Grain trapping by microbial mats: Implications for stromatolites Frank Corsetti Department of Earth Sciences University of Southern California Rocks = Time Rocks = Environment Rocks = History of Life Stromatolite sharkbay.org Stromatolite Textbook Definition • laminated • organo-sedimentary structure • built by microbes (CCALA) Cyanobacteria Cyanobacteria microbial mat (“pond scum”) Stromatolite Textbook Definition Trapping and Binding 100 microns Stromatolite courtesy of Y. Ibarra Textbook Definition Mineral Precipitation Stromatolite Significance • Macroscopic from Microscopic Stromatolite Significance putative • Oldest fossils in the world ^ Warrawoona Fm Western Australia 3.5 Ga 2 cm Ancient Life: Greatest Hits Cambrian explosion Hadean Archean Proterozoic Phan. 4.0 3.0 2.0 1.0 0 billions of years LETTERS NATURE | Vol 457 | 5 February 2009 Masirah Bay Fm. soft-body parts, as detected in Doushantuo phosphorites19,22, is rare in ααα ααα αββ the geological record. Siliceous sponge spicules are metastable and S R C (17%) they can be difficult to isolate and identify unambiguously in clastic 26 sediments. Moreover, several orders of Demospongiae completely *** * 358 → 217 lack mineral skeletons. On the other hand, the studies of the lipid ααα ααα compositions of Porifera show a remarkable diversity of distinctive αββ C27 (21%) 13,27,28 R structures with abundance patterns aligned to phylogeny S 372 → 217 The demosponge biomarker record for the Huqf Supergroup supports the hypothesis that Metazoa first achieved ecological 1 αββ ααα ααα prominence in shallow marine waters of the Cryogenian . It has been C28 (16%) 386 → 217 proposed that Neoproterozoic sponges and rangeomorphs feeding S R on reactive dissolved or particulate marine organic matter29 may have progressively oxygenated their benthic environments as they moved ααα ααα αββ 24 C29 (39%) from shallow water into deeper waters . Consistent with this, our R S 400 → 217 data (Table 1 and Suplementary Table 1) show that, on average, C30 Signal intensity (a.u.) steranes comprised 2.7% of total C27–C30 extractable steranes in Huqf samples and 63% of the summed C30 compounds were 24- C30 (5%) (24-i/24-n) = 1.35 ++ isopropylcholestanes, suggesting that demosponges must have made ° ° + + 414 → 217 ° a significant contribution to preserved sedimentary organic matter and, therefore, environmental biomass24. In contrast, lack of signifi- cant sponge steranes in deepwater shales from the Ediacaran Rodda Bed Formation in the Officer basin, Australia15, and from the late Cryogenian Aralka Formation (Supplementary Information) sug- Ghadir Manquil Fm. ααα gests that it took longer to colonize deepwater environments. ααα αββ Neoproterozoic sponges would have been at least partly responsible S R for the ultimate respiration and removal of dissolved organic C26 (9%) ** 24,29 * * (*) 358 → 217 carbon , aiding ventilation of the global ocean and shifts in the ααα modes of carbon and sulphur cycling evident from Ediacaran iso- αββ ααα topic and geochemical records3,30. R C (17%) S 27 372 → 217 METHODS SUMMARY αββ Solvent-rinsed core rock fragments and cuttings were crushed to a fine powder ααα ααα C28 (12%) using an alumina ceramic puck mill housed in a SPEX 8510 shatterbox. Rock R S 386 → 217 powders were extracted with a mixture of dichloromethane and methanol (9:1, v/v) using a Dionex Accelerator Solvent Extractor ASE-200 operated under αββ ααα ααα 1,000 p.s.i. at 100 uC. Asphaltenes were precipitated from the resulting organic C (55%) 29 extracts (bitumens) using n-pentane. The maltenes (n-pentane solubles) were R S Signal intensity (a.u.) Ancient Life: Greatest 400Hits → 217 then fractionated by silica gel adsorption chromatography, eluting successively with hexane, hexane/CH2Cl2 (v/v: 4:1) and CH2Cl2/CH3OH (v/v: 3:1) to yield saturated hydrocarbons, aromatic hydrocarbons and resin fractions, respectively. C (7%) 30 Continuous-flow hydropyrolysis experiments were conducted on 100– 414 → 217 (+) 2,000 mg of catalyst-loaded pre-extracted sediments or kerogen concentrates (24-i/24-n) = 1.31 + + + as described previously7 ° ° °+ . Hydropyrolysates were fractionated on silica gel col- umns, as for rock bitumens. GC-MS analyses of saturated hydrocarbon fractions were performed on a Love et al., 2009 Retention time (min) Micromass AutoSpec Ultima equipped with a HP6890 gas chromatograph and Figure 2 MRM GC-MS ion chromatograms of C –C desmethylsteranes a DB-1MS coated capillary column (60 m 3 0.25 mm i.d., 0.25-mm film thick- | 26Sponge30 Biomarkers released from catalytic hydropyrolysis of a Masirah(Oldest Bay Formation Animal) (JF-1) ness) using He as carrier gas. Hopane and sterane biomarkers were analysed by and a Ghadir Manquil Formation (GM-1) kerogen. For each sterane carbon MRM GC-MS with a total cycle time of 1.3 s per scan for 26 transitions, including number,Hadean four diastereoisomersArchean are detectedProterozoic (aaa20R, abb20R,Phan.abb20S, the m/z 414 to 217 transition for C30 desmethylsteranes. The GC oven was 21 aaa20R), indicating4.0 a mature3.0 geoisomer2.0 distribution.1.0 Demosponge 0 programmed at 60 uC (2 min), heated to 150 uCat10uC min , further heated contributions are evident from abundantbillions of years 24-isopropylcholestanes (‘plus’ to 315 uCat3uC min21 and held at final temperature for 24 min. signs). 