Final answer:
The correct statements describing the oceanic crust are B and E, indicating that it is formed at zones of volcanic activity on the ocean floor and contains silicate minerals high in iron and magnesium. The oceanic crust is composed of mafic rocks like basalt and is constantly renewed, making it much younger than 4 billion years.
Step-by-step explanation:
The student's question, 'Which statements describe oceanic crust?' can be answered by selecting two correct statements from the provided options. The oceanic crust is a significant aspect of Earth's geological makeup, covering 55% of Earth's surface and being mostly submerged under the oceans.
The correct answers to the question are:
B. It is formed at zones of volcanic activity on the ocean floor.
E. It contains silicate minerals high in iron and magnesium.
The oceanic crust is estimated to be about 6 kilometers thick, which contradicts statement D, and it principally consists of volcanic rocks like basalt and gabbro, which are mafic. These mafic rocks are rich in elements such as silicon, oxygen, iron, aluminum, and magnesium. Oceanic crust is composed mainly of these igneous rocks formed from cooling lavas, and not all types of rocks, which discounts statement C. Furthermore, the assertion that the oceanic crust's age can be over 4 billion years old is incorrect (A) because it is constantly being renewed at a fast geological rate due to the process of seafloor spreading. The renewal rate suggests that the oceanic crust's age falls under 200 million years, much younger than the 4 billion years indicated in statement A.