reply2spg wrote:Source - McGraw-Hills (Conquering Gmat, Drill # 1, Q # 4)

Iridium, a hard, whitish metal similar to platinum, is extremely rare on Earth. extremely high concentrations of Iridium on Earth result from only 2 scenarios : massive volcanic eruptios that release Iridium from deep within the Earth and meteorites that shower down on Earth from space. when scientists found concentrations of Iridium 30 times higher than normal in rock stratum from 65 million years ago, they concluded that a massive meteor or commet hit the earth and caused the massive extinction of the dinosaurs.

Which of the following, if true, most strongly supports the scientists conclusion?

1. Volcanos massive enough to generate high concentrations of iridium are very rare

2. massive volcanic erruptios occured frequently 80 million years ago.

3. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs

4. The massive extinction that occured 70 million years ago killed not only the dinosaurs but also 70% of all life on the earth

5. A comet struck the earth some 20 million years ago, but no widespread extinction occured

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