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Home page Solar and galactic influences Climate change Sea level change Continental drift Volcanic activity Asteroid impact Pathogens Other species
Interplanetary solid objects, such as meteors and asteroids, are common in our solar system and millions orbit the sun. These orbits frequently bring them into the gravitational pull of the Earth. Small bodies burn up in the upper atmosphere, sometimes causing a brilliant display in the night sky, but now and again a large one reaches the ground. Although all of these small descending objects are potentially dangerous their impact is usually not noticeable and causes no damage.  The most recent serious impact was in Tunguska, Siberia in 1908 when an object exploded 5-10 kilometres above the surface and flattened 800 sq miles of trees. The size of the body is estimated to have been only a few tens of meters in diameter. A large asteroid impact has been proposed as the cause of the extinction of the dinosaurs. The Cretaceous–Tertiary (K-T) extinction event, which occurred approximately 65.5 million years ago, was a large-scale mass extinction of animal and plant species in a geologically short period of time. Research has identified the Chicxulub Crater of 180 km diameter on the coast of Yucatan, Mexico, as the place where an impact of a body 10 km in diameter took place about the right time. Such an asteroid impact would have had catastrophic environmental consequences. It has been calculated that the dust cloud created would have blocked sunlight for perhaps a year. The asteroid landed in a bed of gypsum (calcium sulphate) which would have produced a vast sulphur dioxide aerosol. This would have further reduced the sunlight reaching the earth's surface by 10–20% and then precipitated as acid rain killing vegetation, plankton and organisms which build shells from calcium carbonate (coccolithophores and molluscs). It would have taken at least ten years for those aerosols to dissipate, which would have accounted for the extinction of plants and phytoplankton and of the organisms dependent on them (including predatory animals as well as herbivores). Global firestorms may have resulted from the heat pulse and the fall of incendiary fragments from the blast back to Earth. If widespread fires had occurred, they would have increased the CO2 content of the atmosphere and caused a temporary greenhouse effect once the dust cloud had settled and this would have exterminated the most vulnerable organisms that survived the period immediately after the impact. It would also have caused a huge tsunami in Cental America and the Atlantic Ocean reaching West Africa and even Europe.
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