Which statement about the age of rock layers in the Grand Canyon is accurate?

The statement that some layers in the Grand Canyon are nearly two billion years old is accurate because the geological history of the Grand Canyon reveals a complex timeline of rock formation. The rock layers at the bottom of the canyon, such as those from the Vishnu Schist and other ancient formations, date back to about 1.7 billion to 2 billion years ago. These ancient rocks provide critical evidence of the Earth's early geological processes and have undergone significant metamorphosis over billions of years.

In contrast, other statements do not align with the geological evidence present in the Grand Canyon. For instance, while it's true that many rocks are younger than 500 million years, this statement doesn't acknowledge the existence of much older formations. Similarly, asserting that all rock layers are the same age or all being approximately one million years old contradicts the well-studied stratigraphy of the canyon, which clearly shows a succession of different age layers with substantial variations in their ages.