talking about -- imagine an elephant, the watt of an elephant concentrated on an area the size of a postage stamp. that's the kind of crushing force you've got to deal with. also it's dark. when you get down below 1,000 feet down, sunlight never penetrates and you're in this world of total permanent darkness. it's alien world down there. it's quiet, cold, and dark. >> and then the seabed, it's just under three miles down. that's abiliout 15,000 feet. they're talking about concerns or the impact of silt on finding the black box and on the search. what's the impact of that? many of us have no idea what they're talking about when they talk about silt on the seabed. >> over the centuries if deby that filters down from the surface world, things die and disintegrate and filter down and become clay like muck. and things fall into there and they can disappear. we don't really know, it hasn't listen characterized what's down there, is it mountainous, rugged, flat?