Paleontology Mock Tests

The following passage is an excerpt from an article about paleontology. The extinction of the non-avian dinosaurs, along with many other species, approximately 66 million years ago is one of the five major mass extinctions in Earth's history. This event, known as the Cretaceous-Paleogene (K-Pg) extinction, eliminated approximately 75 percent of all species on Earth, including all non-avian dinosaurs, pterosaurs, marine reptiles, and many species of plants and insects. For decades, the cause of this mass extinction was debated. Some scientists proposed that gradual climate change, volcanic activity (such as the Deccan Traps eruptions in modern-day India), or sea level changes were responsible. However, the leading hypothesis, first proposed by Luis and Walter Alvarez in 1980, is that a massive asteroid impact caused the extinction. The evidence for this hypothesis centers on a thin layer of sediment found worldwide that dates to exactly 66 million years ago and contains an unusually high concentration of iridium—a rare element on Earth's surface but common in asteroids and meteorites. Below this iridium layer, dinosaur fossils are abundant; above it, they are entirely absent. In 1991, scientists identified a massive crater in the Yucatán Peninsula of Mexico, called the Chicxulub crater, which dates to precisely 66 million years ago and is the right size (approximately 180 kilometers or 110 miles in diameter) to have been created by an asteroid estimated to be about 10 kilometers (6 miles) wide. The impact would have released energy equivalent to billions of nuclear bombs, triggering massive tsunamis, wildfires, and earthquakes. Most critically, the collision would have ejected enormous quantities of dust and sulfur aerosols into the atmosphere, blocking sunlight for months or years. This "impact winter" would have halted photosynthesis, collapsing food chains from the bottom up: plants and phytoplankton would have died first, followed by the herbivores that ate them, and then the carnivores that preyed upon them. Small animals, particularly those that could burrow, eat seeds, or survive in aquatic environments, were more likely to survive the catastrophe. Birds, which are the only surviving lineage of dinosaurs, survived likely because they were small, could fly to escape immediate effects, and could subsist on seeds and detritus. According to the passage, what is the key evidence supporting the asteroid impact hypothesis for the K-Pg extinction?

The following passage is an excerpt from an article about paleontology. The extinction of the non-avian dinosaurs, along with many other species, approximately 66 million years ago is one of the five major mass extinctions in Earth's history. This event, known as the Cretaceous-Paleogene (K-Pg) extinction, eliminated approximately 75 percent of all species on Earth, including all non-avian dinosaurs, pterosaurs, marine reptiles, and many species of plants and insects. For decades, the cause of this mass extinction was debated. Some scientists proposed that gradual climate change, volcanic activity (such as the Deccan Traps eruptions in modern-day India), or sea level changes were responsible. However, the leading hypothesis, first proposed by Luis and Walter Alvarez in 1980, is that a massive asteroid impact caused the extinction. The evidence for this hypothesis centers on a thin layer of sediment found worldwide that dates to exactly 66 million years ago and contains an unusually high concentration of iridium—a rare element on Earth's surface but common in asteroids and meteorites. Below this iridium layer, dinosaur fossils are abundant; above it, they are entirely absent. In 1991, scientists identified a massive crater in the Yucatán Peninsula of Mexico, called the Chicxulub crater, which dates to precisely 66 million years ago and is the right size (approximately 180 kilometers or 110 miles in diameter) to have been created by an asteroid estimated to be about 10 kilometers (6 miles) wide. The impact would have released energy equivalent to billions of nuclear bombs, triggering massive tsunamis, wildfires, and earthquakes. Most critically, the collision would have ejected enormous quantities of dust and sulfur aerosols into the atmosphere, blocking sunlight for months or years. This "impact winter" would have halted photosynthesis, collapsing food chains from the bottom up: plants and phytoplankton would have died first, followed by the herbivores that ate them, and then the carnivores that preyed upon them. Small animals, particularly those that could burrow, eat seeds, or survive in aquatic environments, were more likely to survive the catastrophe. Birds, which are the only surviving lineage of dinosaurs, survived likely because they were small, could fly to escape immediate effects, and could subsist on seeds and detritus. According to the passage, what is the key evidence supporting the asteroid impact hypothesis for the K-Pg extinction?