1) The Arctic Ocean is the smallest and shallowest ocean, located at the North Pole. It is covered by sea ice for much of the year.

2) Serena Williams, an American tennis player, has won a total of 23 Grand Slam singles titles, making her one of the most successful players in the history of the sport.

3) The ozone layer, located in the Earth's stratosphere, protects us from harmful ultraviolet (UV) radiation.

4) The world's oldest known living tree is a bristlecone pine named "Methuselah" in California, estimated to be over 4,800 years old.