Direction: sketch the outline of the passage. There is little doubt that something of catastrophic proportions had to have occurred to wipe out the dinosaurs 65 million years ago. However, there is considerable controversy over what might cause this event, which is commonly known as the Cretaceous-Tertiary (K-T) extinction. The two most widely accepted explanations of the extinction event are the asteroid impact theory and the volcano-greenhouse theory. Nobel-prizewinning physicist Lius Alvarez, and his son, Walter, were the first to propose the asteroid impact theory in 1980. They postulated that a huge asteroid, approximately 10 kilometers in diameter, crossed into the Earth’s atmosphere and slammed into its surface, emitting a heat wave that incinerated everything within a large radius. It would also have triggered a variety of disasters including massive fire, volcanic eruptions, tsunami and severe storms. Debris and dust would have been scattered widely, changing the chemical makeup of atmosphere and blocking out sunlight at least a few months. The aftermath of asteroid impact paints a grim picture, with many life forms, including the once mighty dinosaurs, unable to adapt to new conditions. Oxygen levels would have dramatically decreased, killing many land and ocean species. Plants would have wilted away, having no sunlight to generate photosynthesis for their nourishment, and without plants, the animals dependent on them for sustenance would also perish due to starvation. The second theory for the extinction of dinosaurs was offered by scientist Dewey Mclean. The Volcano Greenhouse Gas theory claims massive volcanic eruptions from the volatile Deccan traps, an igneous region of India, were what caused the K-T extinction event. Mclean’s theory was based on the discovery of lava flows from the Deccan traps at geological K-T boundary, which have been dated to approximately 65 million years ago. According to Mclean’s theory, intense volcanic activity filled the atmosphere with unprecedented quantities of carbon dioxide, leading to an extreme greenhouse effect. This would have caused eggs and vulnerable embryos to overheat and die and made species sterile. Plankton in the sea would have been killed, disrupting the important food chain that all animals need to survive. Moreover, the lack of oxygen would have suffocated many animals, causing them to die out.