(40) Ar/(39) Arから月の衝突の歴史 dating of glass spherules ガラス球体の年代測定
1Department of Geology and Geophysics, Department of Physics, University of California, Berkeley, CA 94720, USA. Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, U.
まとめ
月球球面の分析により,衝突クレーターの発生率は35億年以上にわたって変動していたことが明らかになった. 最近の月面衝突の増加は,地球との相関関係にある.
科学分野:
- 月面地質学とインパクトクレーター研究.
- 放射線年代測定と地球年代測定.
- 惑星科学と地球・月系進化.
背景:
- 月球球は,月面に隕石が衝突して形成されたガラス玉です.
- アルゴン-アルゴン (40Ar/39Ar) イソクロンテクニックは,これらの衝突イベントの日付を決定します.
- 月の衝突の歴史を理解することで,太陽系の進化の洞察が得られます.
研究 の 目的:
- アポロ14号からの月球球の年代分布を分析するために.
- 過去35億年の月のクレーター形成の速度を再構成する.
- 月面衝突の歴史と地球の生物学的進化の間の潜在的な相関を調査する.
主な方法:
- アポロ14号のレゴリット1グラムから月球球155個を分離した.
- アルゴン-アルゴン (40Ar/39Ar) イソクロン技術を用いた球球の年代測定.
- 衝突年齢の統計分析により,クレーター形成率の変動を決定する.
主要な成果:
- 月面のクレーター形成率は,過去35億年の間に2~3倍減少した.
- 最低クレーター形成率は5億~6億年前に観測されました.
- クレーター形成率は,過去4億年で3.7±1.2倍増加した.
結論:
- 月面の衝突流は恒定ではなく,大きな変動を示しています.
- 最近の月面衝突の増加は,地球上の急速な進化的放射線の時期と一致しています.
- 月面衝突と地上の生物学的変化の間の因果関係を確立するためにさらなる研究が必要である.
関連する概念動画
Constant Volume Calorimetry
Calorimeters are useful to determine the heat released or absorbed by a chemical reaction. Coffee cup calorimeters are designed to operate at constant (atmospheric) pressure and are convenient to measure heat flow (or enthalpy change) accompanying processes that occur in solution at constant pressure. A different type of calorimeter that operates at constant volume, colloquially known as a bomb calorimeter, is used to measure the energy produced by reactions that yield large amounts of heat and...
Radioactive Decay and Radiometric Dating
Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. The number of disintegrations per unit time is called the activity (A), which is directly proportional to the number of nuclei in the sample. The decay constant (λ) is an average probability of decay per nucleus in unit time.
Nuclear Transmutation
Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with another particle. The first manmade nucleus was produced in Ernest Rutherford’s laboratory in 1919 by a transmutation reaction, the bombardment of one type of nuclei with other nuclei or with neutrons. Rutherford bombarded nitrogen-14 atoms with high-speed α particles from a natural radioactive isotope of radium and observed protons being...
Impulse
According to Newton’s second law of motion, the rate of change of the momentum of an object is the net external force acting on it. The total change in momentum between two timepoints thus depends on both the external force acting on it and the time over which it acts. Describing this mathematically, the total change of an object’s motion is proportional to the force vector and the time over which it is applied. This product is called impulse.
Additionally, it can be shown that the total...
Additionally, it can be shown that the total...
Types of Collisions - II
When two or more objects collide with each other, they can stick together to form one single composite object (after collision). The total mass of the object after the collision is the sum of the masses of the original objects, and it moves with a velocity dictated by the conservation of momentum. Although the system's total momentum remains constant, the kinetic energy decreases, and thus such a collision is an inelastic collision. Most of the collisions between objects in daily life are...
Impact: Problem Solving
In an experiment conducted during a Mars mission, a rover propels a projectile with an initial velocity, and the projectile rebounds after colliding with the Martian surface. To ascertain the maximum height attained by the projectile after this collision, the known restitution coefficient and acceleration due to gravity are employed.
By designating the launch point as the origin and utilizing kinematic equations, the vertical component of the projectile's velocity at the point of impact is...
By designating the launch point as the origin and utilizing kinematic equations, the vertical component of the projectile's velocity at the point of impact is...


