STAGES OF DEVELOPMENT OF THE EXTERNAL GEOSPHERES AND FORMATION OF SEDIMENTARY ROCKS IN THE HISTORY OF THE EARTH

Abstract

An analysis of the irreversible evolution of sedimentation throughout the history of the earth based on a hypothetical interpretation of the geochemical variation of the atmosphere and hydrosphere with time. During the primary (Azoic) stage of development of the earth it is envisioned that the composition of the hydrosphere and atmosphere were largely determined by the gases given off by the process of degasification of the mantle resulting in a highly acidic hydrosphere (HCl, HF, H3B03 and Si02) and an atmosphere consisting largely of CO2 with small amounts of water vapor, ammonia, methane, etc. Toward the end of the primary period, acid oceanic waters were converted to chloride-type waters. During the second stage of development (Archean) the crust of the earth was differentiated into the continental- and oceanic-type structural units which persisted throughout the remainder of earth history, Great amounts of carbonates resulting from the erosion of continental areas were carried into the seas, and the oceans were gradually transformed from chloride to chloride-carbonate type. The third stage of development (Proterozoic-Riphean) began with the emergence of photosynthesis resulting in the appearance of free oxygen in the atmosphere and hydrosphere. Toward the end of the Proterozoic the atmosphere attained essentially its present composition. Changes in sedimentary rock types reflect changes in the atmosphere and hydrosphere with a change from ferrous to ferrous-ferric iron deposits and the deposition of calcite instead of dolomite which had been precipitated extensively in Archean and earlier Proterozoic time. The most recent stage of development (Historic) is characterized by the increase in O2 content of the atmosphere and the rapid expansion of living organisms. Sea water also changed from a chloride- carbonate-sulfate type in the Proterozoic, to a chloride-sulfate type in the Historic period. Deposition during the latest stage of chemogenic earth development reflects the changes in atmosphere and hydrosphere, with extensive carbonaceous-carbonate-halide sediments. Factors causing the complex geochemical evolution throughout earth history were: the rock-forming process, the development of life, and the tectonic development of the crust. H. C. Kent