"It's official: The extinction of the dinosaurs and a host of other species 65.5 million years ago was caused by a massive asteroid that crashed into the Gulf of Mexico..."
On March 4th, 2010, a group of internationally renowned scientists, who call themselves "the dream team", released to the public that the K-T boundary (Cretaceous-Tertiary boundary) mass extinction that occurred 65.5 million years ago completely resulted from a 7.5-mile-wide asteroid hitting the Earth. This asteroid, traveling at a speed 10 times that of a rifle bullet, released a billion times more energy than the Hiroshima atom bomb when it hit Earth. This collision caused wildfires, tsunamis, and earthquakes stronger than we've ever experienced, reaching up to an 11 or larger on the richter scale. Up until now, scientists have had many theories as to what caused this mass extinction, but they have now concluded that this asteroid was the direct cause of the extinction of half of the Earth's species 65.5 million years ago. The KT boundary extinction, also known as the greatest extinction in history, wiped out dinosaurs, early bird forms, large marine reptiles, and some smaller sea creatures. Following this extinction, mammals began to emerge and eventually dominated the planet.
Ever since the idea that the asteroid might be the cause of this extinction was proposed 30 years ago, "the dream team" members have been researching this extinction to prove it. How, after 30 years of speculation, did they finally settle on this theory? High concentrations of the element iridium in sediments from the K-T boundary are what finalized their belief in the asteroid being the cause of this extinction. Iridium is rarely found on Earth but abundant in space, and the age of these iridium filled sediment layers is the exact same age as the 1.5 mile deep crater in Mexico where the asteroid hit. Other theories based on multiple asteroid collisions or volcanic eruptions were eliminated. Scientists believe that if the mass extinction was caused be large volcanic eruptions, there would have been more activity in the biological world. The immediate cause of volcanism would have been global warming and prosperous biological diversity, but the exact opposite happened. The conclusion that a strong asteroid collision caused the largest extinction in history is finalized, and "the dream team" members think it is important for our world to know what could happen if another asteroid were to hit Earth again.
http://articles.latimes.com/2010/mar/04/science/la-sci-dinosaurs5-2010mar05
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