ASBOG Fundamentals Of Geology (FG) Practice Exam

The age range of oceanic crust is governed by its cycle of formation at mid-ocean ridges and recycling at subduction zones. New oceanic crust is created at spreading centers, then moves away from the ridge as the plate cools and thickens. Because it’s dense, it eventually sinks back into the mantle at subduction zones, where it’s recycled. This continual turnover means oceanic crust doesn’t stay around for very long on geological timescales compared with continental crust. Because of this quick recycling, the oldest oceanic crust that’s still typical in the oceans is about 180 million years old. That age represents the upper limit you commonly see for everyday oceanic crust before it’s pushed back into the mantle. The other options would imply crust ages that are far older than what’s typically preserved in the ocean basins; in practice, crust older than roughly 200 million SAMPLEyears is rarely found in standard ocean basins because it has been subducted and recycled. So, the oldest typical oceanic crust is around 180 million years.