In many ways, the oceans still remain a great mystery to us. We don’t even know how old the oceans are. It seems certain that in the first stages of the earth’s growth no oceans existed.
Today, man is exploring the bottoms of the oceans to learn more about them. Covering the floor of the ocean to a depth of 12,000 feet is a soft, oozy mud. It is made up of the limy skeletons of tiny sea animals. The floor of the deep, dark regions of the sea, where the water is more than four miles deep, is covered by a fine, rusty-colored ooze called “red clay.” It is made up of tiny parts of skeletons of animals, the coverings of tiny plants, and volcanic ash.
The way the depth of oceans is measured today is by sending down sound waves which are reflected back from the bottom. The depth is found by measuring the time it takes for the sound wave to make the round trip and dividing this time in half.
Based on these measurements, we have a pretty good idea of the average depth of various oceans, and also the deepest point in each one. The ocean which has the greatest average depth is the Pacific Ocean. This is 14,048 feet. Next in average depth is the Indian Ocean which has an average of 13,002. The Atlantic is third with an average depth of 12,880 feet. The Baltic Sea is at the other extreme, with an average depth of only 180 feet!
The single deepest spot so far known is in the Mariana Trench. It’s in the Pacific near Guam, with a depth of 35,400 feet. The next deepest spot is in the Atlantic off Puerto Rico where it measures 30,246 feet. Hudson bay, which is larger than many seas, has its deepest point at only 600 feet!