本文认为重力分异作用是地球中钙、镁元素发生径向迁移的动力。据此,试探性地分析了早元古代时的海洋化学条件,并结合地球气圈和水圈的演化规律,论证了元古代是形成沉积型菱镁矿床最合适的时代。同时,相应解释了在地质史中,自元古代以来,富镁碳酸盐沉积逐渐变少、而富钙碳酸盐沉积逐渐变多这样一个全球性的基本地质事实。 This paper argues that gravity differentiation is the driving force for the radial migration of calcium and magnesium in the earth. Based on this, tentatively analyzing the marine chemical conditions during the Early Proterozoic, combined with the evolution of the Earth’s balloon and hydrosphere, it proves that the Proterozoic was the most suitable period for the formation of sedimentary magnesite deposits. At the same time, correspondingly, a basic global geological fact has been explained in the history of geology since the Yuan dynasty, the deposition of Mg-rich carbonate gradually decreases and the deposition of Ca-rich carbonate gradually increases.