Question: What's at the bottom of the ocean or how deep do you think it goes down?

Susan Cartwright answered on 19 Jun 2015:

The deepest parts of the ocean are the subduction zones where one tectonic plate dives underneath another, causing a deep V-shaped groove. The very deepest is the Mariana Trench, which has a maximum depth of 11 km; that’s considerably deeper than Mt Everest (just under 9 km) is high.

At the bottom of the ocean is obviously the seabed (or sea floor, or ocean floor). This differs from the rocks of the continents in being much younger and mostly volcanic, produced by seafloor spreading at mid-ocean ridges. Iceland is a bit of mid-ocean ridge that has become elevated above sea level for some reason, and the high volcanic activity of Iceland is typical of these regions.

Living creatures exist even in the deepest ocean. They have not been well studied because they have evolved to live at the very high pressures of the deep sea, and bringing them to the surface usually kills them. Nowadays they are studied using either manned or remote operated submarines, but most of them cannot get as deep as the deep trenches: the Russian Mir manned research submersibles “only” get to 6 km, and they’re better than most. (About 98% of the ocean floor is accessible to the Mirs – there are two of them – but not the subduction trenches.)