The maximum age of oceanic crust is approximately

• A. 180 million years
• B. 2 million years
• C. 1 billion years
• D. 400 million years

Answer: (A)

Oceanic crust is constantly formed at mid-ocean ridges and recycled back into the mantle at subduction zones, so it doesn’t stay around for very long. The age pattern of the seafloor shows it gets older with distance from the ridges, but the oldest oceanic rocks are only about 180 million years old. This upper limit is supported by radiometric ages of basalts and the global seafloor age distribution, along with magnetic stripe evidence that records seafloor spreading. When oceanic crust reaches a trench, it is subducted and melted, removing it from circulation. Therefore, the maximum approximate age of oceanic crust is around 180 million years.