Organic geochemical evidence for life in Archean rocks identified by pyrolysis–GC–MS and supervised machine learning
Abstract
Throughout Earth’s history, organic molecules from both abiogenic and biogenic sources have been buried in sedimentary rocks. Most of these organic molecules have been significantly altered by geologic processes through deep time. Nonetheless, the nature and distribution of those ancient fragmentary organic remains have the potential to reveal diagnostic biomolecular information after billions of years of burial. Here, we analyzed 406 fossil, modern biological, meteoritic, and synthetic samples using pyrolysis gas chromatography and mass spectrometry. We explored these analytical data via supervised machine-learning methods to discriminate samples of biogenic vs. abiogenic origin, plant vs. animal phylogenetic affinity, and photosynthetic vs. nonphotosynthetic physiology. Dividing 272 samples with known phylogenetic affinity and physiology into 9 categories, each further divided into 75% training and 25% testing sets, our random forest models accurately predict pairwise assignments of modern vs. fossil or meteoritic organics (100% correct assignments), fossil plant tissues vs. meteoritic organics (97%), modern vs. fossil plant tissues (98%), and modern plants vs. animal tissues (95%). Pairwise comparisons between fossil biogenic samples vs. abiogenic samples resulted in 93% correct classifications, while analysis of modern and ancient photosynthetic vs. nonphotosynthetic samples also resulted in 93% correct assignments. Our analyses demonstrate that molecular biosignatures can survive in ancient fossils and allow for the identification of organismal origins and traits. Consistent with previous morphological and isotopic inferences, we present evidence for biogenic molecular assemblages in Paleoarchean rocks (3.33 Ga) and for photoautotrophy in Neoarchean rocks (2.52 Ga).
Article Details
Journal Info
Proceedings of the National Academy of Sciences
National Academy of Sciences
Authors (29)
Michael L. Wong
Anirudh Prabhu
Earth and Planets Laboratory, Carnegie Institution for Science
Conel O’D. Alexander
Earth and Planets Laboratory, Carnegie Institution for Science
H. James Cleaves
Earth and Planets Laboratory, Carnegie Institution for Science
George D. Cody
Earth and Planets Laboratory, Carnegie Institution for Science
Grethe Hystad
Department of Mathematics and Statistics, Purdue University Northwest
Marko Bermanec
Department of Earth Sciences, University of Graz
Wouter Bleeker
Geological Survey of Canada
C. Kevin Boyce
Department of Geological Sciences, Stanford University
Andrea Corpolongo
Department of Geosciences, University of Cincinnati
Andrew D. Czaja
Department of Geosciences, University of Cincinnati
Souvik Das
State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits, Nanjing University
Robert R. Gaines
Geology Department, Pomona College
Daniel D. Gregory
Department of Earth Sciences, University of Toronto
John A. Jaszczak
A. E. Seaman Mineral Museum and Department of Physics, Michigan Technological University
Emmanuelle J. Javaux
Department of Geology, University of Liège
Jaganmoy Jodder
Department of Geosciences, University of Oslo
Andrew H. Knoll
Department of Organismic and Evolutionary Biology, Harvard University
Martin Van Kranendonk
School of Biological, Earth and Environmental Sciences, University of New South Wales
Katie M. Maloney
Department of Earth and Environmental Sciences, Michigan State University
Nora Noffke
Department of Ocean and Earth Sciences, Old Dominion University
Robert Rainbird
Geological Survey of Canada
Emersyn Slaughter
Department of Geological Sciences, University of Florida
Eva E. Stüeken
School of Earth and Environmental Sciences, University of St. Andrews
Roger E. Summons
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology
Frances Westall
Centre de Biophysique Moléculaire, CNRS-UPR4301
Jasmina Wiemann
Shuhai Xiao
Department of Geosciences, Virginia Tech
Robert M. Hazen
Earth and Planets Laboratory, Carnegie Institution for Science