Elso S. Barghoorn

Microorganisms Three Billion Years Old from the Precambrian of South Africa

A minute, bacterium-like, rod-shaped organism, Eobacterium isolatum, has been found organically and structurally preserved in black chert from the Fig Tree Series (3.1 x 109 years old) of South Africa. Filamentous organic structures of probable biological origin, and complex alkanes, which apparently contain small amounts of the isoprenoid hydrocarbons pristane and phytane, are also indigenous to this Early Precambrian sediment. These organic remnants comprise the oldest known evidence of biological organization in the geologic record.

Late Quaternary Sea-Level Change and Crustal Rise at Boston, Massachusetts, with Notes on the Autocompaction of Peat

The compression of peat beneath its own weight (autocompaction) is discussed, and it is shown that because of this process radiocarbondated samples of salt-marsh peat or peaty sediment, other than very thin samples cut from the base of the deposit, cannot be correlated with sea level without construction of a sea-level change curve from other types of data. With rising sea level there is a maximum thickness of salt-marsh peat for any given productivity of marsh grass. Because of this limitation, most marshes older than about 5500 years B.P. have been drowned. An important effect of peat autocompaction is the intrusion of wood into older peat horizons and the juxtaposition of wood of different ages. Wood, therefore, should be avoided in the dating of peat profiles. The roots of salt-marsh plants generally descend a foot or more beneath the rhizomes, contaminating older horizons insofar as radiocarbon dating is concerned. This contamination tends to make dates from marsh samples err on the young side. Sixteen radiocarbon dates from the Boston area are used to construct a sea-level curve going back to 14,000 years B.P. Relative sea level was at +60 feet or higher 14,000 years B.P., dropping sharply to approximately −70 feet about 10,000 years B.P. From a low of −70 feet, sea level rose steadily to about −2 feet approximately 3000 years B.P. Since then sea level appears to have kept close to its present level, probably fluctuating about a foot during the course of the stillstand. A crustal movement curve, based on the relative sea-level curve for Boston and the eustatic curve, indicates that about 290 feet of crustal rise occurred between 14,000–6000 years B.P., with a maximum rate of uplift of about 0.2 foot per year at 12,750 years B.P., and that from 6000 to 3000 years B.P., crustal subsidence occurred at Boston.

Alga-Like Fossils from the Early Precambrian of South Africa

Micropaleontological studies of carbonaceouis chert from the Fig Tree Series of South Africa (> 3.1 x 109 years old) revealed the presence of spheroidal microfossils, here designated Archaeosphaeroides barbertonensis, interpreted as probably representing the remnants of unicellular alga-like organisms. The presumed photosynthetic nature of these primitive microorganisms seems corroborated by organic geochemical and carbon isotopic studies of the Fig Tree organic matter, and is consistent with the geologically and mineralogically indicated Early Precambrian environment. These alga-like spheroids, together with a bacterium-like organism previously described from the Fig Tree chert, are the oldest fossil orgisms now known.

THE GUNFLINT MICROBIOTA

The microbiota of the Gunflint Iron Formation (∼2 Ga old) is sufficiently great in diversity as to represent a “benchmark” in the level of evolution at a time only somewhat less than intermediate between the origin of the earth and the present. To date, thirty entities from these ∼2 Ga old microfossiliferous cherts have been described and all but two systematically categorized. From our continuing detailed study of the Gunflint microbiota (ESB for over 20 years) and, in light of our recent investigations on blue-green algal cell degradation, we conclude that: (1) A considerable number of the taxa systematically described are either of doubtful biological origin, doubtful taxonomic assignment, and/or morphologically indistinguishable from previously described Gunflint microorganisms, (2) The microbiota is wholly prokaryotic. At present, we recognize sixteen taxa falling within three categories: (1) blue-green algae (6 taxa; e.g. Gunflintia minuta); (2) budding bacteria (4 taxa; e.g. Eoastrion simplex); and (3) unknown affinities (6 taxa; e.g. Eosphaera tyleri). Organisms of undoubted eukaryotic affinities have yet to be found in the Gunflint. The Gunflint assemblage includes a high percentage of morphologic entities of obscure taxonomic position. Recently, Walter (1975) and Knoll and Barghoorn (1975) reported Gunflint-type microbiotas of approximately the same age as the Gunflint from two localities in Australia. The dominant morphotypes of the Gunflint microbiota appear to be cosmopolitan and the striking similarity of the three assemblages may strengthen the potential of ancient microbiotas for use in Precambrian biostratigraphy.

