The ring of fire is where many volcanoes occur because the plate is subducted in nearly every region.

Pacific Plate

The Ring of Fire is largely a result of plate tectonics, where the massive Pacific Plate interacts with less-dense plates surrounding it.

The oldest oceanic crust is about 260 million years old it is due to the process of subduction ,oceanic crust tends to get colder and denser with age as it spread off the mid ocean ridges . It gets so dense that it sinks in the upper mantle (subduction).