1) The universe is estimated to be around 13.8 billion years old.

2) The invention of the printing press by Johannes Gutenberg in the 15th century revolutionized the spread of knowledge and played a key role in the Renaissance.

3) The word "oxygen" contains two vowels: O and E.

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