Oldest ocean
Who
Pacific Ocean
Where
Pacific Ocean Pacific Ocean
When
The world's oceans are constantly changing in size as tectonics makes the great plates of the Earth's crust slowly move around. The Pacific is the oldest of the current ocean basins, with the oldest rocks on its floor being around 200 million years old. The Pacific is gradually shrinking in size by a few cm per year as the Atlantic Ocean expands due to plate tectonics.