The start of the Mesozoic Era is marked by roughly 5 m.y. of Earth system upheavals, including unstable biotic recovery, repeated global warming, ocean anoxia, and perturbations in the global carbon cycle. Intervals between crises were comparably hospitable to life. The causes of these upheavals are unknown, but are thought to be linked to recurrent Siberian volcanism. Here, two marine sedimentary successions at Chaohu and Daxiakou (South China) are evaluated for paleoclimate change from astronomical forcing. In these sections, gamma-ray variations indicative of terrestrial weathering reveal enhanced obliquity cycling over prolonged intervals, characterized by a 32.8 k.y. periodicity with strong 1.2 m.y. modulations. These suggest a 22 h length of day and 1.2 m.y. interaction between the orbital inclinations of Earth and Mars. Comparing the 1.2 m.y. obliquity modulation cycles in these sections with Early Triassic records of global sea level, temperature, redox, and biotic evolution suggests that long-term astronomical forcing was involved in the repeated climatic and biotic upheavals that took place throughout the Early Triassic.
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