数百万年前の致命的な気候変動は火山噴火によるものであったと科学者らが結論。(Lethal Climate Change Millions of Years Ago Was Due to Volcanic Eruptions, Scientists Conclude)

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2023-10-09 ニューヨーク大学 (NYU)

数百万年前の致命的な気候変動は火山噴火によるものであったと科学者らが結論。(Lethal Climate Change Millions of Years Ago Was Due to Volcanic Eruptions, Scientists Conclude)
Photo credit: frantic00/Getty Images

◆過去2億6000万年間の気候変動は、大規模な火山噴火とそれに続く環境危機によって引き起こされ、生命の大量絶滅をもたらしたと科学者チームが結論づけました。
◆火山噴火が大気に大量の二酸化炭素を放出し、温室効果気候温暖化を引き起こしました。これらの現象は太陽系の軌道の変化と周期的に一致し、地球の気候に大きな影響を与えました。
◆ただし、これらの結論は現代の気候変動とは無関係で、それは人間活動によるものです。火山活動と気候のサイクルの関連性は、天文学的な周期とも共通しており、地球内部の地質学的プロセスに影響を与えています。

<関連情報>

過去2億6000万年間の大陸洪水玄武岩(CFB)、超熱気候パルス、無酸素海洋、および大量絶滅の相関エピソードにおける約32.5 Myと∼26.2 Myのサイクル: 地質学的サイクルと天文学的サイクルの関連性 Cycles of ∼32.5 My and ∼26.2 My in correlated episodes of continental flood basalts (CFBs), hyper-thermal climate pulses, anoxic oceans, and mass extinctions over the last 260 My: Connections between geological and astronomical cycles

Michael R. Rampino, Ken Caldeira, Sedelia Rodriguez
Earth-Science Reviews  Available online: 25 September 2023
DOI:https://doi.org/10.1016/j.earscirev.2023.104548

Abstract

Potential temporal and causal connections among various geologic events have long been discussed in the geological literature. More recently, signs of common periodicities in these episodes have been reported. In this study of correlation and cyclicity of geologic occurrences, we review and synthesize previous work, and utilize the newest data for various major events over the the last 260 My. These include, 1) high-quality radio-isotopic age determinations (U-Pb zircon and 40Ar/39Ar) for continental flood-basalt (CFB) eruptions; 2) the dates of widespread intervals of ocean anoxia; 3) the latest published dates of marine and non-marine extinction events, 4) hyper-thermal climate intervals and 5) the occurrences of stratigraphic Hg anomalies, and non-radiogenic Os-isotope anomalies as potential proxies for large-scale basaltic volcanism.

Times of at least 13 of 17 intervals of anoxic oceans are marked by stratigraphic Hg-anomalies, pointing to contemporaneous LIP eruptions, and 5 anoxic intervals in the warm Cretaceous Period are correlated with marine Os-isotope ratios suggesting potential LIP hydrothermal activity. Nine of the ocean-anoxic intervals are thus far correlated with times of marine-extinction episodes, and 8 of those anoxia/extinction co-events are significantly correlated with the ages of the well-dated CFB eruptions. Seven of the marine-extinction events and associated CFB volcanism are coeval with extinctions of non-marine vertebrates, supporting global catastrophic volcano-climatic episodes devastating both marine and terrestrial environments.

New digital circular spectral analyses revealed significant underlying cycles of ∼32.5 My and ∼ 26.2 My in the ages of the anoxic events and marine extinctions. Spectral analysis of the latest high-quality ages of the CFBs resulted in similar significant periodicities of 32.8 My and 12.9 My (∼26.2/2 My harmonic). High-frequency periods at various harmonics appear at ∼6.4 My, 8.4 My and 9.7 My in each of the three spectra.

These findings support a multi-factor extinction scenario in which release of massive amounts of CO2 and perhaps CH4 mostly from CFB magmas (and in some cases sub-volcanic intrusions into carbon-rich deposits), led to very warm climate intervals with near-lethal to lethal hyper-thermal conditions on land and in the sea. Concurrent release of halogens from CFB eruptions could also have decimated the global ozone layer. In many cases, the warm oceans became acidic, and developed anoxic to euxinic conditions, even up to the ocean surface, contributing to the causes of the marine extinctions. Additionally, four extinction events (late Eocene, end-Cretaceous, end-Jurassic and mid-Norian) correlate closely with the ages of the 4 largest impacts (craters ≥100 km in diameter) over the same period, capable of producing severe climatic effects and extinctions.

The potential dominant underlying ∼33-My and 26-My cycles, reported in these and other correlated tectonic, climatic, and biotic events over the last 260 My and beyond, are likely related to the Earth’s tectonic-volcanic rhythms, but the similarities with known Milankovitch Earth orbital periods and their amplitude modulations, and with known Galactic cycles, suggest that, contrary to conventional wisdom, the geological events and cycles may be paced by astronomical factors.

1702地球物理及び地球化学
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