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

2) The Renaissance period, which began in Italy in the 14th century, marked a renewed interest in art, literature, science, and philosophy.

3) The first successful mass-produced personal computer, the IBM PC, was introduced in 1981 and played a significant role in popularizing the use of computers in homes and offices.

4) The sitcom "Friends" is known for its iconic Central Perk coffee shop, where the main characters often gather.