Does the Earth have a pulse? Evidence relating to a potential underlying ~26–36-million-year rhythm in interrelated geologic, biologic, and astrophysical events

Abstract

ABSTRACT The existence of an ~26–36 m.y. rhythm in interrelated global tectonism, sea-level oscillations, climate, and resulting sedimentation patterns during Phanerozoic time (the last 541 m.y.) has long been suspected. A similar underlying ~26.4–27.5 m.y. cycle was reported independently in episodes of extinctions of marine and non-marine species. Subsequent spectral analyses of individual geologic events of the last 260 m.y., including changes in seafloor spreading and subduction, times of hotspot initiation and intraplate volcanism, eruptions of Large Igneous Provinces (LIPs), tectonic events, sea-level fluctuations, oceanic anoxia, atmospheric carbon dioxide levels, and global climate have revealed evidence for the 26–36 m.y. cycle and the temporal association of events with an apparent overall periodicity of ~27.5 m.y. modulated by an ~8–9 m.y. cycle. The proposed episodes of geologic activity and environmental and biotic change may result from cyclical internal Earth processes that affect changes in mantle convection, plate motions, intraplate stresses, and/or periodic pulses of mantle-plume activity. Recently, the ~30 m.y. cycle has been linked to Earth’s long-term orbital changes within the Solar System, and it may also affect tectonism and climate. I also note considerable evidence for a similar ~30 m.y. cycle in the ages of terrestrial impact craters, which suggests possible astronomical connections. The shared geologic cycle time, formally ranging from ~26 to 36 m.y. (depending partly on varying data sets, geologic timescales, and statistical techniques utilized) is close to the estimated interval (~32 ± 3 m.y.) between our cyclical crossings of the crowded mid-plane region of the Milky Way Galaxy. Here I outline a proposed astrophysical pacing for the apparent pulses of both impact cratering and rhythmic geological episodes.