How can we be so sure that the Marianas Trench is the deepest place on Earth when much of the ocean hasn’t been explored yet?
In: Geology
The whole thing has been mapped by satellites that can measure ocean depth. Most of the ocean is yet to have somebody physically go there and look around to see what lives there and such, but the topology is not unknown.
The extent to which the oceans are unexplored is often misleadingly exaggerated. We know the topology of the oceans, they’ve just not been mapped at particularly high resolution, and of course most of it won’t have been physically visited. That doesn’t mean we have absolutely no idea what’s there though.
The study of geology and plate tectonics gives us a general understanding of why places are deeper than others. The pacific plate, a dense flat basalt, is colliding with and going underneath (subduction) the Eurasian plate, with is much more “buoyant.” Every subduction zone where these collisions occur results in deep trenches and high mountain ranges.
So because of that, we know the deepest spots are likely to be off the coast of Asia/Oceania, the west coast of North America, or the west coast of South America (I am probably missing a few but you get the point).
With that known, satellites and other vessels can do further mapping of the areas and don’t have to scour the entire ocean for the deepest part. We know the dense basalt will be flat, and subducts beneath the buoyant continental crust.
We have mapped everything, we just haven’t done it in detail…
So we have undertaken large scale mapping of the entire ocean using technology like sonar – this is like flying over a mountain range and doing an aerial survey. This lets us see a lot of the big details like finding where the biggest mountains are, spotting the big valleys, and noting things like ‘that bit is a forest’.
What we have not done is the detailed mapping – this would be like sending down a team of climbers to map out all the small hills, rivers and paths, and do things like surveying all the plants and animals that you can’t see clearly in the big scale surveys.
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