Polypeptides, Composed of Amino Acids, Perform the Indis

AMilIINO ACIDS IN PRECAMBRIAN SEDIMENTS: AN ASSA Y By J. WILLIAM SCHOPF, KEITH A. KVENVOLDEN, ANI) ELSO S. BARGHOORN

DEPARTMENT OF BIOLOGY, AND SOCIETY OF FELLOWS, HARVARD UNIVERSITY, CAMBRIDGE; EXO1IIOLOGY DIVISION, AMES RESEARCH CENTER, MOFFETT FIELD, CALIFORNIA; AND DEPARTMENT OF BIOLOGY, HARVARD UNIVERSITY Communicated \Tovember 16, 1967 Recent studies have documented the occurrence of organically and structurally preserved algae, bacteria, and other microorganisms of less certain affinities, in sediments of Early," 2 Middle,3-7 and Late Precambrian age.8' 9 1Iany of these organisms are irorphologically comparable to or identical with living thallo- phytes.9' 10 Investigations of hydrocarbons,"1 -3 porphyrins,'2 fatty acids,'4 and carbon isotopic ratios4' 15 in ancient sediments suggest basic biochemical simi- larities between Precambrian and extant organisms. To extend these studies, we have analyzed three fossiliferous Precambrian black cherts, ranging from about 1 to more than 3 billion years in age, for the presence of fossil amino acids. Our choice of amino acids for this preliminary survey is based on the following considerations: (1) Polypeptides, composed of amino acids, perform the indis- pensable role of mediating biochemical reactions in all known organisms; (2) analyses of Phanerozoic sediments and fossils'6' 17 and laboratory studies of reaction kinetics16-'8 have established that many amino acids are geochemically stable; (3) sensitive methods of amino acid analysis by cation-exchange chromatography'9 and by gas chromatography20 have been developed. Materials and Methods.-Samples: Black cherts from fosiliferous localities of the Fig Tree Series (Early Precambrian, South Africa), the Gunflint Iron Formation (Middle Precambrian, Ontario, Canada), aned the Bitter Springs Formation (Late Precambrian, Northern Territory, Australia) were analyzed for free and combined amino acids. All three cherts are dense, black, waxy, and somewhat lustrous on freshly broken conchoidal faces, and finely and rather irregularly laminated. They are composed of about 98% cryptocrystalline quartz, and contain 0.3-0.8% organic matter; they appear to be chemical sediments of primary, rather than secondary, origin. Each of the deposits has had a mild thermal history. Bacteriumlike microfossils' and algalike organic spheroids2 in the F' Tree cherts, having a minimum radiogenic age of 3.1 billion years,2' constitute the oldest structurally preserved evidence of life now known from the geologic record. Pris- tane, phytane, and n-alkanes have been reported from the Fig Tree sediments,2 22 and the C": C12 ratio of the indigenous organic matter,", as well as the geology and mineralogy of the sedimentary sequence,2 10 suggests the presence of photosynthetic organisms. The Fig Tree chert analyzed for amino acids was collected at the same locality and horizon from which microfossils have been reported.23 The Gunflint Iron Formation has a radiogenic age of approximately 1.9 billion years.4 The fossiliferous chert analyzed in the present study was collected near Schreiber, Ontario,24 at the type-locality for many of the twelve species of microscopic plants recognized in the well-documented Gunflint micro- biota.3-7 Pristane, phytane, and normal paraffins have been reported from these cherts,'3 as have Cl':C'2 ratios for both organic and inorganic carbon.4 Black cherts of the Bitter Springs Formation, from the Amadeus Basin of central Australia, contain at least 30 species of organically preserved microorganisms;8-0 chert from this fossiliferous locality25 was investigated for amino acids. Radiogenic age determinations indicate that these sediments are approximately 1 billion years old.9 Reagents and analytical controls: The commercially prepared chemicals used were of reagent grade; prior to use, all reagents were tested for amino acid content. Reagent 639 Downloaded by guest on September 24, 2021 640 BOTANY: SCHOPF ET AL. PROC. N. A. S.

