Demosponge steroid biomarker 26-methylstigmastane provides evidence for Neoproterozoic animals

Zumberge, J. Alex; Love, Gordon D.; Cárdenas, Paco; Sperling, Erik A.; Gunasekera, Sunithi; Rohrssen, Megan; Grosjean, Emmanuelle; Grotzinger, J. P.; Summons, Roger E.

doi:10.1038/s41559-018-0676-2

Cited by 93 publications

(84 citation statements)

References 38 publications

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“…Contamination is a primary concern—from migration of hydrocarbons across a billion or more years of burial history or from oil‐based additives used to drill the cores (Grosjean & Logan, ). Fortunately, we can screen for this possibility through meticulous methodology designed to identify and prevent contamination (Brocks, ; Brocks et al., ; Flannery & George, ; French et al., ; Love et al., ; Luo, Hallmann, Xie, Ruan, & Summons, ; Pawlowska, Butterfield, & Brocks, ; Zumberge et al., ).…”

Section: Resultsmentioning

confidence: 99%

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

et al. 2019

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By about 2.0 billion years ago (Ga), there is evidence for a period best known for its extended, apparent geochemical stability expressed famously in the carbonate–carbon isotope data. Despite the first appearance and early innovation among eukaryotic organisms, this period is also known for a rarity of eukaryotic fossils and an absence of organic biomarker fingerprints for those organisms, suggesting low diversity and relatively small populations compared to the Neoproterozoic era. Nevertheless, the search for diagnostic biomarkers has not been performed with guidance from paleoenvironmental redox constrains from inorganic geochemistry that should reveal the facies that were most likely hospitable to these organisms. Siltstones and shales obtained from drill core of the ca. 1.3–1.4 Ga Roper Group from the McArthur Basin of northern Australia provide one of our best windows into the mid‐Proterozoic redox landscape. The group is well dated and minimally metamorphosed (of oil window maturity), and previous geochemical data suggest a relatively strong connection to the open ocean compared to other mid‐Proterozoic records. Here, we present one of the first integrated investigations of Mesoproterozoic biomarker records performed in parallel with established inorganic redox proxy indicators. Results reveal a temporally variable paleoredox structure through the Velkerri Formation as gauged from iron mineral speciation and trace‐metal geochemistry, vacillating between oxic and anoxic. Our combined lipid biomarker and inorganic geochemical records indicate at least episodic euxinic conditions sustained predominantly below the photic zone during the deposition of organic‐rich shales found in the middle Velkerri Formation. The most striking result is an absence of eukaryotic steranes (4‐desmethylsteranes) and only traces of gammacerane in some samples—despite our search across oxic, as well as anoxic, facies that should favor eukaryotic habitability and in low maturity rocks that allow the preservation of biomarker alkanes. The dearth of Mesoproterozoic eukaryotic sterane biomarkers, even within the more oxic facies, is somewhat surprising but suggests that controls such as the long‐term nutrient balance and other environmental factors may have throttled the abundances and diversity of early eukaryotic life relative to bacteria within marine microbial communities. Given that molecular clocks predict that sterol synthesis evolved early in eukaryotic history, and (bacterial) fossil steroids have been found previously in 1.64 Ga rocks, then a very low environmental abundance of eukaryotes relative to bacteria is our preferred explanation for the lack of regular steranes and only traces of gammacerane in a few samples. It is also possible that early eukaryotes adapted to Mesoproterozoic marine environments did not make abundant steroid lipids or tetrahymanol in their cell membranes.

