ИСТИНА

A relatively rapid metazoan diversification known since Charles Darwin (1859) as the “Sudden Appearance” or, nowadays, as the Cambrian Explosion took pace in two phases at least and embraced a relatively lengthy interval of over 30 million years. This process began from the very appearance and radiation of the first distinct skeletal metazoan species dominated mostly by stem groups at the end of the Ediacaran and the earliest Cambrian c. 545-530 million years ago (Ma), their following decline and extinction c. 513 Ma with a subsequent diversification of crown groups extending to the Ordovician Radiation. Integrated high-resolution isotope and elemental analyses of rocks yielding late Ediacaran – early Cambrian fossils, especially those of the Siberian Platform, revealed that these events occurred on the background of a highly unstable ocean composition including its oxygen and carbon dioxide contents, the magnesium to calcium ion ratio, phosphate and silica inputs among others which fluctuated in concert with the animal diversification phases. These drastic changes were influential for the fates of the evolution of different groups but, at the same time, the evolving organisms step by step took over abiotic process in maintaining a number of principal marine elemental cycles (calcium, phosphate, silica) as well as in the ocean oxygenation through coupling carbon and sulphur cycles and, probably, on the carbon dioxide output through carbonate sedimentation.