Marine regression occurred when the main seas on Earth started to drain. It is believed to have begun before the KT period. Estimates of marine regression state that about eleven and a fifth million square miles of land were exposed from the draining of the oceans. This massive land addition to the environ

The most accepted theory that explains the extinction of the dinosaurs is the asteroid impact theory. In 1979, Luis Alvarez and his son Walter Alvarez hypothesized that a bolide, a comet or asteroid, over ten kilometers in diameter crashed into Earth. This bolide created widespread disasters such as wildfires, global darkness, climate changes, and acid rain which led to a global catastrophe wiping out many plants and vertebrate species including the dinosaurs. The evidence supporting the asteroid impact lies in the high concentration of iridium and shocked quartz in the Chicxulub crater, which is the believed site where the giant bolide landed. Both iridium and shocked quartz are quite rare and uncommon on Earth. Iridium is not normally present on Earth except as the result of meteorite impact on Earth. Shocked quartz is only found on Earth from nuclear test sites and near impact craters. The fact that both iridium and shocked quartz has been found in many meterite sites around the world during the KT boundary strongly supports the asteroid impact theory.

Volcanism refers to the massive eruption of flood basalts which disrupted the ecosystem of Earth. These flood basalts were known as the Deccan Traps, which cover a large part of India and Pakistan. Massive eruptions were thought to have taken place in intervals from up to five-hundred thousand years before the KT boundary with shorter intervals between eruptions closer to the KT boundary. These gigantic eruptions coincide with the magnetic pole reversal which is believed to have happened around the KT boundary; however, there is no concrete connection between the reversal of the magnetic poles and extinction. According to Vincent Courtillot, “…the most extensive individual flows in the sequence may cover almost 4,000 square miles with volumes exceeding 2,400 cubic miles….He suggests that the flows originally may have covered almost 800,000 square miles, with a volume possibly exceeding 350,000 cubic miles” (Archibald, 1996). The lava that spread throughout modern day India and Pakistan created an excess of carbon dioxide in the atmosphere. This increase in carbon dioxide would have created a bigger boom for plants as well as sped up the process of global warming. Both of these effects are contradictory to evidence of the environment after the KT boundary. The climate on Earth cooled, and plants were rapidly disappearing according to the geological record. Another problem with the volcanism theory is that it is too narrow, and it does not explain the extinction of other species besides dinosaurs. Volcanism merely states that the cool climate created from lava flow would have increased difficulties in survival through lack of adaptation. The massive lava flows also contained a highly toxic element called selenium, which was found in the shells of dinosaur eggs in the KT boundary. So, volcanism accounts for the extinction of dinosaurs, but it is too narrow in the sense that it does not account for any other vertebrate species or plants.

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Some topics in this essay:
, South America, India Pakistan, Yucatan Peninsula, Science Weekly, North America, Walter Alvarez, Cretaceous” Monastersky, Earth Shocked, Montana KT, asteroid impact, kt boundary, asteroid impact theory, impact theory, marine regression, fossil record, hell creek, vertebrate animals, plants vertebrate, global catastrophe, shocked quartz, hell creek formation, iridium shocked quartz, plants vertebrate animals, marine regression volcanism,