Identifying molecules as biosignatures with assembly theory and mass spectrometry

Geoffrey J T Cooper,Leroy Cronin,Emma Carrick,Graham Keenan,Heather Graham,Douglas G Moore,Stuart M Marshall,Piotr S Gromski,Matthew Craven,Sara I Walker,Cole Mathis

doi:10.1038/s41467-021-23258-x

Geoffrey J T Cooper, Leroy Cronin + Show 9 more

Open Access

https://doi.org/10.1038/s41467-021-23258-x

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Abstract

The search for alien life is hard because we do not know what signatures are unique to life. We show why complex molecules found in high abundance are universal biosignatures and demonstrate the first intrinsic experimentally tractable measure of molecular complexity, called the molecular assembly index (MA). To do this we calculate the complexity of several million molecules and validate that their complexity can be experimentally determined by mass spectrometry. This approach allows us to identify molecular biosignatures from a set of diverse samples from around the world, outer space, and the laboratory, demonstrating it is possible to build a life detection experiment based on MA that could be deployed to extraterrestrial locations, and used as a complexity scale to quantify constraints needed to direct prebiotically plausible processes in the laboratory. Such an approach is vital for finding life elsewhere in the universe or creating de-novo life in the lab.

Highlights

The search for alien life is hard because we do not know what signatures are unique to life
Our approach to life detection is based on the molecular assembly number (MA) which is derived from the theory of assembly pathways[7]
Since molecular assembly index (MA) is closely related to the structural heterogeneity of molecules, we developed a method based on tandem mass spectrometry (MS/MS)

Summary

Introduction

The search for alien life is hard because we do not know what signatures are unique to life. To do this we calculate the complexity of several million molecules and validate that their complexity can be experimentally determined by mass spectrometry This approach allows us to identify molecular biosignatures from a set of diverse samples from around the world, outer space, and the laboratory, demonstrating it is possible to build a life detection experiment based on MA that could be deployed to extraterrestrial locations, and used as a complexity scale to quantify constraints needed to direct prebiotically plausible processes in the laboratory. The problem with looking for such processes in a universal manner is the lack of a rigorous definition outside the context of known terrestrial biochemistry, and these cannot be deployed to design experiments This has led to several ambiguous results from ‘metabolic’ experiments done by the Viking Lander[1] on Mars, and investigations of potential meteorite ‘microfossils’[18]. 84001 meteorite, the criteria used to demarcate biogenic activity from abiogenic activity was not a quantitative measure, meaning the interpretation was always going to be ambiguous[19]

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