The measured abundance (30–50 ppb) of long-chain (C10–C12) alkanes and their possible carboxylic acid precursors found in the ancient Cumberland mudstone in Gale crater would have been substantially higher before the onset of exposure to ionizing radiation approximately 80 million years ago. Based on recent radiolysis experiments, we estimate conservatively that the Cumberland mudstone would have contained 120–7700 ppm of long-chain alkanes and/or fatty acids before ionizing radiation exposure. Such a high concentration of large organic molecules in martian sedimentary rocks cannot be readily explained by the accretion of organics from carbon-rich interplanetary dust particles and meteorites, nor by the deposition of hypothetical haze-derived organics from an ancient martian atmosphere. We discuss the feasibility of two additional mechanisms––one abiotic and one biological––that could have been capable of depositing this level of long-straight-chain organic molecules in the ancient martian mudstones: allochthonous transport of hydrothermally synthesized organics and autochthonous accumulation of organics from a hypothetical ancient Mars biosphere. To advance and test these and any additional working hypotheses put forth to explain such high concentrations of primary organics on Mars requires an understanding of the radiolytic degradation products expected for organics preserved in mineralogically comparable mudstones.
AponteJC, TarozoR, AlexandreMR, et al.Chirality of meteoritic free and IOM-derived monocarboxylic acids and implications for prebiotic organic synthesis. Geochim Cosmochim Acta, 2014; 131:1–12; doi: 10.1016/j.gca.2014.01.035
2.
BechtelA, SchubertCJ. A biogeochemical study of sediments from the eutrophic Lake Lugano and the oligotrophic Lake Brienz, Switzerland. Org Geochem, 2009; 40(10):1100–1114; doi: 10.1016/j.orggeochem.2009.06.009
3.
BennerSA, DevineKG, MatveevaLN, et al.The missing organic molecules on Mars. Proc Natl Acad Sci U S A, 2000; 97(6):2425–2430; doi: 10.1073/pnas.040539497
4.
BlandPA, SmithTB, JullAJT, et al.The flux of meteorites to the Earth over the last 50,000 years. Mon Not R Astron Soc, 1996; 283(2):551–565; doi: 10.1093/mnras/283.2.551
5.
BonnetJY, SzopaC, CosciaD, et al.Operations of the Sample Analysis at Mars instrument suite onboard the Curiosity rover. In: SpaceOps Conferences. SpaceOps; 2018; doi: 10.2514/6.2018-2372
6.
BristowTF, BishDL, VanimanDT, et al.The origin and implications of clay minerals from Yellowknife Bay, Gale Crater, Mars. Am Mineral, 2015; 100(4):824–836; doi: 10.2138/am-2015-5077CCBYNCND
7.
BristowTF, GrotzingerJP, RampeEB, et al.Brine driven diagenesis of clay minerals in Gale crater, Mars. Science, 2021; 373(6551):198–204; doi: 10.1126/science.abg5449
8.
BristowTF, HaberleRM, BlakeDF, et al.Low Hesperian PCO2 constrained from in situ mineralogical analysis at Gale Crater, Mars. Proc Natl Acad Sci U S A, 2017; 114(9):2166–2170; doi: 10.1073/pnas.1616649114
9.
ChassefièreE, LanglaisB, QuesnelY, et al.The fate of early Mars’ lost water: The role of serpentinization. JGR Planets, 2013; 118(5):1123–1134; doi: 10.1002/jgre.20089
10.
DartnellLR, DesorgherL, WardJM, et al.Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology. Geophys Res Lett, 2007; 34(2); doi: 10.1029/2006GL027494
11.
EigenbrodeJL, SummonsRE, SteeleA, et al.Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars. Science, 2018; 360(6393):1096–1101; doi: 10.1126/science.aas9185
12.
FarleyKA, MalespinC, MahaffyP, et al.; MSL Science Team. In situ radiometric and exposure age dating of the Martian surface. Science, 2014; 343(6169):1247166; doi: 10.1126/science.1247166
13.
FlynnGJ. Atmospheric entry heating: A criterion to distinguish between asteroidal and cometary sources of interplanetary dust. Icarus, 1989; 77(2):287–310; doi: 10.1016/0019-1035(89)90091-2
14.
FlynnGJ. The delivery of organic matter from asteroids and comets to the early surface of Mars. Earth Moon Planets, 1996; 72:469–474; doi: 10.1007/BF00117551
15.
FlynnGJ, McKayDS. An assessment of the meteoritic contribution to the Martian soil. J Geophys Res, 1990; 95(B9):14497–14509; doi: 10.1029/JB095iB09p14497
16.
