1) The process of photosynthesis, performed by plants, algae, and some bacteria, is responsible for producing the oxygen we breathe.

2) International relations encompass the study of relationships between nations, including diplomacy, treaties, and foreign policy. It examines the interactions and dynamics among different countries in the global arena.

3) In Norse mythology, Ragnarok is a cataclysmic event that signifies the end of the world. It involves a series of apocalyptic battles and natural disasters, leading to the destruction of the gods and the world as it is known. From the ashes, a new world and a new generation of gods emerge.

4) The Triple Crown in horse racing consists of three prestigious races: the Kentucky Derby, the Preakness Stakes, and the Belmont Stakes.