生命起源、早期演化阶段与海洋环境演变

近年的研究表明，地球生命可能起源于距今39~36亿年之间。除了碳元素以外，水、氮、氢、磷等元素也是生命起源的必备条件，黏土矿物和金属硫化物是有机质合成的重要催化剂，有热液活动的碱性热水环境是最有利生命发生的孵化场。自原核生物在约3.5 Ga出现之后，生命就一直表现为与环境的协同进化关系。大气圈氧化是地球史上最重大的地质事件之一，它不仅改变了地球表层环境条件、加速了表生地质过程和新矿物的产生，而且改变了海洋化学条件和元素循环。大气圈氧化事件的根本在于产氧蓝细菌的出现，元古宙中期海洋化学性质的整体转换也与微生物过程密切相关。新元古代多细胞生物的繁盛和末期后生动物的出现及其在寒武纪初期的快速多样化是生物圈演化的重大飞跃。这个过程也与海洋氧化增强及其导致的海洋化学变化密切相关，其中硫化水域消失和减弱以及海水中微营养元素可得性增加可能是重要因素，这也与微生物过程直接相关。

Life origin,early evolution stages,and ocean environment changes

Increasing evidence suggests that life most likely originated in a time between ca 3.9 and 3.6 Ga on the earth, with the earliest recognizable fossils recorded in the rocks of ca 3.5 Ga. Besides carbon, water, nitrogen, hydrogen, and phosphorous are indispensable chemical elements, while clay minerals and metal sulfides are key catalysts for organic synthesis. Early environments with saline water and hydrothermal activity seem to be the most favorable hatch pool for the origin of life. Since prokaryotic organisms emerged not later than ~3.5 Ga, biosphere as an important geologic agent interacting with atmosphere ocean has greatly accelerated the evolution of Earth surface systems, showing an apparent co evolution with environments. As one of the most important events in Earth history, the Great Oxygenation Event (GOE) has not only altered the earth surface environments profoundly, accelerated various geologic processes and the generation of new minerals, but also reset the ocean chemistry and element cycles. GOE resulted virtually from the onset of oxygen producing photosynthesis, and the overall transition of ocean chemistry at ca 1.8 Ga was also closely related to microbial processes. The emergence of metazoans at the terminal Neoproterozoic and their rapid diversification at the beginning of the Phanerozoic are significant innovations in life evolution. These innovations are closely linked to the further increase of atmospheric oxygenation and the consequent changes in ocean chemistry at the times, particularly to the shrinkage of euxinic waters and the increasing availability of bio essential elements in seawater, in which microbes always play essential roles.