FreissinetC, GlavinDP, ArcherPD, et al.Long-chain alkanes preserved in a martian mudstone. Proc Natl Acad Sci U S A, 2025; 122(13):e2420580122; doi: 10.1073/pnas.2420580122
17.
FreissinetC, KnudsonCA, GrahamHV, et al.Benzoic acid as the preferred precursor for the chlorobenzene detected on Mars: Insights from the unique Cumberland analog investigation. Planet Sci J, 2020; 1(2):41; doi: 10.3847/PSJ/aba690
18.
FrenchKL, HallmannC, HopeJM, et al.Reappraisal of hydrocarbon biomarkers in Archean rocks. Proc Natl Acad Sci U S A, 2015; 112(19):5915–5920; doi: 10.1073/pnas.1419563112
19.
GlavinDP, AlexanderC, AponteJC, et al.The origin and evolution of organic matter in carbonaceous chondrites and links to their parent bodies. In Primitive Meteorites and Asteroids. (AbreuN, ed.) Elsevier: Amsterdam; 2018; pp 205–271.
20.
GlavinDP, DworkinJP, AlexanderCMO, et al.Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu. Nat Astron, 2025; 9(2):199–210; doi: 10.1038/s41550-024-02472-9
21.
GlavinDP, FreissinetC, MillerKE, et al.Evidence for perchlorates and the origin of chlorinated hydrocarbons detected by SAM at the Rocknest aeolian deposit in Gale Crater. JGR Planets, 2013; 118(10):1955–1973; doi: 10.1002/jgre.20144
22.
GradyMM, VerchovskyAB, WrightIP. Magmatic carbon in martian meteorites: Attempts to constrain the carbon cycle on Mars. Int J Astrobiol, 2004; 3(2):117–124; doi: 10.1017/S1473550404002071
23.
HallidayI, GriffinAA, BlackwellAT. Detailed data for 259 fireballs from the Canadian camera network and inferences concerning the influx of large meteoroids. Meteorit & Planetary Scien, 1996; 31(2):185–217; doi: 10.1111/j.1945-5100.1996.tb02014.x
24.
HaoJ, KnollAH, HuangF, et al.Cycling phosphorus on the Archean Earth: Part II. Phosphorus limitation on primary production in Archean ecosystems. Geochim Cosmochim Acta, 2020; 280:360–377; doi: 10.1016/j.gca.2020.04.005
25.
HasslerDM, ZeitlinC, Wimmer-SchweingruberRF, et al.; MSL Science Team. Mars’ surface radiation environment measured with the Mars Science Laboratory’s Curiosity rover. Science, 2014; 343(6169):1244797; doi: 10.1126/science.1244797
26.
HeD, WangX, YangY, et al.Hydrothermal synthesis of long-chain hydrocarbons up to C24 with NaHCO3-assisted stabilizing cobalt. Proc Natl Acad Sci U S A, 2021; 118(51):e2115059118; doi: 10.1073/pnas.2115059118
27.
HuangY, WangY, AlexandreMR, et al.Molecular and compound-specific isotopic characterization of monocarboxylic acids in carbonaceous meteorites. Geochim Cosmochim Acta, 2005; 69(4):1073–1084; doi: 10.1016/j.gca.2004.07.030
28.
HurowitzJA, TiceMM, AllwoodAC, et al.Redox-driven mineral and organic associations in Jezero crater, Mars. Nature, 2025; 645(8080):332–340; doi: 10.1038/s41586-025-09413-0
29.
KharechaP, KastingJ, SiefertJ. A coupled atmosphere–ecosystem model of the early Archean Earth. Geobiology, 2005; 3(2):53–76; doi: 10.1111/j.1472-4669.2005.00049.x
30.
KiteES, MischnaMA, GaoP, et al.Methane release on early Mars by atmospheric collapse and atmospheric reinflation. Planet Space Sci, 2020; 181:104820; doi: 10.1016/j.pss.2019.104820
31.
KminekG, BadaJ. The effect of ionizing radiation on the preservation of amino acids on Mars. Earth Planet Sci Lett, 2006; 245(1–2):1–5; doi: 10.1016/j.epsl.2006.03.008
32.
LewisJM, BowerDM, PavlovAA, et al.Organic products of fatty acid and magnesium sulfate mixtures after gamma radiolysis: Implications for missions to Europa. Astrobiology, 2024; 24(12):1166–1186; doi: 10.1089/ast.2024.0047
33.