grade ammonium hydroxide and hydrochloric acid were found to contain four amino acids (Ser, Gly, a-Ala, Asp)26 in concentrations of 10-8 to 10-9 M/liter. The NH40H used in these analyses was prepared from gaseous ammonia and triple-distilled water; no amino acids were detected in this reagent at a sensitivity of about 10-10 M/liter. Dis- tillation of reagent grade hydrochloric acid reduced the amino acid content by an order of magnitude, and only three amino acids (Ser, Gly, Asp) were detected. The quantities of these amino acids which could have been introduced during hydrolysis vary from more than 2 to over 4 orders of magnitude less than those detected in the chert extracts. All other reagents contained no detectable amino acids at a sensitivity of about 10-10 M/liter. An analytical blank (acid-cleaned glass beads), using commercially prepared ammonium hydroxide and hydrochloric acid, was carried through the entire analytical procedure. Trace amounts (<10-10 M/gm) of serine, glycine, a-alanine, and aspartic acid were detected. Using freshly prepared NH40H and distilled HCl, a second analytical blank (acid-cleaned quartz sand) was treated in the same manner as the rock samples, except that pulverization was omitted. These extracts were free of amino acids at a detection sensitivity of about 10-1" M/gm. Additional techniques were adopted to avoid introduction of contamination: objects coming in contact with the samples following hydrofluoric acid treatment (e.g., metal tongs, pulverizing equipment, glassware, etc.) were washed in a chromic-sulfuric acid solution and distilled water prior to use; filters were pre-extracted with hot 0.5 N NH4OAc, 6 N HCl (where appropriate), and hotH20, and were handled with acid-cleaned forceps; disposable plastic gloves, changed frequently, were worn throughout. Preparation of powdered chert: A hand-sized sample (500-800 gm) of chert from each of the three formations was mechanically cleaned, and immersed in a chromic-sulfuric acid solution overnight. The dried sample was broken into pieces which were fragmented in a jaw crusher, and the resulting 1/r to 1/rin. fraction was immersed in 25% hydro- ffwric acid until a total loss in dry weight of approximately 10% was measured (1/2-2 hr). After being thoroughly washed in triple-distilled water, the chalky-gray, etched chert fragments were ground for 2-6 min in a precleaned "shatter-box" disc pulverizern and the smaller than 115-mesh fraction (350-700 gm) was separated and stored in acid- cleaned bottles. At least 3 aliquots (50-100 gm each) of powdered chert from each sample were separately analyzed. Ammonium acetate leacn: In a typical analysis, 100 gm of <115-mesh chert powder was mixed on a magnetic stirrer with 400 ml 0.5 N ammonium acetate for '/2 hr at 80'C.21 The Teflon-coated stirring bar, with adhering iron filings derived from the pulverizer, was removed and the solution filtered through a Buchner funnel. The powdered chert was leached with 100 ml hot 0.5 N NH4OAc, followed by leaching with 500 ml hot triple- distilled water. The combined filtrate and leachate, containing free amino acids, was dried by evaporation under vacuum at 80°C, and the remaining ammonium acetate was removed by sublimation. HCl hydrolysis: The leached powder was placed in a 250-ml Erlenmeyer flask to which 100 ml distilled 6 N hydrochloric acid was added. The flask was partially evacuated, sealed, and placed in a constant temperature oven at 105°C for 22 hr.29 The greenish HCl hydrolysate was filtered through a Buchner funnel, and the residual powder was washed with 250 ml of hot triple-distilled water. The combined HC1 hydrolysate and washings, containing combined amino acids, was dried by evaporation under vacuum. Desalting procedure: The ammonium acetate leachate and the HC1 hydrolysate (pH adjusted to about 5.5), washed, respectively, onto the top of 100- and 200-cc chromatography columns packed with Bio-Rad AG 5OW-X8 cation-exchange resin, were deionized by flushing with 2-column vol of triple-distilled water; amino acids were collected in 4-column vol of 2 N ammonium hydroxide.s The NH40H eluants were dried by evaporation under vacuum at 80°C. Typically, 4 ml of triple-distilled water was added to the dry eluants, and the solutions were each divided into three fractions representing 1/4, 1/4, and 1/2 of the total extracts. These six fractions were dried by evaporation under vacuum at 60°C, and stored at- 5C. Downloaded by guest on September 24, 2021 VOL. 59, 1968 BOTANY: SCHOPF ET AL. 641 Identifcation of amino acids: Determination of amino acid content was carried out on a modified amino acid analyzer fitted with a microcolorimeter, using cation-exchange chromatography and spectrophotometry of ninhydrin-reacted products."' As is shown in Figure 1, all amino acids reported, with the exception of lysine and ornithine, are well resolved in this system. Dissolved in pH 2.2 citrate buffer, 1/4 of each extract was applied to the analyzer to determine acidic and neutral amino acid content, and 1/4 was used for determination of basic amino acids. The remaining half of each extract was investigated by gas chromatography. N-trifluoroacetyl n-butyl (N-TFA) ester derivatives of amino acids in the chert extracts were prepared according to the method of Gehrke and co-workers.20 Operating conditions for gas chromatography of these derivatives are given in Figure 3. Results.-Free amino acids: Relatively large amounts of glycine were de- TABLE 1. Amino acids in ammonium acetate leachates. Total free Age Glycine a-Alanine amino acids Sample (X 109yr) (nM/gm) (nM/gm) (nM/gm) Bitter Springs chert ca. 1.0 18.1 0.3 18.4 Gunflint chert 1.9 9.8 9.8 Fig Tree chert >3.1 5.9 5.9 tected in the ammonium acetate leachate of each of the three chert samples; a-alanine was present in minor amounts in the Late Precambrian Bitter Springs chert. The quantities listed in Table 1 represent average values based on amino acid analyzer chromatograms from at least three separate analyses, with a maxi- mum deviation of 11 per cent for the Bitter Springs chert, 9 per cent for the Gun- flint chert, and 10 per cent for the Fig Tree chert. Confirmatory identification of glycine and alanine in these extracts was obtained by gas chromatography of the N-TFA ester derivatives, based on both comparative retention times, and on coinjection of the samples with the appropriate authentic derivatives. Combined amino acids: Figure 1 shows amino acid analyzer chromatograms obtained from HOl hydrolysates of the three Precambrian cherts. The quanti-

