Ocean Blue

Why is it that we can’t go more than a few miles under water? I read somewhere it has to do with compression, but how exactly does this work? How is it that giant squids can survive deep under water but our submarines can’t? I mean, there must be literally hundreds of species of animals we have never seen before that thrive way down there! We can send people to the moon, but we can’t go more than a few miles under water at our own planet?

Not sure exactly what your question is.

The oceans are only a few miles deep. We’ve been to the bottom. We have special subs that can stand the pressure. We’ve seen lots of new species of animals on the ocean floors.

Were you under the impression that the coeans were tens or hundreds of miles deep?

The deepest point in the ocean is the Challenger Deep in the Pacific Ocean at 35,840 feet deep, which is about 6.78 miles. I don’t think a manned sub has been down that deep, but unmanned ROVs have.

Here’s a relevant Q&A from another site. According to the link, the deepest point is “Challenger Deep” in the Marianas Trench at 36,200 feet, or almost 7 miles down.

There’s still trenches which we have never explored, IIRC.
Squids and octopii can survive the pressures since they’ve evolved to be able to do so. They have no air sacks within their bodies which are susceptible to pressure changes, unlike humans who have two massive air containers in their chests.

The reason we cannot venture down to the very deepest depths (or find it very hard to) is because the pressure is so great that it’s extremely difficult to design an actual craft that is capable of moving around and being able to withstand the enormous pressures being exerted on it.

(sigh) Once again, in case you missed Q.E.D.'s post. :smack:

(I swear, that guy is always 1 minute ahead of me)


Water doesn’t compress (much) under pressure. Air compresses a lot. So critters that have air in 'em have trouble with getting crushed as the air in 'em compresses under pressure (every 33.3 feet of water adds an amount of pressure equal to that exerted on you by the column of air that normally stands on top of your head and reaches to the tippy top of the sky). The practical upshot of this is that a given VOLUME of air (1 litre) will compress to 1/2 of it’s volume every 33.3 feet down you go. So at 33.3 feet it becomes 1/2 litre, at 66.6 it halves again to 1/4 litre and so on. This presents 3 problems, possibly more if I get on a roll.

First, if you hold your breath and head on down (we’ll assume you can hold your breath a long time) the 1 litre of air in your lungs will be down to 1/8 by the time you reach 100 feet. 1/64 by the time you reach 200 feet (and you’re giddy with nitrogen narcosis by now, but that’s not part of the OP). So by now you’re pretty much empty (volume-wise) and the air in your airy bits are no longer helping you retain your more or less yubular shape. Your chest caves in. You are now crab food.

Second, if you are a diver, every breath you take is subject to the same law. So if you normally inhale 1 litre of air at sea level, you will inhale twice that amount (because it is compressed from the pressure of your current depth) at 33.3 feet. 4 times that amount at 66.6 feet, etc. So if you are planning a deep dive and have the equivalent of 100 litres of air in your tank, you can’t stay down too long cuz you’ll run out of air more quickly the deeper you go. Same kind of issue gets you when you start to surface: If you have a full 1 litre breath of air and start to ascend from 66 feet, you need to keep in mind that you really have 4 litres of air in your lungs. So as you ascend you need to exhale so you don’t pop like a balloon (which DOES pop when it gets way up high near where the airplanes and big birdies go). Actually you won’t really pop because I don’t think anyone has the intestinal fortitude to keep the air in as it expands.

Third problem is if you eat chili or some other gas-producing food the night before you dive. If your intestine creates a regular sized fart at 66 feet and you start to ascend, it will expand to 4 times the normal size by the time you reach the surface! I understand the results are … incredible.

There are other issues that come up when you get REALLY deep. Nitrogen concentrations get real high in your body causing narcosis (you feel a bit high and silly) as well as over saturating your tissues. As you decompress, the gas “undisolves” from your tissues and you fizz (bends). A Way around this is to substitute the nitrogen in your air supply with helium. I’m not sure who figured this out, but I’m sure the deep compression divers laugh their bits off talking like Donald Duck).

How sperm whales make it at depth I have no idea. Giant squids got no air in 'em so they don’t get crushed. Do the math: 2 miles under water (10,560 feet) puts 317 atmospheres of pressure on you. Remembering that a volume gets halved every 33.3 feet that means that a litr of air would get squished down to … what … a rock of air?