Question

The oceanic crust is made of mafic rock called ________ and is about ________ thick on average

A) basalt, 7 km
B) marine sedimentary rocks, 25 km
C) basalt, 70 km
D) granite, 35-40 km

Answer 1

The oceanic crust is made of a mafic rock called basalt and is about 7 km thick on average, covering 55% of Earth's surface mostly beneath the oceans.

Step-by-step explanation:

The oceanic crust is predominantly composed of a type of mafic rock known as basalt. It covers about 55% of the Earth's surface, lying mostly beneath the oceans, and is typically around 7 kilometers thick. The mafic composition of basalt includes elements such as silicon, oxygen, iron, aluminum, and magnesium, and this crust forms from the cooling of volcanic lava on the seafloor or deeper within the Earth's crust.

Answer 2

The oceanic crust is made of basalt and has an average thickness of about 7 km, making option A) basalt, 7 km the correct answer.

Step-by-step explanation:

The oceanic crust is made of mafic rock called basalt and is about 7 km thick on average. Therefore, the correct answer to the student's question is A) basalt, 7 km. Basalt is the result of the cooling of volcanic lava and predominantly consists of elements such as silicon, oxygen, iron, aluminum, and magnesium. It is considerably thinner than the continental crust, which is made up of rocks like granite and has an average thickness of 20 to 70 kilometers.