How does the Moon cause ocean tides?
The Moon's gravity pulls unevenly across Earth, stretching the oceans into two bulges. Earth rotates through them, giving most coasts two high tides a day.
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Science
Oceanography
What is plate tectonics, and how was it discovered?
Plate tectonics says Earth's rigid outer shell is broken into moving plates. It was assembled in the 1950s and 1960s from seafloor mapping, magnetic stripes, drilling and earthquake data.
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Why is the sea salty when the rivers feeding it are not?
Rivers carry small amounts of dissolved salts that the ocean collects, while evaporation leaves the salt behind and rain keeps rivers diluted. Vents and volcanoes add more.
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