イリジウムの豊富さはオルドヴィシアン-シルウリアン層型にまたがる
Science (New York, N.Y.)
|July 18, 1986
まとめ
スコットランドのオルドビキア紀・シルウリア紀の境界シェールにおける高濃度のイリジウムは,絶滅の出来事と相関していない. 地球外からの衝突ではなく,地球上の超大質量岩の侵食が,これらの持続的なイリジウムレベルを説明している可能性が高い.
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
- ストラティグラフィー ストラティグラフィー
背景:
- オルドビキウス・シルウリアン間の境界線は,重要な絶滅の出来事を示しています.
- イリジウムの異常は,しばしば地球外からの衝突と関連付けられています.
- スコットランドのドブズ・リン (Dob's Linn) は,オルドヴィキウス・シルウリウス境界の重要な層型断面である.
研究 の 目的:
- ドブス・リンのオルドビキウス・シルウリアン境界を越えたイリジウムの濃度を調査するために.
- グラプトリチスシェール部分における高濃度のイリジウムの源を特定するために.
- イリジウム濃度と主要な絶滅の出来事との関係を評価する.
主な方法:
- ドブス・リンセクションから採取したシェールサンプルの化学ストラトグラフィック分析.
- イリジウムとクロムの濃度の測定.
- 源地エリアの古地理学的および地質学的再構築.
主要な成果:
- 継続的に高濃度のイリジウム (0.0500.250ppb) は,検査された境界区間全体と13のグラプトライトゾーンを取り囲む中で発見されました.
- 大規模な絶滅の出来事にもかかわらず,境界線または他の場所でイリジウム濃度の急上昇は検出されなかった.
- イリジウムの濃度はクロムと相関しており,シルル紀下期の段階的な減少を示しており,クロムとイリジウムの比率は平均106.6である.
結論:
- 高度で持続的なイリジウムの濃度は,露出した上層マントルの超岩の陸上侵食に起因する.
- この発見は,高レベルのイリジウムの原因として,大災害的な地球外の出来事を支持しません.
- この研究は,堆積物のシーケンス内の地化学的異常における地上のプロセスの重要性を強調している.
関連する概念動画
01:21Layers of the Epidermis
The epidermis, the outermost layer of the skin, is composed of several distinct layers. From deep to superficial, the layers of the epidermis are as follows:
Stratum Basale
Stratum basale, also known as the stratum germinativum, is the deepest layer of the epidermis. It is composed of a single layer of actively dividing cells called basal cells or basal keratinocytes. These cells constantly undergo cell division to replenish the upper layers of the epidermis. Additionally, melanocytes, which...
Stratum Basale
Stratum basale, also known as the stratum germinativum, is the deepest layer of the epidermis. It is composed of a single layer of actively dividing cells called basal cells or basal keratinocytes. These cells constantly undergo cell division to replenish the upper layers of the epidermis. Additionally, melanocytes, which...
01:15Reticular Dermis
The papillary and reticular dermis are the two layers of the dermis. They are made of connective tissue with fibers of collagen extending from one to the other, making the border between the two somewhat indistinct. The dermal papillae extending into the epidermis belong to the papillary layer, whereas the dense collagen fiber bundles below belong to the reticular layer.
Reticular Layer
Underlying the papillary layer is the much thicker reticular layer, composed of dense, irregular connective...
Reticular Layer
Underlying the papillary layer is the much thicker reticular layer, composed of dense, irregular connective...
01:20Region of Convergence of Laplace Tarnsform
The Region of Convergence (ROC) is a fundamental concept in signal processing and system analysis, particularly associated with the Laplace transform. The ROC represents an area in the complex plane where the Laplace transform of a given signal converges, determining the transform's applicability and utility.
Consider a decaying exponential signal that begins at a specific time. When deriving its Laplace transform, the time-domain variable is replaced with a complex variable. This substitution...
Consider a decaying exponential signal that begins at a specific time. When deriving its Laplace transform, the time-domain variable is replaced with a complex variable. This substitution...
01:12Maximum Size of Aggregate
The maximum size of aggregate is defined as the aperture of the sieve retaining 15 percent or more of the particles present in the aggregate sample. The aggregate's maximum size impacts the concrete's water requirement, workability, and strength. Larger aggregates reduce the surface area needing cement paste coverage, which can lower water needs, thereby allowing a decrease in the water-to-cement ratio when the desired workability and richness of the mix are to be maintained, which can result...
01:27Energy Line and Hydraulic Gradient Line
Based on Bernoulli's equation, the energy line (EL) and hydraulic grade line (HGL) provide graphical representations of energy distribution in a fluid flow system. For steady, incompressible, inviscid flows, Bernoulli's equation is expressed as:
01:18Boundary Layer Characteristics
When a fluid encounters a solid surface, a boundary layer forms due to the interaction between the fluid's motion and the stationary surface. This phenomenon is characterized by a thin region adjacent to the surface where viscous forces dominate, influencing the fluid's velocity profile. The development of the boundary layer begins at the leading edge of the surface and evolves as the fluid moves downstream.As the fluid flows over the surface, friction between the fluid and the wall slows down...