Lys.Orn

e Neu hs f ~~~~IArg

Tyr Ph* r-A-Aot STANDRD Pro N..Ek_ i I (Cyne-VAbs Xb)-

.eUNFLINT CHERT

FH3 TREE CHERT FiG. 1.-Amino acid analyzer chromatograms of HOl hydrolysates of three Precambrian cherts. Abbreviations for amino acids are listed in Fig. 2. Downloaded by guest on September 24, 2021 642 BOTANY: SCHOPF ET AL. PROC. N. A. S.

HCI Hydrolysate

acid Bitter Springs Chert (47.0 nM/g)

2 Gunflint Chert (18.3nM/)

Fig Tree Chert (12.2nM/g)

soluciOne l Rola n - Alonine Amino butyric acid Phonylabonine Lysin* + Ornithine Tyrosine allo-isoloucine Histidin* Eli ~~~~~~~~I ICys teic ocid

FIG. 2.-Histogram showing distribution of amino acids in HCO hydrolysates of the Bitter Springs chert (ca. 1.0 X 109 years old), the Gunflint chert (1.9 X 109 years old), and the Fig Tree chert (>3.1 X 109 years old). ties shown in Figure 2 represent average values based on triplicate analyses of each sample, with a deviation of 7 + 3 per cent for the Bitter Springs amino acids, 8 ± 4 per cent for those from the Gunflint hydrolysate, and 10 4 4 per cent for the amino acids of the Fig Tree chert. Identification of 11 of the amino acids detected in these hydrolysates (Gly, a-Ala, Glu, Asp, Leu, Val, Ser, Thr, Ileu, Pro, b-Ala) was confirmed by gas chromatography of their N-TFA ester derivatives. A gas chromatogram of the derivatives from the Fig Tree hydrolysate is shown in Figure 3. Because of limitations on sample size, the identification of several amino acids (Phe, allo-Ileu, MIet, amino butyric acids) could not be confirmed by this technique. Derivatives of other amino acids (Lys, Orn, Tyt, His, Arg) would not be detected under the conditions employed.20, 30 Discussion.-The interpretation of these results is dependent on four basic considerations: (1) Are the reported compounds correctly identified? (2) Downloaded by guest on September 24, 2021 VOL. 69, 1968 BOTANY: SCHOPF ET AL. 643

FIG. 3.-Gas chromatogram Wy of N-TFA ester derivatives of Srpr amino acids in HC1 hydrolysate I-Ala Thr of Early Precambrian Fig Tree NO- bu chert. Abbreviations for amino acids are listed in Fig. 2. Operating conditions: Perkin- STANDARD Elmer F-li flame-ionization CHROMATOGRA G.C.; Carbowax 20M, 0.02 in. I.D., 50 ft; N2 = 7 ml/min, H2 = 10 ml/min; chart speed = 1 in./10 min. PM0 TRWEMC

