The Cretaceous-Tertiary Impact Theory

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Introduction The Cretaceous- Tertiary extinction event was one of the largest mass extinctions ever recorded on Earth. Occurring 65 million years ago, this cataclysmic event marked the extinction of thousands of animal species including dinosaurs, mosasaurs, plesiosaurs, and pterosaurs. Dramatic extinctions also occurred among microscopic floating organisms; both calcareous plankton and calcareous nanoplankton were nearly exterminated with only a few species surviving (Alvarez et al. 1980). Alternatively, some groups were little affected, including the terrestrial plants, crocodiles, snakes, mammals, and many kinds of invertebrates. It is estimated that a little over half of all living species present at the end of the Cretaceous did not survive the mass extinction (Russell 1979). A dark grey clay sediment layer 3-8 centimeters thick divides the end of the Cretaceous period and the beginning of the Tertiary, this layer is referred to as the K-T boundary and is found nearly globally (K is the traditional abbreviation for the Cretaceous Period, and T is the abbreviation for the Tertiary Period). For years the scientific community debated the cause the extinction; many hypotheses, such as massive volcanic eruptions, excessive solar radiation and others, were presented but they lacked the proper supporting evidence. Finally, beginning in the 1980’s through until the early 1990’s several prominent researchers including Luis Alvarez, Bruce Bohor, and Alan Hildebrand began to present significant proof that an asteroid impact caused the Cretaceous-Tertiary (K-T) mass extinction. In this paper we will discuss the Cretaceous-Tertiary Impact theory and look at the important pieces of evidence supporting it, including the high levels of iridium and shocked quartz in the K-T layers, as well as the Chicxulub Crater in southern Mexico. Iridium concentrations Iridium is

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