月の年齢:月面のサンプルのウラン・ソリウム・鉛系学的同位体研究
まとめ
アポロ11号の月面サンプルには,塵とブレッチアが含まれ,放射線年代測定を用いて,一致する年齢が46億6千万年であることを明らかにしています. この年齢は隕石と地球の年齢と一致し,初期の太陽系形成を示しています.
科学分野:
- 地質化学 地質化学
- 宇宙化学 (コスモケミストリー)
- ラジオメトリック・デッティング
背景:
- 月面サンプルを分析することで,初期の太陽系と惑星の形成に関する洞察が得られる.
- 月面の物質の年齢を理解することは,月と地球の時間的枠組みにとって極めて重要です.
研究 の 目的:
- アポロ11号の年齢を測定するために,放射線年代測定技術を用いて月のサンプルを採取した.
- 異なる月のサンプルタイプ (塵,ブレッチア,結晶岩) の年齢を比較し,太陽系年代表と関連付けます.
主な方法:
- ウラン (U),ソリウム (Th),鉛 (Pb) の同位体の放射線年代測定法.
- (207) Pb/(206) Pb, (206) Pb/(238) U, (207) Pb/(235) U,および (208) Pb/(232) Th. を含む同位体比の分析
- ウランイソトープ比の測定 ((238) U/(235) Uと (234) Uの均衡).
主要な成果:
- 研究されたアポロ11号のサンプルには,U,Th,Pbの低濃度が見つかりました.
- 微塵とブレッチャのサンプルの年齢は46億6千万年と一致しています.
- 6つの結晶と膀のサンプルでは,塵やブレッチアと比較して明らかに若い年齢を示した.
- 238U/235Uの比率は地上の岩石と一致しており,234Uは238Uと放射性均衡状態にあった.
結論:
- アポロ11号の塵とブレッチア (4,660億年) の年齢は,公認されている隕石と地球の年齢に匹敵します.
- これは,これらの月の物質が太陽系の歴史の初期に形成されたことを示唆しています.
- 結晶のサンプルの若い年齢は,後の地質学的な活動や月面での明確な形成イベントを示しています.
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