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Schopf, J. W.

Publications and source records attributed to Schopf, J. W..

33 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

The development and diversification of Precambrian life

The temporal relationships among various prominent events occurring in the evolution of life are considered. It is seen that the Precambrian encompasses an enormous segment of geologic time and includes more than 80% of the history of life on this planet. As a result of the studies of the past decade it appears that living systems were probably extant as early as 3300 m.y. ago. Photoautotrophs, apparently including blue-green algae, originated earlier than 3000 m.y. ago. Blue-green algae were the dominant components of earth's biota for the period extending from about 3000 to 1000 m.y. ago. The nucleated, eukaryotic cell type had become established at least as early as 900, and possibly prior to 1300 m.y. ago.

Schopf, J. W.↗
NASA NTRS1972

Carbon isotopic studies of organic matter in Precambrian rocks.

A survey has been undertaken of the carbon composition of the total organic fraction of a suite of Precambrian sediments to detect isotopic trends possibly correlative with early evolutionary events. Early Precambrian cherts of the Fig Tree and upper and middle Onverwacht groups of South Africa were examined for this purpose. Reduced carbon in these cherts was found to be isotopically similar to photosynthetically produced organic matter of younger geological age. Reduced carbon in lower Onverwacht cherts was found to be anomalously heavy; it is suggested that this discontinuity may reflect a major event in biological evolution.

Oehler, D. Z.↗
NASA NTRS1972

Precambrian paleobiology.

Outline in broad terms of major events in Precambrian biological history. Limitations of the Precambrian fossil record, chemical fossils, and findings of the early, middle, and late Precambrian records are examined. Biological systems originated during the earliest third of geologic time, about four billion years ago. It is generally assumed that the primitive atmosphere was a highly reduced mixture, primarily composed of methane and ammonia, and that the earliest living systems were heterotrophic, using organic matter of abiotic origin as a carbon source. The development of the metazoan grade of organization apparently occurred near the close of the Precambrian. The picture of gradually accelerating early evolutionary development, beginning rather slowly but markedly quickening with the emergence of eucaryotic organization, seems consistent with the fragmentary evidence currently available.

Schopf, J. W.↗
NASA NTRS1971

Artificial microfossils - Experimental studies of permineralization of blue-green algae in silica.

A technique has been developed to artificially fossilize microscopic algae in crystalline silica under conditions of moderately elevated temperature and pressure. The technique is designed to simulate geochemical processes thought to have resulted in the preservation of organic microfossils in Precambrian bedded cherts. In degree of preservation and mineralogic setting, the artificially permineralized microorganisms are comparable to naturally occurring fossil algae.

Oehler, J. H.↗