Note on possible reason for scarcity of calcareous skeletons of invertebrates in Precambrian formations

It is suggested that it was not the lack of calcium carbonate in Precambrian seas, but the high Mg/Ca ratio in those sea waters which prevented the formation of hard protective and skeletal structures of organisms or largely hindered this formation.

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				J. W. Cowie Life in Pre-Cambrian and early Cambrian times Geological Society, London, Special Publications, January 1, 1967; 2(1): 17 - 35. [Abstract] [PDF]