LotemN, RasmussenB, ZiJW, et al.Reconciling Archean organic-rich mudrocks with low primary productivity before the Great Oxygenation Event. Proc Natl Acad Sci U S A, 2025; 122(2):e2417673121; doi: 10.1073/pnas.2417673121
34.
LoveSG, BrownleeDE. A direct measurement of the terrestrial mass accretion rate of cosmic dust. Science, 1993; 262(5133):550–553; doi: 10.1126/science.262.5133.550
35.
MahaffyP, WebsterCR, CabaneM, et al.The Sample Analysis at Mars investigation and instrument suite. Space Sci Rev, 2012; 170(1–4):401–478; doi: 10.1007/s11214-012-9879-z
36.
McCollomTM, RitterG, SimoneitBRT. Lipid synthesis under hydrothermal conditions by Fischer–Tropsch-type reactions. Orig Life Evol Biosph, 1999; 29(2):153–166; doi: 10.1023/A:1006592502746
37.
MillanM, WilliamsAJ, McAdamAC, et al.Sedimentary organics in Glen Torridon, Gale crater, Mars: Results from the SAM instrument suite and supporting laboratory analyses. JGR Planets, 2022; 127(11):e2021JE007107; doi: 10.1029/2021JE007107
38.
NaraokaH, TakanoY, DworkinJP, et al.Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu. Science, 2023; 379(6634):eabn9033; doi: 10.1126/science.abn9033
39.
PavlovAA, BrownLL, KastingJF. UV shielding of NH3 and O2 by organic hazes in the Archean atmosphere. J Geophys Res, 2001b;106(E10):23267–23287; doi: 10.1029/2000JE001448
40.
PavlovAA, KastingJF, BrownLL, et al.Greenhouse warming by CH4 in the atmosphere of early Earth. J Geophys Res, 2000; 105(E5):11981–11990; doi: 10.1029/1999JE001134
41.
PavlovAA, KastingJF, EigenbrodeJL, et al.Organic haze in Earth’s early atmosphere: Source of low-13C Late Archean kerogens? Geol, 2001a;29(11):1003–1006; doi: 10.1130/0091-7613(2001)029<1003:OHIESE>2.0.CO;2
42.
PavlovAA, McLainHL, FarnsworthKK, et al.Slow radiolysis of amino acids in Mars-like permafrost conditions: Applications to the search for extant life on Mars. Astrobiology, 2025; 25(9):601–610; doi: 10.1177/15311074251366249
43.
PavlovAA, McLainHL, GlavinDP, et al.Radiolytic effects on biological and abiotic amino acids in shallow subsurface ices on Europa and Enceladus. Astrobiology, 2024; 24(7):698–709; doi: 10.1089/ast.2023.0120
44.
PavlovAA, McLainHL, GlavinDP, et al.Rapid radiolytic degradation of amino acids in the martian shallow subsurface: Implications for the search for extinct life. Astrobiology, 2022; 22(9):1099–1115; doi: 10.1089/ast.2021.0166
45.
PavlovAA, VasilyevG, OstryakovVM, et al.Degradation of the organic molecules in the shallow subsurface of Mars due to irradiation by cosmic rays. Geophys Res Lett, 2012; 39(13):L13202; doi: 10.1029/2012GL052166
46.
PurvisG, ŠillerL, CrosskeyA, et al.Generation of long-chain fatty acids by hydrogen-driven bicarbonate reduction in ancient alkaline hydrothermal vents. Commun Earth Environ, 2024; 5(1):30; doi: 10.1038/s43247-023-01196-4
47.
RobinsonN, EglintonG, CranwellPA, et al.Messel oil shale (western Germany): Assessment of depositional palaeoenvironment from the content of biological marker compounds. Chem Geol, 1989; 76(1–2):153–173; doi: 10.1016/0009-2541(89)90134-4
48.
RousselA, McAdamAC, GrahamHV, et al.Diagnostic biosignature transformation under simulated Martian radiation in organic-rich sedimentary rocks. Front Astron Space Sci, 2022; 9:919828; doi: 10.3389/fspas.2022.919828
49.
RousselA, McAdamAC, PavlovAA, et al.Variable and large losses of diagnostic biomarkers after simulated cosmic radiation exposure in clay- and carbonate-rich Mars analog samples. Astrobiology, 2024a;24(7):669–683; doi: 10.1089/ast.2023.0123
50.
RousselA, PavlovAA, DworkinJP, et al.Rapid destruction of lipid biomarkers under simulated cosmic radiation. Astrobiology, 2024b;24(11):1063–1073; doi: 10.1089/ast.2024.0006
51.
