Page 215 - NS-2 Textbook

210 NAUTICAL SCIENCES

Mineral crystals often solidify or encrust around tiny Research has been under way for years to try to de-
objects on the sea bottom, forming Ilodllies, or lumps of velop an economical means of retrieving this wealth
metal. The most valuable of these are manganese nod- from the deep ocean bed, but because of the great depths
ules, which are also rich in copper, nickel, and cobalt. involved (12,000 or more feet), it is a difficult task. Those
These lumps of almost pure metals have grown over mil- who figure out how to do it will be able to gain untold
lions of years and literally pave the ocean bottom over wealth and much-needed resources for the world.
wide areas. Some of these manganese nodule beds Corillg tlte Seabed. Most deep seabed samples are
stretch for thousands of miles across the mid-latitude taken by coring. Corillg is done by dropping a weighted
oceans. They are especially abundant in very deep water tube vertically into the seabed so a cylinder of sediment
in a broad band from California to Midway Island, in a is trapped inside. It can then be pulled to the surface.
triangular area southeast of Japan, in the Baltic Sea, off Studying the cores and the shells of tiny animals in
the U.S. East Coast, and in a band from Brazil to South the ooze and sediments tells a great deal of the history of
Africa. that part of the ocean. Fossils give clues about the geo-
logical age of the strata of sediments in which they are
found. Animal and plant fossils indicate the tempera-
tures of the sea when these living things existed.
The standard piston coring tube cannot penetrate be-
yond 100 feet into the sediments, and 50--60 feet is the
norm. To get greater core lengths, hollow rotary drills are
now being used in advanced oceanographic research.
The rotary drills can drill in deep water and obtaln cores
thousands of feet long (in segments).
Deep-water drilling has told us much about the his-
tory and composition of the oceans and their sea floors,
as well as about the continents of Earth. Such drilling
showed that the North Atlantic began to form about 200
Piston withdrawn million years ago and the South Atlantic about 150 mil-
lion years ago. Mineral and oil deposits beneath the
ocean floor have also been located by deep-water
CONlhavledto drilling. Deep-ocean cores have confirmed the theOlY
slIrlllceWlthsample
that Earth's surface is made up of moving plates. II

tube CRITICAL THINKING
1. It has often been said that more is known about the
topography of the surface of the Moon than about the
core of characteristics of the sea floors. Investigate the kinds
sediment
of equipment now being developed to better map and
for study
investigate the nature of the deep ocean floors and
their composition.

Study Guide Questions
J-..-"---------- cutting tip
1. How did Navy hydrophones open a whole new area
of study for oceanographers?
2. What are the two main levels in the relief of the
Earth?
3. What are other names for the deep ocean floor?
A schematic view of a piston corer. When the corer hits the bottom, 4. A. How does an echo sounder determine the depth
the piston stops. The momentum of the tube carries it into the sed- of ,vater?
iment. The piston creates a partial vacuum in the tube so that up to
60 feet of sediment core may be obtained. As the corer is raised to B. If it takes 5~ seconds for an echo to return to
the surface, the sediment sample is held in by clamps that close au- an echo sounder, how deep is the water in that
tomatically over the end of the tube. spot?