Paleobiology of a Precambrian Shale: Geology, organic geochemistry, and paleontology are applied to the problem of detection of ancient life.

Investigations have been made of crude oil, pristane, phytane, steranetype and optically active alkanes, porphyrins, microfossils, and the stable isotopes of carbon and of sulfur found in the Nonesuch shale of Precambrian age from Northern Michigan. These sediments are approximately 1 billion years old. Geologic evidence indicates that they were deposited in a nearshore deltaic environment. Porphyrins are found in the siltstones but not in the crude oils of the Nonesuch formation—evidence that these chemical fossils are adsorbed or absorbed and immobile. This immobility makes it highly unlikely that these porphyrins could have moved from younger formations into the Nonesuch sediments, and the widely disseminated particulate organic matters and fossils in this Precambrian shale are certainly indigenous.

Microorganisms from the Late Precambrian of Central Australia

An assemblage of structurally and organically well preserved microorganisms, interpreted as both green and blue-green algae, has been found in chert facies of the Bitter Springs limestone from the upper Precambrian of central Australia. This appears to be the earliest known occurrence of green algae in the fossil record. These organisms are among the oldest known multicellular and unicellular fossils exhibiting distinct histological preservation.

On the experimental silicification of microorganisms II. On the time of appearance of eukaryotic organisms in the fossil record

Abstract On the basis of ultrastructural, biochemical and genetic studies, bacteria and blue green algae (Kingdom Monera, all prokaryotes) differ unambiguously from the eukaryotic organisms (Fungi, plants sensu stricto ) and protists or protoctists, (Copeland, 1956). The gap between eukaryotes and prokaryotes is recognized as the most profound evolutionary discontinuity in the living world. This gap is reflected in the fossil record. Fossil remains of Archaean and Proterozoic Aeons primarily consist of prokaryotes and the Phanerozoic is overwhelmingly characterized by fossils of the megascopic eukaryotic groups, both metazoa and metaphyta. Based on the morphological interpretation of microscopic objects structurally preserved in Precambrian cherts, the time of appearance of remains of eukaryotic organisms in the fossil record has been claimed to be as early as 2.7 · 10 9 years ago, (Kaźmierczak, 1976). Others suggest chronologies varying between 1.7 to 1.3 · 10 9 (Schopf et al., 1973) or a time approaching 1.3 · 10 9 years (Cloud, 1974). There is general agreement that many of the Ediacaran faunas, which have been dated at about 680 m.y. are fossils of megascopic soft-bodied invertebrate animals. Since all invertebrates are eukaryotic, the ca. 680 m.y. date for deposition of these animal assemblages may represent the earliest appearance of eukaryotic organisms. But the question remains as to whether there is definitive evidence for eukaryotic cells before this “benchmark” of the late Precambrian. An excellent discussion of this particular problem as especially relating to acritarchs extending from rocks of Upper Riphean through Vendian and into the basal Cambrian is presented in recent studies by Vidal (1974, 1976) in Late Precambrian microfossils from the Visingso rocks of southern Sweden. Previous work on the laboratory silicification of wood and algal mat communities (Leo and Barghoorn, 1976) suggested that further analysis of “artificial fossils” might be of aid in the interpretation of fossil morphology toward the ultimate solution of this problem. Thus the procedure developed by one of us (ESB) for laboratory wood silicification was adapted to various smaller objects. By successive immersions of wet cellular aggregates, colonies of various organisms and abiotic organic microspheres in tetraethyl orthosilicate, silicified cells and structures are produced which bear an interesting resemblance to ancient chert-embedded microfossils. Our observation of these microorganisms and proteinoid microspheres silicified in the laboratory as well as of degrading microorganisms, both eukaryotic and prokaryotic, have led us to conclude that many, if not all, of the criteria for assessing fossil eukaryotic microorganisms are subject to serious criticism in interpretation. We studied a large variety of prokaryotic algae, some eukaryotic algae, fungi, protozoa, and abiotic organic microspheres stable at essentially neutral pH. In some cases, degradation and/or silicification systematically altered both size and appearances of microorganisms. By the use of monoalgal cultures of blue-green algae, features resembling nuclei, chloroplasts, tetrads, pyrenoids, and large cell size may be simulated. In many cases individual members of these cultures show so much variation that they may be mistaken as belonging to more than one species. The size ranges for silicified prokaryotic and eukaryotic algae overlap. Several prokaryotes routinely yielded spherical or filamentous structures that resembled large cells. Because of genuine large sizes (e.g., Prochloron ), shrinkage, systematic alteration or congregation of unicells to form other structures we find sizes to be of very limited use in determining whether an organism of simple morphology was prokaryotic or eukaryotic. Although some “prebiotic proteinoid microspheres” (of Fox and Harada, 1960) are impossible to silicify with our laboratory methods, those stable at neutral pH (Hsu and Fox, 1976) formed spherical objects that morphologically resemble silicified algae or fungal spores. Many had internal structure. We conclude that even careful morphometric studies of fossil microorganisms are subject to many sources of misinterpretation. Even though it is a logical deduction that eukaryotic microorganisms evolved before Ediacaran time there is no compelling evidence for fossil eukaryotes prior to the late Precambrian metazoans.

