Mobilization of the Platinum Group Elements by Low-temperature Fluids: Implications for Mineralization and the Iridium Controversy

may have been • mantle plume, but, alternatively, it may have been triggered by an asteroidal impact An impact fall-out layer with shocked debris has been reported at the Tr/J boundary in Italy [13]. The s ynchronicity of extrusion and extinction appear established as an event horizon independent of radiometric or fossil stratigraphy. Of course, enthusiasm for impacts does not score points in the scientific forum, but the current evidence of their importance in shaping other terrestrial planets (Venus has 900 impact craters as well as 1500 volcanos) suggests that impacts need not be assigned a role of last resort. References: [1] Dietz (1964) /. Geol.. 72.412-434. [2] Dietz