Chapter 7 - Functions and Graphs - 7.2 Domain and Range - 7.2 Exercise Set - Page 459: 51

$$ \text{All numbers that are greater than or equal to zero.}$$

We know that the domain is all possible inputs into the function. Since it would not make sense to use the equation for pressure as a function of depth below the ocean surface for negative values (which are above the surface, we find that the domain is: $$ \text{All numbers that are greater than or equal to zero.}$$