Since 1980, The Notion that Mass Extinctions at the End of the Cretaceous Period

Reading Passage Question 

Since 1980, the notion that mass extinctions at the end of the Cretaceous period 65 million years ago resulted from a sudden event has slowly gathered support,although even today there is no scientific consensus. In the Alvarez scenario, an asteroid struck the earth, creating a gigantic crater. Beyond the immediate effects of fire, flood, and storm, dust darkened the atmosphere, cutting off plant life. Many animal species disappeared as the food chain was snapped at its base. Alvarez’s main evidence is an abundance of iridium in the KT boundary, a thin stratum dividing Cretaceous rocks from rocks of the Tertiary period. Iridium normally accompanies the slow fall of interplanetary debris, but in KT boundary strata, iridium is 10–100 times more abundant, suggesting a rapid, massive deposition. Coincident with the boundary, whole species of small organisms vanish from the fossil record. Boundary samples also yield osmium isotopes, basaltic sphericals, and deformed quartz grains, all of which could have resulted from high-velocity impact.

Palaeontologists initially dismissed the theory, arguing that existing dinosaur records showed a decline lasting millions of years. But recent studies in North America, aimed at a comprehensive collection of fossil remnants rather than rare or well-preserved specimens, indicate large dinosaur populations existing immediately prior to the KT boundary. Since these discoveries, doubts about theories of mass extinction have lessened significantly. Given the lack of a known impact crater of the necessary age and size to fit the Alvarez scenario, some scientists have proposed alternatives. Courtillot, citing huge volcanic flows in India coincident with the KT boundary, speculates that eruptions lasting many thousands of years produced enough atmospheric debris to cause global devastation. His analyses also conclude that iridium in the KT boundary was deposited over a period of 10,000–100,000 years. Alvarez and Asaro reply that the shock of an asteroidal impact could conceivably have triggered extensive volcanic activity. Meanwhile, exploration at a large geologic formation in Yucatan, found in 1978 but unstudied until 1990, has shown a composition consistent with extraterrestrial impact. But evidence that the formation is indeed the hypothesized impact site remains inconclusive.

“Since 1980, the notion that mass extinctions at the end of the Cretaceous period”- is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 2 comprehension questions. The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation 

1. It can be inferred from the passage that supporters of the Alvarez and Courtillot theories would hold which of the following views in common?

1. The KT boundary was formed over many thousands of years.
2. Large animals such as the dinosaurs died out gradually over millions of years.
3. Mass extinction occurred as an indirect result of debris saturating the atmosphere.
4. It is unlikely that the specific cause of the Cretaceous extinctions will ever be determined.
5. Volcanic activity may have been triggered by shock waves from the impact of an asteroid.

2. It can be inferred from the passage that supporters of the Alvarez and Courtillot theories would hold which of the following views in common?

1. The KT boundary was formed over many thousands of years.
2. Large animals such as the dinosaurs died out gradually over millions of years.
3. Mass extinction occurred as an indirect result of debris saturating the atmosphere.
4. It is unlikely that the specific cause of the Cretaceous extinctions will ever be determined.
5. Volcanic activity may have been triggered by shock waves from the impact of an asteroid.

Suggested GMAT Reading Comprehension Questions

• A One-Child Policy was Implemented in China in 1979
• Seeking a Competitive Advantage, Some Professional Service Firms
• On the surface, the Conquest of the Aztec Empire by Herman Cortes
• But Man is Not Destined to Vanish. He can be Killed, but he cannot be Destroyed, Because his Soul is Deathless and his Spirit is Irrepressible.
• When Literary Periods are Defined on the Basis of Men’s Writing, Women’s Writing Must be Forcibly Assimilated
• Behind Every Book Review There are Two Key Figures: A Book Review Editor and A Reviewer.
• Barbara Strozzi was a Singer and Composer of Madrigals, Aria
• During the Victorian Period, Women Writers were Measured Against A Social
• It Is Perhaps Not Surprising that Debate has Arisen Over Bioluminescence-Based Biotechnologies
• The Fact that Superior Service can Generate a Competitive Advantage
• The Origin of the Attempt to Distinguish Early from Modern Music
• The Phenomenon of College Basketball's Surging Popularity Remains a Challenge to Classify
• The United States Government has a Long-Standing Policy of Using Federal Funds to Keep Small Business Viable.
• A Recent Study has Provided Clues to Predator-Prey Dynamics in the Late Pleistocene Era.
• Even More Than Mountainside Slides of Mud or Snow, Naturally Occurring Forest Fires Promote the Survival of Aspen Trees.
• The Black Death, a Severe Epidemic that Ravaged Fourteenth Century Europe
• The System of Patent-Granting, Which Confers Temporary Monopolies for the Exploitation of New Technologies
• Ethnohistoric Documents from Sixteenth-Century Mexico Suggesting that Weaving and Cooking were the Most Common Productive Activities for Aztec Women
• Solar Ponds are Bodies of Water in Which Circulation is Incomplete and There is a Very High Salt Concentration that Increases with Depth
• Traditional Social Science Models of Class Groups in the United States are Based on Economic Status