まとめ
6500万年前の小惑星の衝突がクレタセウス-第3期絶滅の原因になった可能性が高い. この衝撃は,世界中の堆積物で発見された高レベルのイリジウムを説明し,地球外衝突仮説を支持しています.
科学分野:
- 地質化学 地質化学
- パレオントロジー・パレオントロジー
- 惑星科学は惑星科学である.
背景:
- イリジウムのようなプラチナ群の元素は,地殻では稀である.
- 深海の堆積物におけるイリジウム濃度の上昇は,地球外からの物質の流入を示唆している.
- 6500万年前,白紀-三次紀 (K-T) の境界線は,大量絶滅のイベントをマークしています.
研究 の 目的:
- K-T境界におけるイリジウム異常の起源を調査する.
- 小惑星の衝突がK-T絶滅を引き起こしたという仮説を検証するために.
- 地球外物質の流入と大量絶滅の出来事を相関させるため.
主な方法:
- イタリア,デンマーク,ニュージーランドからの深海の石灰岩堆積物におけるイリジウム濃度の分析.
- K-T境界におけるイリジウム濃度と背景濃度の比較.
- 境界粘土と周辺の石灰岩層の化学分析.
主要な成果:
- 重要なイリジウム増加 (30-160倍の背景値) は,K-T境界で複数の場所で見つかりました.
- イリジウムは超新星からではなく,地外からの起源であると確認されています.
- 境界性粘土の組成は,白紀と三次紀の石灰岩と著しく異なっており,塵から派生した起源を支持しています.
結論:
- 大きな小惑星の衝突 (推定直径10 +/- 4 km) が,K-T絶滅の最も妥当な原因である.
- 衝突により,膨大な量の塵が平流層に注入され,地球規模で暗闇を引き起こし,光合成が抑制されました.
- このメカニズムは,大量絶滅の古生物学的証拠と地化学的発見と一致しています.
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