Tides are the rising and falling of ocean's water.
Tides are caused from the gravitational attractions between the Earth, sun, and moon. When the Earth, moon, and sun are positioned in a straight line the gravitational pull on the Earth is greater. But when the moon and the sun are at right angles to the Earth their gravitational pull is decreased. The oceans are salty because it washes down from the rocks on land. The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air.