Are these compounds indigenous to the rock samples analyzed? (3) Are the organic compounds syngenetic with original sedimentation? (4) Are the compounds biogenic? Although only three Precambrian sediments have been investigated in this preliminary study, and the data are therefore somewhat limited, these questions can be answered, at least tentatively, in the affirmative. Identification: The identification of amino acids in extracts of the three Pre- cambrian cherts is based on amino acid analyzer chromatograms, in part confirmed by gas chromatography of the N-TFA ester derivatives. This appears to be the first report of gas chromatographic identification of amino acids from geologic materials. Solubility properties of these compounds, and their chromatographic characteristics on desalting columns, are similarly characteristic of amino acids. Identification of these compounds seems well established. Indigenousness: In analyzing sedimentary rocks for low concentrations of amino acids, care must be taken to avoid contamination from two major sources: (a) sample contamination from contemporary plant fragments, microorganisms, and other organic matter on surfaces of the rock sample; and (b) laboratory contamination from hands, reagents, glassware, etc. Sample contamination was minimized by immersing the chert specimens in a sulfuric-chromic acid solution, followed by coarse crushing and treatment with hydrofluoric acid. Scrupulous care was taken to avoid laboratory contamination. The success of these techniques is evidenced by the results obtained by analyses of analytical blanks. The indigenous nature of the amino acids detected is further supported by the following five considerations: (1) The absence of contamination from fingerprints is evidenced by the detection of only two amino acids (Gly and Ala) in the ammonium acetate leachates; fingerprints normally contain at least 17 free amino acids including citrulline,31 a nonprotein amino acid not detected in the chert extracts. (2) The absence of hand contamination is further indicated by a lack of similarity between the amino acid content of the chert hydrolysates and the distribution reported from hydrolyzed hand rinses,31-33 and by the detection of several nonprotein amino acids (b-Ala, allo-Ileu, amino butyric acids) not present in human hands. (3) Triplicate analyses of each rock sample show quantitative and qualitative consistency, and the three cherts differ in amino acid con- Downloaded by guest on September 24, 2021 644 BOTANY: SCHOPF ET AL. PRoc. N. A. S.

tent. This distribution is unrelated to the order of analysis: the samples were analyzed sequentially inl order of decreasing geologic age, increasing geologic age, and a third sequence in which the sample of intermediate age was analyzed first. (4) Analyses of both 50- and 100-gm aliquots of powdered chert demonstrate that the quantities of amino acids detected vary in direct proportion to the amount of sample extracted. (5) Amino acids have been detected in different samples of the Bitter Springs chert at two different laboratories. 34 Syngenesis: Although the evidence indicates that the amino acids are almost certainly indigenous to the chert samples, it is somewhat more difficult to establish that these compounds are syngenetic with original sedimentation, and are therefore the same age as the sediments in which they have been detected. This problem arises because techniques are unavailable for direct dating of the organic fraction of ancient rocks. Geologic and geochemical considerations, however, suggest that the amino acids detected are of great geologic age, and most probably were emplaced at the time of original sedimentation. Because of their relatively high degree of impermeability and incompressi- bility, primary cherts are excellent sediments for organic geochemical studies. The petrology and mineralogy of the three cherts analyzed indicates that they are essentially unmetamorphosed, and none has been recrystallized. On the basis of petrologic and geologic evidence, it has been established that most, and presum- ably all, of the organic matter in these deposits was emplaced prior to lithifica- tion, at the time of original sedimentation.2 4 9 Chemical evidence suggests that the amino acid distribution in these sediments has been geochemically altered since original deposition. Of particular signfi- cance is the occurrence of several nonprotein amino acids (b-Ala, allo-Ileu, amino butyric acids), reported to be products of the geochemical degradation of more common amino acids."8 35 The presence of only two free amino acids, glycine and a-alanine, seems attributable to their inherent geochemical stability, and to the fact that they are degradation products of less stable amino acids.8' 35 Although only thermally stable amino acids were detected in the ammonium acetate leachates, several less stable compounds (e.g., Thr, Met, Ser, _ Arg) were freed from the cherts by is.~~~ _ This distribution 40- z HCI hydrolysis. E is consistent with other studies 230- which suggest that geochemical 0 stability may be enhanced by che- lation with an inorganic or organic C 'Totol Amino Acids Z 7_ *.Combi.ned Anino Acids phase.36' 37 C- X - Free Amino Acids '.. As is shown in Figure 4, the 5.Fi 1 i 2 3 quantity of amino acids detected is Age in Billions of Years inversely related to the radiometric FIG. 4.-Semi-log plot of total, combined, and age of the cherts. Although plotted free amino acid content of the three Precambrian in terms of nanomoles of amino cherts investigated. Note the approximately exponential decrease (dotted line) in free amino acids per gram of chert, a similar acid content with increasing age. trend would result if the data were Downloaded by guest on September 24, 2021 VOL. 59, 1968 BOTANY: SCHOPF ET AL. 645

