...the rival theories. Reasons for the Cretaceous mass extinction have been hotly debated for more than 200 years, since the founding days of geology. Cretaceous mass extinction is referred to the mass extinction that happened in the period of Cretaceous (just after Jurassic), more than 100 million years ago. Many creatures, especially dinosaurs, disappeared in the end of Cretaceous. K-T layer which marks the boundary between the Cretaceous and the Tertiary becomes the key point for the solutions. Till now, four main theories which are gradualism, supernova, volcanism and cosmic impact, have been put forward to solve the scientific problem. And, the last three models belong to catastrophism in favor of sudden extinctions, opposite to gradualism. However, this essay will attempt to argue that cosmic impact should be the most reasonable explanation due to evidence that have been found up to now. In order to demonstrate it, this essay will analyze these different theories separately paragraph by paragraph, along with corresponding findings. In addition, it will compare rival theories. In the ‘gradualistic’ view (theory of gradualism), the Earth was a slowly evolving word and the turnover of living species had to be slow. According to Frankel C. (1999) an ammonite specialist reported in the mid1980s that the ammonite species declined progressively over more than 100 meters of strata- a drawn-out interval of one million year at least. Besides, the last one was found more than ten...
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...g Easier! Making Everythin ™ heory tring T S Learn: • The basic concepts of this controversial theory • How string theory builds on physics concepts • The different viewpoints in the field • String theory’s physical implications Andrew Zimmerman Jones Physics Guide, About.com with Daniel Robbins, PhD in Physics Get More and Do More at Dummies.com® Start with FREE Cheat Sheets Cheat Sheets include • Checklists • Charts • Common Instructions • And Other Good Stuff! To access the Cheat Sheet created specifically for this book, go to www.dummies.com/cheatsheet/stringtheory Get Smart at Dummies.com Dummies.com makes your life easier with 1,000s of answers on everything from removing wallpaper to using the latest version of Windows. Check out our • Videos • Illustrated Articles • Step-by-Step Instructions Plus, each month you can win valuable prizes by entering our Dummies.com sweepstakes. * Want a weekly dose of Dummies? Sign up for Newsletters on • Digital Photography • Microsoft Windows & Office • Personal Finance & Investing • Health & Wellness • Computing, iPods & Cell Phones • eBay • Internet • Food, Home & Garden Find out “HOW” at Dummies.com *Sweepstakes not currently available in all countries; visit Dummies.com for official rules. String Theory FOR DUMmIES ‰ by Andrew Zimmerman Jones with Daniel Robbins, PhD in Physics String Theory For Dummies® Published by Wiley Publishing, Inc. 111 River St. Hoboken, NJ 07030-5774 www...
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