Besides food, what useful does the sea supply?

Besides food, what useful does the sea supply?
The seas are huge storehouses of valuable items. Apart from food, the waters and rocks supply many chemicals and minerals useful in medicine and industry. salt, magnesium, iodine and bromine are extracted from seawater. From shallow seas, dredging vessels haul up sand, gravel and tin and even diamonds. Oil and gas is piped up from the depths of the sea in many parts of the world.

Nowadays, special ships are being developed to suck up millions of metallic lumps from the ocean floor. These lumps, called manganese nodules will yield not only manganese but also cobalt, copper nickel and other useful substances. As the mines on land become exhausted, we will have to depend more and more on the mines of the sea.