Do the preparation task first. Then watch the video and do the exercise. Remember you can read the transcript at any time.
Bob Ballard, Oceanographer: We didn’t know why the ocean was salty, how it got its chemistry, until fairly recently. Children would ask you, 'Why’s the ocean salty?' We’d say, 'next question'.
We thought in the early days that it was the rivers, the obvious culprits bringing all this stuff in but the chemistry of the world’s oceans was not equal to the chemistry of the rivers coming in to it.
We didn’t know until 1979. We were driving along the East Pacific Rise and there was a black smoker in front of us. We call it a black smoker because it looks like black smoke but it’s not. It’s microcrystals of minerals so we discovered when we found the black smokers that the entire volume of the world’s oceans is going inside the Earth and out every 6 to 8 million years and it’s taking some of the chemicals it gets from rivers and it’s trading them for new chemicals and this is occurring all the way along the mid-ocean ridge that stretches around the planet like the seam in a baseball, and there are tens of thousands of magma chambers down there and the waters get into them and that’s how we get the chemistry of the world’s ocean and we didn’t know that!
© National Geographic
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