Astronomical cycles as pacemakers of geological age boundary events

2022 Fiscal Year Final Research Report

• Project/Area Number: 19H02012
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17050:Biogeosciences-related
• Research Institution: The University of Tokyo
• Principal Investigator: IKEDA MASAYUKI 東京大学, 大学院理学系研究科(理学部), 准教授 (10635882)
• Co-Investigator(Kenkyū-buntansha): 堀 利栄 愛媛大学, 理工学研究科(理学系), 教授 (30263924) ; 後藤 孝介 国立研究開発法人産業技術総合研究所, 地質調査総合センター, 主任研究員 (30612171) ; LEGRAND Julien 静岡大学, 理学部, 助教 (60737534)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 地質時代境界事変 / 天文周期 / 絶滅 / 海洋無酸素事変 / ミランコビッチサイクル

Outline of Final Research Achievements

We examined mainly geochemical and palaeontological investigations across the Cenozoic and Mesozoic geological age boundaries in order to test the possibility that some of the indicative fossil occurrences and extinctions defined as geological age boundaries were pace-marked by astronomical cycles of environmental change. The results show that the 1-10 million year scale amplitude modulation cycle of the 20,000-100,000 year Earth orbital element change, which was the focus of the previous Milankovitch hypothesis, affected some of the climate changes at the geological age boundary via the monsoon and carbon cycle. The study also showed that the 10-million-year climate change may have affected biological evolution, including the early dispersal and enlargement of dinosaurs and other animals.

Free Research Field

古気候学

Academic Significance and Societal Importance of the Research Achievements

本研究は生物の絶滅や進化がどのように起きてきたかという謎への答えの一助として、巨大天体衝突や大規模火成活動だけでなく、地球軌道要素の極端な変化が重要であった可能性を指摘した。特に、日射量変動が植生や風化のフィードバックを介して、大気中二酸化炭素濃度を大きく変化させ、これが植物や恐竜などの脊椎動物、海洋無脊椎動物の群集変化やサイズ変化にも影響を与えていた点で、学術的および社会的な意義が高い