The assumption is the surrounding sediment can suffice for a good enough approximation. http://www.nytimes.com/2011/09/13/science/13qna.html http://www.nytimes.

The assumption is the surrounding sediment can suffice for a good enough approximation. http://www.nytimes.com/2011/09/13/science/13qna.html http://www.nytimes.com/2011/09/13/science/13qna.html