24-n-propylcholestanes (open circles) are markers of marine 50 ng of deuterated C29 sterane standard [d4-aaa-24-ethylcholestane (20R)] pelagophyte algae and this confirms a marine depositional setting for each was typically added to 1 mg saturates to quantify the polycyclic biomarker con- formation in the SOSB. Stars mark a series of 27-norcholestanes. At right, tent. Yields assume equal mass spectral response factors between analytes. values in parentheses represent a measure of relative signal intensity for the Analytical errors for individual hopanes and steranes concentrations are esti- C26–C30 steranes in acquired MRM chromatograms (though absolute mated at 630%. Average uncertainties in hopane and sterane biomarker ratios abundances are determined from individual peak areas) and the numbers are 68% as calculated from multiple analyses of a saturated hydrocarbon frac- beneath are the masses (in daltons) of the ion transitions (molecular weight tion from an AGSO standard oil (n 5 30). R fragment ion) used in MRM GC-MS in each case. y axis, signal intensity; x axis, retention time in min (52 to 68 min shown for all traces). Full Methods and any associated references are available in the online version of the paper at www.nature.com/nature. biomarker appearance corresponds well to divergence estimates for Received 23 September; accepted 27 November 2008. the last common ancestor of all living demosponges obtained from molecular clocks25,26, and indeed can now be used to more robustly 1. Peterson, K. J., Cotton, J. A., Gehling, J. G. & Pisani, D. The Ediacaran emergence of calibrate the molecular clock at the base of the animal tree1. bilaterians: Congruence between the genetic and the geological fossil records. Phil. Trans. R. Soc. B 363, 1435–1443 (2008). The use of recalcitrant lipid biomarkers offers a promising 2. Bowring, S. A. et al. Geochronologic constraints on the chronostratigraphic approach for tracking the earliest sponge contributions to framework of the Neoproterozoic Huqf Supergroup, Sultanate of Oman. Am. J. Sci. Precambrian sedimentary rocks because outstanding preservation of 307, 1097–1145 (2007). 720 ©2009 Macmillan Publishers Limited. All rights reserved Ancient Life: Greatest Hits Grypania Oldest putative eukaryote Hadean Archean Proterozoic Phan. 4.0 3.0 2.0 1.0 0 billions of years 244 Ancient Life:K. SugitaniGreatest et al. / Precambrian Hits Research 158 (2007) 228–262 20 microns Sugitani et al., 2007 Oldest putative microfossils Hadean Archean Proterozoic Phan. 4.0 3.0 2.0 1.0 0 billions of years Fig. 11. Photomicrographs of spheroidal microstructures. Scale bar: 20 ␮m (a, c–n); 10 ␮m (b). (a), (b) and (l–n) from Mount Grant and others from Mount Goldsworthy. Also see Supplementary Fig. III.(a)Colony-likeaggregationofsmallspheroidalmicrostructures.SlideNORW1,Position L-J50/2. (b) Magnification of (a). I, Nearly completely hollow sphere; II, distorted sphere; III, ruptured sphere; IV, cluster of opaque particles. (c) and (d) Polar and equatorial views of a large hollow spheroidal microstructures. Arrow shows the deepening focal depths. Slide GWM11A-sub2, Position L-R35. (e) Hollow spheroidal microstructures. Slide GWM11A-sub1, Position L-S46/4. (f–h) Views of hollow spheroidal microstructures with possible inner spheroidal object. The arrow shows the deepening focal depths. Slide NGWM1X, Position R-N40/1. (i) Slightly distorted hollow spheroidal microstructures with partially wrinkled wall. Slide NGWM3, Position R-L37/3. (j) Broken? spheroidal microstructure. Slide NGWM1X, Position R-F40/1. (k) Non-hollow spheroidal microstructure. Slide GWM11A-EX1, Position L-E38/3. (l and m) Distorted spheroid. Slide NORW1X-1’, Position L-O59. (n) Semi-hollow spheroid with partly broken left margin. Slide GFWE3-1, Position L-O61. Ancient Life: Greatest Hits OMin OR Oldest “Uncontroversial” Stromatolite Hadean Archean Proterozoic Phan. 4.0 3.0 2.0 1.0 0 billions of years Pondering Geologic Time The rest of Geologic Time (~886 more sheets) A Microbial World! Hadean Archean Proterozoic Phan. 4.0 3.0 2.0 1.0 0 billions of years Us 1 million years 2 million years Lucy 3 million years 4 million years Hadean Archean Proterozoic Phan. 4.0 3.0 2.0 1.0 0 billions of years Modern stromatolites as analogues for ancient stromatolites? Grain size >250 µm 4 cm Bahamas Shark Bay Modern Modern Grain-Size Conundrum Stromatolite grain size through time coarse-grained stromatolitescoarse-grained & thrombolites stromatolites Stromatolite grain size through time fine-grained stromatolites & thrombolites coarse-grained stromatolites & thrombolites ArcheanStromatolite grain sizeProterozoic through time Phan. 3.5 2.5 1.5 0.5 fine-grainedbillions stromatolites of years & thrombolites coarse-grained stromatolites & thrombolites Archean Proterozoic Phan. 3.5 fine-grained2.5 stromatolites &1.5 thrombolites 0.5 billions of years Archean Proterozoic Phan.