plotted as nM/gm organic matter, since the three sediments contain quite similar amounts of organic material. If the three (cherts initially contained comparable quantities of anmino acids, this trend could be interpreted as resulting from gradual chemical degradation, and since the sediments have had similar geologic histories, a comparison of the residual amino acid content would indicate relative geologic age. The apparently exponential decrease in free amino acid content could be interpreted as resulting primarily from the degradation of glycine by a first-order irreversible reaction.'7 18 Based on the preliminary data available, such an interpretation would be premature. Data from other Pre- cambrian cherts, and from additional samples of the three sediments investigated, are needed to establish that the observed trend is not merely fortuitous. Biogenicity: Complex organic compounds have been abiotically synthesized under conditions similar to those postulated for the primitive earth.38 Few criteria are available to enable discrimination between biologically and abiotically produced organic compounds, and amino acids are readily formed by abiotic means. Although it might be suggested, therefore, that the amino acids here reported from Precambrian rocks are of nonbiological origin, the available evidence seems indicative of biogenicity. Perhaps the most telling argument for the biological origin of these compounds is the fact that they are associated with organically preserved microfossils.'-9 It may also be noted that the distribution of amino acids in the chert extracts differs from typical distributions reported from abiotic syntheses,38 and that all of the amino acids detected are either known from extant organisms or are apparently geochemical derivatives of biological amino acids. New techniques for gas chromatographic analysis of amino acid isomers39 may provide additional evidence relating to the origin of these apparently biogenic compounds. Summary and Conclusions.-Three fossiliferous Precambrian cherts, approximately 1, 2, and 3 billion years in age, were analyzed for the presence of amino acids. Small but measurable quantities of one or two free amino acids (10-8 to 10-9 M/gm), and 21 or 22 combined amino acids (10-8 M/gm) were detected in triplicate analyses of each sediment. Determination of amino acid content is based on amino acid analyzer data, and the identification of 11 amino acids was confirmed by gas chromatography of the N-TFA ester derivatives. Several lines of evidence indicate that the amino acids are indigenous to the rock samples investigated, and geologic and geochemical considerations strongly suggest that these compounds date from the time of original sedimentation. In general, there appear to be few qualitative differences in amino acid distribution between the three Precambrian cherts, but the quantity of amino acids detected per gram of sediment decreases with increasing geologic age. Although the stereoisomeric nature of the amino acids has not been determined, their association with organically preserved microorganisms seems indicative of a biological, rather than an abiotic, origin. These preliminary findings are consistent with earlier studies which indicated that biochemically complex organisms were in existence more than 3.1 billion years ago," 2, 10 and they suggest that the amino acid composition of living systems has not changed significantly since very early in biological history. Downloaded by guest on September 24, 2021 646 BOTANY: SCHOPF ET AL. PROc. N. A. S.

