Complex sentence: Most of the world reserves of potassium (K) were deposited as sea water in ancient inland oceans evaporated, and the potassium salts crystallized into beds of potash ore.
Split into simpler sentences: Most of the world reserves of potassium (K) were deposited as sea water in ancient inland oceans. After the water evaporated, the potassium salts crystallized into beds of potash ore.