1) Michael Phelps, an American swimmer, has won a total of 28 Olympic medals, including 23 gold medals, making him the most decorated Olympian of all time.

2) The smallest unit of time is known as a zeptosecond, which is equal to one trillionth of one billionth of a second.

3) The word "mountain" contains three vowels: O, U, and A.

4) The Great Barrier Reef in Australia is the largest living structure on Earth and can be seen from space.