| Popis: |
This study examines the history of the paradigm concerning a lunar (or solar-system-wide) terminal cataclysm (also called “Late Heavy Bombardment” or LHB), a putative, brief spike in impacts at ~3.9 Ga ago, preceded by low impact rates. We examine origin of the ideas, why they were accepted, and why the ideas are currently being seriously revised, if not abandoned. The paper is divided into the following sections: Overview of paradigm. Pre-Apollo views (1949−1969). Initial suggestions of cataclysm (ca. 1974). Ironies. Alternative suggestions, megaregolith evolution (1970s). Impact melt rocks “establish” cataclysm (1990). Imbrium redux (ca. 1998). Impact melt clasts (early 2000s). Dating of front-side lunar basins? Dynamical models “explain” the cataclysm (c. 2000s). Asteroids as a test case. Impact melts predating 4.0 Ga ago (ca. 2008−present.). Biological issues. Growing doubts (ca. 1994−2014). Evolving Dynamical Models (ca. 2001−present). Connections to lunar origin. Dismantling the paradigm (2015−2018). “Megaregolith Evolution Model” for explaining the data. Conclusions and new directions for future work. |
