The oldest ecosystems on Earth

The oldest seafloor is actually in one of the smaller seas: the Mediterranean, a relic of the earlier Tethys Sea, and is about 280 million years old. Most seafloors are only ~100--200m years old if that, and some basins (e.g, the Atlantic) only began to form ~170--200 mya.

I'd agree that the ecological niche of deep-sea hydrothermal vents is quite possibly the oldest of any, and may have originated life on Earth, there are no particularly old extant deep-sea vents.

By contrast there are continental strata which are many billions of years old. Some extant landforms, such as the Appalachian Mountains, are older than terrestrial life.