At a far simpler level, we can map the contours of the ocean bottom using an easy formula. For our activity, we will assume that depth, temperature and density make the sound travel at 1524 m (5000 feet) per second. The formula is:

(We divide by two because the time recorded is the time it takes for the round trip journey to go down and come back up again.)

Problem:
Use this formula to determine the missing depths based on readings taken 10 miles apart, then plot them to represent an imaginary section of ocean floor.

Click here to view the data table.

Solution:
Before you plot, check the depths of the missing depths. At 3 seconds, the depth is 7500 feet; at 4 seconds, 10,000.

Now plot the points. To check your graph, click here.

What is a fathom?
It is a nautical measure. One fathom equals 1.83 meters, or 6 feet.. A point 2,743 meters (9,000 feet) below the surface could also be said to be at a depth of 1500 fathoms. In English, to fathom means to understand thoroughly, to get to the bottom of a matter. Oceanographers fathom the ocean's depths.

More on Mapping:
Scientists now use a combination of sophisticated equipment to map the ocean floor and obtain three-dimensional models of its mountains, valleys, plains, and other geological features. Much remains to be done; an estimated 95 percent of the ocean floor is yet unmapped.

This NOAA bathymetric map of the Northeast Pacific shows the relative heights of the Juan De Fuca Ridge, Blanco Fracture Zone, and Gorda Ridge.

If you would like to learn more about the advanced mapping techniques used by US National Oceanic and Atmospheric Administration scientists, click here to link with their Web page. http://www.pmel.noaa.gov/vents/geology/methods.html