Re: how can animals survive thousands of feet under the sea

G'day Brett

Interesting question. I guess you're talking about the immense pressures 
that animals living down deep must endure.

It's simple physics really. Only gases are compressable. That leaves 
solids and liquids as incompressable.

As a mammal, if you dived down really really far, your bones and soft 
tissues (organs, blood, bones, muscles etc) would be fine. You can't 
compress them at depth because they are solids or liquids. However, the 
air spaces in your lungs would be squashed flatter than a pancake.

Same goes for a big Navy submarine - there is lots of air inside the hull 
which gets compressed at depth, and allows the outside metal hull to cave 
in. This is why submarines have to be really strong to withstand 
the "caving in" force. We could fill them with liquid (which you can't 
compress), but it'd make life pretty hard for the crews!

Animals living at depth generally aren't air breathing mammals, so because 
they don't have air spaces inside them (ie. they're virtually all soft 
tissue), they're fine at depth. They simply can't be compressed by the 
pressure.

Hope this explains it.

cheers,

Alastair