Hydrocarbons of Biological Origin in Sediments about Two Billion Years Old

Normal paraffins in the C16 to C32 range and the saturated isoprenoid hydrocarbons, pristane and phytane, have been found in chert from the Gunflint iron formation (1.9 x 109 years old) of the north shore of Lake Superior. The distribution of n-alkanes shows two maxima, one at about C18 to C19 and the other at about C22 with a minimum occurring at C20 to C21. No predominance of odd- to even-carbon-number alkanes is observed within the C16 to C32 range. The results agree with micropaleontological observations made on the Gunflint chert and provide a chemical characterization of Precambrian life existing about two eons ago.

The Microbial Community in the Layered Sediments at Laguna Figueroa, Baja California, Mexico: Does it Have Precambrian Analogues?

Abstract In the hypersaline lagoon at Laguna Figueroa vertically stratified diverse communities of microorganisms thrive. The modern sediments of Baja California at Laguna Figueroa contain cyanobacterial communities and sedimentary structures produced by these blue greens that have already been studied by Horodyski and his colleagues. This paper provides an introduction to the complex microbial communities, primarily those that underlie the laminated Microcoleus mats. They are composed of anaerobic photosynthetic and heterotrophic bacteria. The following genera of cyanobacteria at least are components of these mat communities: Lyngbya, Microcoleus, Entophysalis, Phormidium, Pseudoanabaena, Anabaena and Schizothrix. Among the photosynthetic bacteria several species of Thiocapsa-like microbes formed major surface components of certain mats and scums; rhodospirilli, rhodopseudomonads, chromatis and others were seen. The following nonphotosynthetic bacteria were identified: Nocardia sp., three types of spirilli, two types of Spirochaeta sp., two types of Desulfovibria sp., a new strain of red Beneckea and four distinctive unidentified coccoid and filamentous bacteria. Reasons are given for believing several of the species are new to science and that the microbial diversity is far greater than the approximately twenty species reported here. Eukaryotes are extremely rare. Only one species of animal, a herpachtechoid copepod, was ever seen in the 8-km long microbial communities of the hypersaline basin. Dunaliella salina, a chlorophyte and Aspergillus sydowi, an ascomycetous fungus were the only eukaryotes that were observed to be regular components of mat communities. Ciliates, amoebae (including a chrysarchnion-like microbe) and diatom tests, mostly empty, were the only other eukaryotes observed. Attempts to enrich for eukaryotic microorganisms were not successful whereas attempts to enrich for bacteria, especially anaerobes led to such a profusion of forms that to continue detailed study of them was beyond our means. Unidentified small rods and cocci constituted the largest fraction of individuals in the subsurface community. The microbes isolated from mats are adapted for alternating dry and wet conditions as well as high concentrations of salt and low concentrations of oxygen.

Biological Remnants in a Precambrian Sediment

A billion-year-old shale from the Nonesuch formation at White Pine Mine, Michigan, contains microfossils, porphyrins, and optically active alkanes. Pristane and phytane, which are isoprenoid hydrocarbons found in living plants and animals, are constituents of the ancient alkanes in the Nonesuch shale; the presence of porphyrins in this Precambrian sediment suggests that photosynthetic organisms have existed for more than a billion years.