1. The periodic table was first proposed by Russian chemist Dmitri Mendeleev in 1869. 2. The temperature at which paper catches fire is 451 degrees Fahrenheit, the title of Ray Bradbury's famous novel "Fahrenheit 451". 3. The element oxygen makes up about 21% of the Earth's atmosphere. 4. The average human body is composed of roughly 60% water. 5. Water is the only substance that exists naturally as a solid, liquid, and gas.