While it is widely accepted that early animals originated and primarily evolved during the Neoproterozoic to
Cambrian period, there remains ongoing debate over how fluctuations in marine-atmospheric oxygen levels
influenced their evolution and diversification. To investigate this, we analyzed pristane/phytane ratios—a redoxproxy
based on organic geochemistry—in surface sediments from the Cryogenian to Cambrian successions in
South China, Oman, and Australia. The temporal changes in this proxy exhibited consistent patterns across all
sites, revealing five cycles of anoxic to oxic conditions in the ocean between 660 and 510 Ma. By examining the
average pristane/phytane ratios, we identified three events when oxygen levels increased. This represents a
transition from anoxic conditions to anoxic-dysoxic boundary at 630–600 Ma, followed by a shift to dysoxic
conditions at 570 Ma (Shuram event), and finally reaching oxic conditions at 520 Ma (Cambrian explosion).
Significantly, these oxygenation events align with eumetazoan evolution. An inverse relationship was observed
between oceanic redox events and positive/negative shifts of δ13Ccarb, occurring between the first and second
oxygenation events, suggesting an increase in atmospheric oxygen levels. Based on these findings, we propose
that there were global increases in oceanic and atmospheric oxygen levels, at least during the early Ediacaran
period. These shifts in oxygen levels likely played a role in influencing the rate of evolution among early animals.