The Grand Canyon exposes rock layers spanning nearly 2 billion years of Earth's history. The oldest rocks, at the bottom, are metamorphic and igneous formations created when the continent was forming. The younger layers above contain fossils that document the evolution of marine life when the region was covered by ancient seas.
The passage suggests that
geological formations can serve as records of both Earth and biological history
the Grand Canyon was formed in a single geological event
the oldest rocks contain the most advanced fossils
the region has always been a desert environment
Correct Answer: A
Choice A is the best answer. The canyon reveals both rock formation and fossil evidence.
- Context clues: Rock layers show Earth's formation; fossils "document the evolution of marine life."
- Meaning: The formation serves as both geological and biological record.
- Verify: Nearly 2 billion years of Earth history plus evolutionary evidence.
💡 Strategy: When something provides multiple types of information, infer its value as a record.
Choice B is incorrect because layers span 2 billion years—not a single event. Choice C is incorrect because older rocks predate complex life; younger layers have fossils. Choice D is incorrect because the region was "covered by ancient seas."