Ganapathy R
Science. 1980 Aug 22;209(4459):921-3. doi: 10.1126/science.209.4459.921.
Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the "fish clay" from Denmark representing the Cretaceous-Tertiary boundary. Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of 10(4) to 10(2) relative to cosmic abundances, are enriched in this boundary clay by factors of 5 to 100 over the expected abundances. With the exception of rhenium, all the enriched noble metals in the clay are present in cosmic proportions, indicating that the impacting celestial body had not undergone gross chemical differentiation. The major extinction of life on the earth at the end of the Cretaceous Period may be related to the meteorite impact.
代表白垩纪-第三纪界限的丹麦“鱼黏土”中存在陨星碎片，这表明6500万年前曾有一颗大型陨星撞击地球。贵金属（铱、锇、金、铂、铼、钌、钯、镍和钴）是陨星的敏感指示物，相对于宇宙丰度，它们在地球表面通常会减少10⁴到10²倍，而在这条界限黏土中，它们的含量比预期丰度高出5到100倍。除铼之外，黏土中所有富集的贵金属都以宇宙比例存在，这表明撞击天体并未经历过显著的化学分化。白垩纪末期地球上生命的大灭绝可能与陨星撞击有关。
