Topic
Oceans
2 articles
Astronomy
Why are there two high tides a day and not one?
The Moon is only ever on one side of Earth, yet the sea climbs the beach twice a day. The second high tide arrives from the direction the Moon is not.
Chemistry
Why is the sea salty when the rivers filling it are not?
Almost every drop in the sea arrived down a river, and river water is not salty. Something happens where the two meet that never happens upstream.