4. Read these sentences from the article. "Individual layers of ancient sediment form horizontal stripes on the rock. From a few
steps back, the rock wall looks like a cross-section of a giant, stone encyclopedia."
Why might the author have included this description of the rock wall?
A. to explain why the author quotes scientists in the article
B. to demonstrate why the author explains two different methods used to date the rise of
oxygen in the atmosphere
C. to show why the author presents information about different compounds in the article
D. to clarify why the author compares studying a rock formation to studying a book