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Section: Resultsmentioning

confidence: 99%

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

et al. 2019

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“…The possible causal relationship between oxygenation events and early animal evolution is a topic of broad interest. Molecular clock and sponge biomarker studies suggest that multicellular animals diverged in the Cryogenian Period (~720–635 Myr ago) or earlier (Cunningham et al, ; Sperling and Stockey, ; Zumberge et al, , but see Nettersheim et al, ). However, Cryogenian animals may have been morphologically simple sponge‐like creatures and likely required little oxygen (Mills, Lenton, & Watson, ; Sperling et al, ).…”

Section: Global Marine Redox Change Drove the Rise And Fall Of The Edmentioning

confidence: 99%

Global marine redox changes drove the rise and fall of the Ediacara biota

et al. 2019

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The role of O2 in the evolution of early animals, as represented by some members of the Ediacara biota, has been heavily debated because current geochemical evidence paints a conflicting picture regarding global marine O2 levels during key intervals of the rise and fall of the Ediacara biota. Fossil evidence indicates that the diversification the Ediacara biota occurred during or shortly after the Ediacaran Shuram negative C‐isotope Excursion (SE), which is often interpreted to reflect ocean oxygenation. However, there is conflicting evidence regarding ocean oxygen levels during the SE and the middle Ediacaran Period. To help resolve this debate, we examined U isotope variations (δ238U) in three carbonate sections from South China, Siberia, and USA that record the SE. The δ238U data from all three sections are in excellent agreement and reveal the largest positive shift in δ238U ever reported in the geologic record (from ~ −0.74‰ to ~ −0.26‰). Quantitative modeling of these data suggests that the global ocean switched from a largely anoxic state (26%–100% of the seafloor overlain by anoxic waters) to near‐modern levels of ocean oxygenation during the SE. This episode of ocean oxygenation is broadly coincident with the rise of the Ediacara biota. Following this initial radiation, the Ediacara biota persisted until the terminal Ediacaran period, when recently published U isotope data indicate a return to more widespread ocean anoxia. Taken together, it appears that global marine redox changes drove the rise and fall of the Ediacara biota.

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“…The origin and diversification of complex life on Earth is fundamentally tied to the rise of oxygen (O 2 ) in our atmosphere and oceans (Lyons et al 2014;Planavsky et al 2014;Reinhard et al 2016). Physical and geochemical evidence for eukaryotes (complex cells with organelles, such as mitochondria and chloroplasts) is absent from the rock record until well after the earliest accumulation of free O 2 in Earth's atmosphere ∼2.3 billion years ago (Ga) (Knoll 2014;Luo et al 2016), while the first metazoan (animal) life emerged only in the last ∼700 million years (Erwin et al 2011;Zumberge et al 2018). Later, significant increases in biological complexity on Earth, such as the Cambrian Explosion (∼542 Ma; Lee et al 2013), occurred against the backdrop of a more strongly oxygenated planetary atmosphere.…”

Section: Requirements Of Complex Life and Co 2 Levels In The Hzmentioning

confidence: 99%

A Limited Habitable Zone for Complex Life

Schwieterman

Reinhard

Olson

et al. 2019

ApJ

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The habitable zone (HZ) is commonly defined as the range of distances from a host star within which liquid water, a key requirement for life, may exist on a planet's surface. Substantially more CO 2 than present in Earth's modern atmosphere is required to maintain clement temperatures for most of the HZ, with several bars required at the outer edge. However, most complex aerobic life on Earth is limited by CO 2 concentrations of just fractions of a bar. At the same time, most exoplanets in the traditional HZ reside in proximity to M dwarfs, which are more numerous than Sun-like G dwarfs but are predicted to promote greater abundances of gases that can be toxic in the atmospheres of orbiting planets, such as carbon monoxide (CO). Here we show that the HZ for complex aerobic life is likely limited relative to that for microbial life. We use a 1D radiative-convective climate and photochemical models to circumscribe a Habitable Zone for Complex Life (HZCL) based on known toxicity limits for a range of organisms as a proof of concept. We find that for CO 2 tolerances of 0.01, 0.1, and 1 bar, the HZCL is only 21%, 32%, and 50% as wide as the conventional HZ for a Sun-like star, and that CO concentrations may limit some complex life throughout the entire HZ of the coolest M dwarfs. These results cast new light on the likely distribution of complex life in the universe and have important ramifications for the search for exoplanet biosignatures and technosignatures.

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Demosponge steroid biomarker 26-methylstigmastane provides evidence for Neoproterozoic animals

Cited by 93 publications

References 38 publications

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid‐Proterozoic habitability

Global marine redox changes drove the rise and fall of the Ediacara biota

A Limited Habitable Zone for Complex Life

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