Dinosaurs would still been alive - and humans may have never come into existence - had the asteroid that hit Earth and triggered the mass extinction 66 million years ago, struck some other part of the planet, a study claims. An asteroid, also known as the Chicxulub Impactor, hit Earth some 66 million years ago, causing a crater 180 kilometre wide. The impact of the asteroid heated organic matter in rocks and ejected it into the atmosphere, forming soot in the stratosphere. Soot is a strong, light-absorbing aerosol that caused global climate changes that triggered the mass extinction of dinosaurs, ammonites, and other animals, and led to the macroevolution of mammals and the appearance of humans. Researchers said that the probability of the mass- extinction occurring was only 13 per cent. This is because the catastrophic chain of events could only have occurred if the asteroid had hit the hydrocarbon- rich areas occupying about 13 per cent of Earth's surface. Researchers, led by Kunio Kaiho from Tohoku University in Japan, came by their hypothesis by calculating the amount of soot in the stratosphere and estimating climate changes caused by it using a global climate model. They thought that the amount of soot and temperature anomaly might have been affected by the amount of sedimentary organic-matter. Researchers analysed the amount of sedimentary organic- matter in Earth to obtain readings of temperature anomaly caused by soot in the stratosphere. The relationship between the findings and concluded that the significant cooling and mass-extinction event could have only have occurred if the asteroid had hit hydrocarbon-rich areas occupying about 13 per cent of Earth's surface. If the asteroid had hit a low-medium hydrocarbon area on Earth - occupying about 87 per cent of planet's surface - mass extinction could not have occurred and the Mesozoic biota could have persisted beyond the Cretaceous/Paleogene boundary. The site of the asteroid impact, therefore, changed the history of life on Earth. According to the study, soot from hydrocarbon-rich areas caused global cooling of 8-11 degree Celsius and cooling on land of 13-17 degree Celsius. It also caused a decrease in precipitation by about 70-85 per cent on land and a decrease of about 5-7 degree Celsius in seawater temperature at a 50-metre water depth, leading to mass extinction of life forms including dinosaurs and ammonites. At the time, these hydrocarbon-rich areas were marine coastal margins, where the productivity of marine algae was generally high and sedimentary rocks were thickly deposited. Therefore, these areas contained a high amount of organic matter, part of which became soot from the heat of the asteroid's impact. Researchers concluded that the Chicxulub impact occurred in a hydrocarbon-rich area and is a rare case of mass extinction being caused at such an impact site.
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