OCEANIC FEATURES
If you were a sailor, how would you find out if they were any dangers on
the sea floor? How would you learn how deep the water is, or how water
depth changes from place to place? Before the 20th century,
the most common way to find the depth of the ocean was to use a sounding
line. This was a rope with a lead weight attached to the end. The rope
was tied in a knot every fathom (6 feet). A sailor would swing
the line overhead and off the ship, and count the number of knots that
went by before the weight hit the sea floor. This gave a good estimate
of depth.
This depth information was very important. It allowed ships to
navigate safely through unknown waters without being wrecked. By
collecting many observations, early oceanographers learned that the sea
floor gradually became deeper offshore. This region was called the continental
shelf. However, the longest sounding lines were at most 1600 meters
(1000 feet) long. Scientists and sailors quickly discovered that many
parts of the ocean were deeper than this, but they could not tell what
was there. Most people assumed the deep ocean floor was a broad, flat
plain between the continents.
Early exploration of the ocean bottom.
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