大气圈和水圈物质组成的演化及其对表生地质作用的制约

EVOLUTION OF THE EARTH′S ATMOSPHERE AND HYDROSPHERE AND ITS EFFECTS ON SUPERGENIC GEOLOGICAL PROCESSES

地球的大气圈、水圈的形成在太阳系中具有独特性。大气圈、水圈的物质组成呈现阶段性的演化特征。在不同的演化阶段 ,地球表生地质作用表现出不同的特征和状况 ,显示出地球大气圈、水圈化学变化对其的控制作用。在长时间尺度范围内 ,大气和海洋化学变化直接影响表生系统的岩石风化强度和特点、沉积物类型、矿产时空分布规律 ;在短时间尺度范围内 ,大气物质组成的变化引起气候变化 ,间接地、综合地影响和改变表生地质作用的状况。同时 ,表生地质作用反过来又影响大气圈、水圈的物质组成演化 ,两者相互作用 ,相互影响 ,构成地球表生系统的相互耦合关系。

The evolution of the Earth′s atmosphere and hydrosphere is divided into 5 stages. In corresponding stage, the supergenic geological processes were different from each other. The early Archean, 4.6～3.8Ga ago, was prevailed by intense degassing which give rise to an atmosphere of condensed volcanic gases with H 2O and CO 2. There are no water in superficial environment at that time. With the cooling down of the Earth, the hydrosphere appeared at 3.8Ga ago as the volcanic atmosphere evolved into a CO 2 atmosphere. The prime ocean, strongly acidic reducing, attained a great lot of cations from the weathering of the continent rock, however, only a fraction of them were precipitated, others were dissolved in seawater as chloride. The seawater pH raised as the result of intensification of the strength of rock weathering. At 2.6Ga ago, the first carbonate strata was precipitated from the seawater, and from then on, CO 2 was transferred in increasing quantity to the seawater and carbonate rock. Between 2.6 and 1.8Ga ago, the content of CO 2 in atmosphere decreased periodically, the content of N 2 increased gradually, and a few of O 2 appeared. The seawater was of weakly acidic and reducing state. Because of longer quiescent interval of volcanism, the seawater pH were therefore retained at a higher level with weakly oxidizing, the atmosphere was in weakly oxidizing state too. Being in the stage of 1.8～0.6Ga ago, the terrestrial environment were different, with red bed, oolitic iron ore, and thick carbonate strata were formed while banded Fe Si formations disappeared, due to impede on Fe transporting into ocean by continental weathering. With further consumption of Earth′s internal energy since Cambrian (0.6Ga ago), the atmosphere had evolved into a O 2 and N 2 dominated atmosphere from a CO 2 dominated one, the seawater was in the weakly alkaline strongly oxidization state in which the chemical precipitation was weakening. It is worthwhile to point out that the evolution of chemical composition of atmosphere and hydrosphere affected directly the supergenic environment which influenced reversely on the atmosphere and hydrosphere on a long time scale.$$$$