The evolution of Earth's surficial Mg cycle over the past 2 billion years.

The hinge points for the δ 26 Mg sw curve are sparser in the Proterozoic, particularly before 800 Ma, but they reveal an increasing trend of δ 26 Mg sw with increasing age, from −0.2 ± 0.2‰ during the Neoproterozoic, to 0 ± 0.2‰ during the Mesoproterozoic, to ≥ +0.5‰ in the early Paleoproterozoic ( Fig. 1B ).

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