Timed Scanning/Skimming Practice 1 - 4 Questions in 5 minutes.

DIRECTIONS:
THE QUESTIONS IN THIS PRACTICE SET ARE ALL FACTUAL; THEY CAN BE ANSWERED BY MERELY SCANNING THE PASSAGE BELOW LOOKING FOR CLUE-WORDS FROM THE QUESTIONS.
IF IT IS YOUR STRATEGY TO READ THE QUESTIONS BEFORE READING THE PASSAGE YOU CAN DO THAT IN THIS ACTIVITY. JUST SCROLL TO THE BOTTOM OF THIS PAGE AND CLICK START NOW.
IF IT IS YOUR STRATEGY TO READ OR PREVIEW THE PASSAGE BEFORE LOOKING AT THE QUESTIONS, YOU MAY DO SO NOW.

65 million years ago the Cretaceous period ended. Many believe it ended abruptly. Sources vary widely regarding the changes that occurred, but on average they state that between 50 and 75% of all plant and animal life perished at this time. Of the animals, only amphibians and mammals survived. Fossilized dinosaur remains were first discovered in the mid-1800s. Since then, the reason for their demise has intrigued both scientists and lay-people. The most reliable testable hypothesis concerning their extinction was proposed by Alvarez and Alvarez in 1980.

Walter Alvarez, a geologist, was collecting sedimentary samples near Gubbio, Italy, working as part of a team measuring iridium. Not commonly found in Earth's crust and mantle, iridium has been regularly detected in scientific samples from other parts of the solar system; in other words, the team was searching for cosmic dust. Alvarez discovered - again, sources vary - a layer between 1 and 2 centimeters thick at the point believed to mark the boundary between the Cretaceous and Tertiary periods. This layer had an iridium content 30 times higher than its surrounding layers.

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