3. The sidebar "How the Grand Canyon Formed" states that "the area was covered in sand dunes" 275 million years ago. What can you infer happened to the dunes? (A) They turned into rock. (B) They were washed away by rivers. (C) They became part of a mountain. (D) They were completely blown away by wind

The sand dunes that once dominated the area later underwent significant geological changes. Over millions of years, the immense pressure from sediments piling on top of them caused the dunes to compact and cement together, which transformed them into sedimentary rock, specifically sandstone. This process of lithification is quite fascinating as it showcases nature's incredible ability to recycle materials into new forms! As time marched on, various geological processes like erosion and uplift played a pivotal role in shaping the Grand Canyon's stunning vistas. Water from ancient rivers intertwined with tectonic shifts carved through these hardened dunes-turned-rock, creating the iconic gorges and cliffs we admire today. This evolution from sand to monumental canyon demonstrates the dramatic transformations Earth can undergo!