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Unformatted text preview: s very little of this element, but most asteroids contain a lot more. Debris thrown into the atmosphere by an asteroid collision would presumably contain large amounts of iridium, and atmospheric currents would carry this material all over the globe. A search of sedimentary deposits that span the boundary between the Cretaceous and Tertiary periods shows that there is a dramatic increase in the abundance of iridium briefly and precisely at this boundary. This iridium anomaly offers strong support for the Alvarez hypothesis even though no asteroid itself has ever been recovered.
9. According to paragraph 6, what made iridium a useful test of the Alvarez hypothesis?
○Its occurrence in a few locations on Earth against several locations on other planets
○Its occurrence in limited quantities on Earth against its abundance in asteroids
○Its ability to remain solid at extremely high temperatures
○Its ease of detection even in very small amounts 10. In stating that no asteroid itself has ever been recovered the author emphasizes which of the following?
○The importance of the indirect evidence for a large asteroid
○The fact that no evidence supports the asteroid impact hypothesis
○The reason many researchers reject the Alvarez hypothesis
○The responsibility of scientists for not making the effort to discover the asteroid itself
Paragraph 7: An asteroid of this size would be expected to leave an immense crater, even if the asteroid itself was disintegrated by the impact. The intense heat of the impact would produce heatshocked quartz in many types of rock. Also, large blocks thrown aside by the impact would form secondary craters surrounding the main crater. To date, several such secondary craters have been found along Mexico's Yucatan Peninsula, and heatshocked quartz has been found both in Mexico and in Haiti. A location called Chicxulub, along the Yucatan coast, has been suggested as the primary impact site. 11. The word intense in the passage is closest in meaning to
12. What is the purpose of paragraph 7 in the passage?
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○It proposes a decisive new test of the Alvarez hypothesis.
○It presents additional supporting evidence for the Alvarez hypothesis.
○It explains why evidence relating to the Alvarez hypothesis is hard to find.
○It shows how recent evidence has raised doubts about the Alvarez hypothesis
Paragraph 1: █ Cases in which many species become extinct within a geologically short interval of time are called mass extinctions. █ There was one such event at the end of the Cretaceous period (around 70 million years ago). █ There was another, even larger, mass extinction at the end of the Perm ian period (around 250 million years ago). █ The Permian event has attracted much less attention than other mass extinctions because mostly unfamiliar species perished at that time. 13. Look at the four squa...
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This note was uploaded on 09/17/2013 for the course LANGUAGE 13DL208 taught by Professor Wang during the Fall '13 term at East China Normal University.
- Fall '13