90187 E Exemplar report. “What killed the dinosaurs.” What killed the dinosaurs – a good question? For about two hundred million years dinosaurs had ruled the world and occupied most niches. Dinosaurs had grown huge in every environment. Then about 65 million years ago they suddenly disappeared from the fossil record. What killed them will be discussed in this report. The meteorite/comet impact. In 1965 an American scientist named Luis Alveriz noticed a rock layer from around the world that had a peak of the mineral iridium within it. Iridium is an extremely rare mineral on earth and occurs in about 1 part per 10billion. In this layer the iridium levels peaked at 150 parts per million. Alveriz set out to find out what could have caused this layer. He noticed the layer (clay rich) occurred worldwide. He studied the layer in America, Italy, Spain and New Zealand. Alveriz worked out an event happened that caused iridium levels to be high, produced a clay layer that covered the world and indirectly wiped out the dinosaurs. Alverez realised that the only rocks on earth high in iridium were meteorites. He proposed that a meteorite about 10 km in diameter collided with the earth and created an enormous explosion that vaporised the meteorite and crustal rocks produced a layer of dust that stayed in the atmosphere for years depositing a clay layer worldwide. Alveriz realised that a large crater would have been formed about 100km in diameter but was unknown. After the release of his research geologists realised a large crater did exist in the Yucatan peninsula; the Chicxulub crater. It also had an age of 65 million years old. Shocked quartz was also found close to Chicxulub and further gave evidence of a meteorite impact event. Recent research has shown that chromium isotopes are not in the ratio expected of earth rocks. This suggests an extraterrestrial origin of the chromium. The isotope ratios are similar to that of meteorites. They indicate that the colliding body was a carbonaceous chondrite type meteorite. The shock wave from the impact would have started fires worldwide and evidence of these has been found in the clay layer. Charcoal has been found and in a few places in the world land was above sea level and evidence of forest destruction has been found. Inland from Greymouth is the only evidence from the Southern Hemisphere of a forest that was burnt out due to the shock wave. The eruption of the Deccan Traps. Geologists have known for many years that there were huge deposits of basalt in India. These basalts were flood basalts and were produced from huge eruptions of basalt as India crossed a hot spot in the Indian Ocean. There is no eruptive area today that would produce such massive out pouring of lava. Along with the lava was sulphuric acid and carbon dioxide. These were pumped into the atmosphere at alarming rates. The age of these basalts is also 65 million years. The key question is that did these eruptions elevate the levels of iridium in the clay layer. As yet geologists cannot answer this question. Research from the eruption of the Siberian traps 250 million years ago showed a major extinction event but no increase in iridium levels. Climate change. Recent research suggests that climate change may have been a big factor in the demise of the dinosaurs. Being big animals dinosaurs needed a lot of food. Any event that changed the climate would have changed the dinosaurs’ food supply. The evidence from Greymouth showed that the forest was replaced with ferns, a cool climate species and the forests did not return for about 1000 years. This evidence suggests that the climate of the world cooled very quickly 65 million years ago and food supplies were greatly reduced. What factors could have caused this cooling? Dust and sulfar in the atmosphere would have reflected light and cooled the surface of the earth. As the dust settled out forming the clay layer, the temperature would slowly have warmed up. Evidence suggests this would have been a slow event. Dinosaurs removed from their normal food would have died out. Mammals survived because they were better scavengers and smaller in size. The Tuautra also supports this idea. Being a small cold climate dinosaur it survived the event and still exists today. The cause. The dinosaurs died out because of two events working together producing a rapid climate change. The collision with the meteorite stressed an already fragile environment and supplying the high levels of iridium and the unusual chromium ratios. These could not have been formed on earth from earth rocks. The gases from the eruption of the Deccan traps had the earth cooling and the dust supplied by the collision tipped the climate into a strong cooling phase that took over 1000 years to recover. This lead to a lack of food for the big dinosaurs meant they died out. Both the meteorite collision and the Deccan trap eruption contributed to the end of the dinosaurs. It is not quite true to say the dinosaurs died out as we now know birds have evolved from the dinosaurs and are still around today. The reason they survived is that they were warm blooded and small and were able to move around easily. References used: “Fatal Impact” C J Hollis RSNZ Alpha 116 2003. Global Warming, not death of the dinosaurs, led to the rise of mammals Roger Highfield www.telegraph.co.uk/news/uknews/1546965 A fiery death for Dinosaurs? Amit Asaravala www.wired.com/print/science/discoveries/news/2004/05/63613