ACT Science Test - Practice Test 3 — Flashcards

Questions below are based on the following passage:

The Cretaceous-Tertiary extinction (K-T) happened between 65 and 66 million years ago and is commonly known for the extinction event that killed the dinosaurs. Around 75%  of life on Earth, including dinosaurs, many plants, fish, and some mammals, ceased to exist after the K-T event.

Two scientists present theories to explain the K-T extinction event:

Scientist 1
The K-T extinction was precipitated by the collision of a large asteroid with the earth. The initial impact of this asteroid caused large tsunamis and earthquakes, immediately killing anything within thousands of miles. It also led to rapid changes to Earth’s climate. The massive dust cloud created by the impact blocked the sun, causing global temperatures to plummet. Fiery chunks of rock, exploding from the impact site, ignited huge fires across the planet. These fires decreased oxygen levels and increased levels in the atmosphere, leading to a greenhouse effect and climate change. All of these combined factors led to the massive K-T extinction. The main evidence for this impact theory is the 110-mile wide Chicxulub crater near the eastern coast of Mexico.

Scientist 2
The massive K-T extinction was caused by huge volcanic activity on the Earth. These volcanos, especially those that formed the Deccan Plateau in western India, became active during the same time as the K-T extinction. The volcanos spewed around 1.5 million square kilometers (580,000 square miles) of lava over the period of thousands of years. At the same time, these volcanos pumped , ash, and poisonous chemicals into the atmosphere. Eventually, this process would lead to ocean acidification, killing plankton and small marine life essential for food chain stability. Reduced solar intensity from the greenhouse gases, coupled with loss of food killed off much of the plant and animal life over the period of thousands of years, causing the K-T extinction.