We thank Dr. Egon T. Degens, Woods Hole Oceanographic Institution, for suggestions relating to analytical procedure and for allowing J. W. S. to carry out preliminary analyses in his laboratory. We also thank Dr. Cyril Ponnamperuma for making available the facilities of the Ames Research Center to J. W. S., and Dr. Sam Aronoff, Iowa State Uni- versity, for helpful advice regarding laboratory techniques. * This work supported in part by NSF grant GA-1115 to Harvard University. 'Barghoorn, E. S., and J. W. Schopf, Science, 152, 758 (1966). 2 Schopf, J. W., and'E. S. Barghoorn, Science, 156, 508 (1967). 3Tyler, S. A., and E. S. Barghoorn, Science, 119, 606 (1954). 4Barghoorn, E. S., and S. A. Tyler, Science, 147, 563 (1965). 6 Schopf, J. W., E. S. Barghoorn, M. D. Maser, and R. 0. Gordon, Science, 149, 1365 (1965) 6 Cloud, P. E., Jr., Science, 148, 27 (1965). 7Cloud, P. E., Jr., and H. Hagen, these PROCEEDINGS, 54, 1 (1965). 8 Barghoorn, E. S., and J. W. Schopf, Science, 150, 337 (1965). 9 Schopf, J. W., J. Paleontol., in press. 10Schopf, J. W., in McGrau,-Hill Yearbook of Science and Technology (1967), p. 46. 11 Johns, R. B., T. Belsky, E. D. McCarthy, A. L. Burlingame, P. Haug, H. K. Schnoes, W. Richter, and M. Calvin, Geochim. Cosmochim. Acta, 30, 1191 (1967). 12Barghoorn, E. S., W. G. Meinschein, and J. W. Schopf, Science, 148, 461 (1965). 13 0r6, J., D. W. Nooner, A. Zlatkis, S. A. Wikstrbm, and E. S. Barghoorn, Science, 148, 77 (1965). 14Hoering, T. C., and P. H. Abelson, Carnegie Institution of Washington Year Book 64 (1965), p. 218. 15 Hoering, T. C., Carnegie Institution of Washington Year Book 64 (1965), p. 215. 16Jones, J. D., and J. R. Vallentyne, Geochim. Cosmochim. Acta, 21, 1 (1960). 17Abelson, P. H., in Organic Geochemistry, ed. I. A. Breger (New York: Pergamon Press, 1963), p. 431. 18Vallentyne, J. R., Geochim. Cosmochim. Acta, 28, 157 (1964). 19 Moore, S., and W. H. Stein, J. Biol. Chem., 211, 893 (1954). 20 Gehrke, C. W., and D. L. Stalling, Separ. Sci., 2, 101 (1967). 21Ulrych, T. J., A. Burger, and L. 0. Nicholaysen, Earth Planet. Sci. Letters, 2, 179 (1967) 22 Or6, J., and D. W. Nooner, Nature, 213, 1082 (1967). 23Black chert facies in upper third of Fig Tree Series, exposed by road cutting 100 m north- west of surface opening to Daylight Mine (Barbrook Mining Co.), 28 km east-northeast of Barberton, South Africa. Collected by E. S. B., February 1965. 24 Lower Algal Chert Member of Gunflint Iron Formation, exposed on northern shore of Lake Superior, 6.4 km west of Schreiber, Ontario. Collected by J. W. S. and E. S. B., August 1966. 25 Black chert facies in middle third of Bitter Springs Formation, exposed on south slope of ridge about 1.6 km north of Ross River Tourist Camp (Love's Creek Homestead), 64 km east- northeast of Alice Springs, Northern Territory, Australia. Collected by E. S. B., April 1965. 26 Abbreviations for amino acids are listed in Fig. 2. 27 T-250 Laboratory Disc Mill, Angstrom, Inc., Chicago, Ill. 28 Degens, E. T., and J. H. Reuter, in Advances in Organic Geochemistry (New York: Per- gamon Press, 1964), p. 377. 29 Hydrolysis of this type, in the presence of oxygen, results in the quantitative oxidation of cystine to cysteic acid and the partial destruction of methionine.31 30 Pollock, G. E., Anal. Chem., 39, 1194 (1967). 31 Hare, P. E., Carnegie Institution of Washington Year Book 64 (1965), p. 232. 32 0ro, J., and H. B. Skewes, Nature, 207, 1042 (1965). 33Hamilton, P. B., Nature, 205, 284 (1965). 34Analyses here reported were carried out at the Ames Research Center; preliminary analyses of the Bitter Springs chert were carried out at the Woods Hole Oceanographic Institu- tion, through the courtesy of Dr. E. T. Degens. 35 Hare, P. E., and R. M. Mitterer, Carnegie Institution of Washington Year Book 65 (1966), p. 362. 36 Degens, E. T., J. M. Hunt, J. H. Reuter, and W. E. Reed, Sedimentology, 3, 199 (1964). 37 Degens, E. T., Geochemistry of Sediments (Englewood Cliffs, N.J.: Prentice-Hall, 1965), 342 pp. 38Ponnamperuma, C., and N. W. Gabel, Space Life Sci., in press. 39 Pollock, G. E., and V. I. Oyama, J. Gas Chromatog., 4, 126 (1966). Downloaded by guest on September 24, 2021