RushdiAI, SimoneitBRT. Lipid formation by aqueous Fischer–Tropsch-type synthesis over a temperature range of 100 to 400 °C. Orig Life Evol Biosph, 2001; 31(1–2):103–118; doi: 10.1023/a:1006702503954
52.
SaganC. Broca’s Brain: Reflections on the Romance of Science. Hodder and Stoughton: London; 1979.
53.
SmithDJ, EglintonG, MorrisRJ. The lipid chemistry of an interfacial sediment from the Peru continental shelf: Fatty acids, alcohols, aliphatic ketones and hydrocarbons. Geochim Cosmochim Acta, 1983; 47(12):2225–2232; doi: 10.1016/0016-7037(83)90045-5
54.
SteeleA, BenningLG, WirthR, et al.Organic synthesis on Mars by electrochemical reduction of CO2. Sci Adv, 2018; 4(10):eaat5118; doi: 10.1126/sciadv.aat5118
55.
SteeleA, McCubbinFM, FriesM, et al.A reduced organic carbon component in martian basalts. Science, 2012; 337(6091):212–215; doi: 10.1126/science.1220715
56.
SternJC, MalespinCA, EigenbrodeJL, et al.Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars. Proc Natl Acad Sci U S A, 2022; 119(27):e2201139119; doi: 10.1073/pnas.2201139119
57.
SummonsRE, PowellTG, BorehamCJ. Petroleum geology and geochemistry of the Middle Proterozoic McArthur Basin, Northern Australia: III. Composition of extractable hydrocarbons. Geochim Cosmochim Acta, 1988; 52(7):1747–1763; doi: 10.1016/0016-7037(88)90001-4
58.
SunMY, WakehamSG. Molecular evidence for degradation and preservation of organic matter in the anoxic Black Sea Basin. Geochim Cosmochim Acta, 1994; 58(16):3395–3406; doi: 10.1016/0016-7037(94)90094-9
59.
SutterB, ArcherPDJr, MingDW, et al.Evolved gas analyses of sedimentary rocks and eolian sediment in Gale Crater, Mars: Results of the Curiosity rover’s Sample Analysis at Mars instrument from Yellowknife Bay to the Namib Dune. JGR Planets, 2017; 122(12):2574–2609; doi: 10.1002/2016JE005225
60.
SzopaC, FreissinetC, BuchA, et al.First detections of dichlorobenzene isomers and trichloromethylpropane from organic matter indigenous to Mars mudstone in Gale Crater, Mars: Results from the Sample Analysis at Mars instrument onboard the Curiosity rover. Astrobiology, 2020; 20(2):292–306; doi: 10.1089/ast.2018.1908
61.
TrainerMG, PavlovAA, DeWittHL, et al.Organic haze on Titan and the early Earth. Proc Natl Acad Sci U S A, 2006; 103(48):18035–18042; doi: 10.1073/pnas.0608561103
62.
VanBommelSJ, GellertR, BergerJA, et al.Mars science laboratory alpha particle X-ray spectrometer trace elements: Situational sensitivity to Co, Ni, Cu, Zn, Ga, Ge, and Br. Acta Astronaut, 2019; 165:32–42; doi: 10.1016/j.actaastro.2019.08.026
63.
VanimanDT, BishDL, MingDW, et al.; MSL Science Team. Mineralogy of a mudstone at Yellowknife Bay, Gale crater, Mars. Science, 2014; 343(6169):1243480; doi: 10.1126/science.1243480
64.
WardLM, RasmussenB, FischerWW. Primary productivity was limited by electron donors prior to the advent of oxygenic photosynthesis. JGR Biogeosciences, 2019; 124(2):211–226; doi: 10.1029/2018JG004679
65.
WilliamsAJ, EigenbrodeJL, SummonsRE, et al.Recovery of fatty acids from mineralogic Mars analogs by TMAH thermochemolysis for the Sample Analysis at Mars wet chemistry experiment on the Curiosity rover. Astrobiology, 2019; 19(4):522–546; doi: 10.1089/ast.2018.1819
66.
WordsworthR, KaluginaY, LokshtanovS, et al.Transient reducing greenhouse warming on early Mars. Geophys Res Lett, 2017; 44(2):665–671; doi: 10.1002/2016GL071766
67.
ZahnleKJ. Photochemistry of methane and the formation of hydrocyanic acid (HCN) in the Earth’s early atmosphere. J Geophys Res, 1986; 91(D2):2819–2834; doi: 10.1029/JD091iD02p02819
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
