Asteroid-impact hypothesis

A semi-quantitative asteroid impact hypothesis of tektite origin. J. Geophys. Res. 66, 2521 (1961). 

Four different ways of calculating the asteroid diameter all give a value of 10 km and this consistency lends confidence to the asteroid-impact theory. The Ir anomaly was first observed by us in Italian rock. Our theory predicted that the unusually abundant Ir should appear all over the world where the C-T boundary is exposed (intact). Part of the hypothesis was confirmed when the anomalously high Ir abundance was found in the C-T boundary layers in Denmark, northern and south-east Spain, and half-way round the world in New Zealand. Another prediction of the theory is that a component of the clay layer at the C-T boundary would be different in composition from other clays in the same section because it contained a component from the impact site. This prediction was confirmed in measurements of the Italian and Danish sections [1]. 

Asteroid- or Comet-Impact Hypothesis of Tektite Origin. In Tektites, J. A. O Keefe, Ed. Chicago, 1963. 

In 1979 geologist Walter Alvarez and his Nobel Prize-winning physicist father Luis Alvarez suggested that unusually high concentrations of iridium in rocks laid down at the K-T boundary meant that an asteroid had hit the earth, causing tremendous devastation. In the last 20 years much evidence has accumulated to support this hypothesis, including identification of the location of the probable crater caused by the impact in the ocean near Mexico. 

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