The oldest sea is the Pacific Ocean.
While the term "sea" is often used for smaller bodies of water connected to an ocean, in the context of major oceanic divisions, the Pacific Ocean is the oldest ocean basin. Its oldest rocks, found at the bottom of the Pacific, have been dated to approximately 200 million years old. This means that parts of the Pacific Ocean floor have been around much longer than other ocean basins like the Atlantic or Indian Ocean.
The age of the Pacific Ocean is due to the ongoing processes of plate tectonics, where new oceanic crust is formed at mid-ocean ridges and older crust is subducted (pushed down) beneath continents or other oceanic plates. The Pacific Ocean has experienced significant subduction throughout its history, which has consumed much of its older crust.
Therefore, when asked which sea is the oldest, in the context of the larger oceanic bodies, it is the Pacific Ocean that holds the title.
