Conformation
Water*

Substances

Minerals
Water