1) The concept of 3D printing, also known as additive manufacturing, was first introduced in the 1980s and has since revolutionized prototyping and small-scale production.

2) The ancient city of Rome was founded in 753 BC and went on to become one of the most powerful and influential civilizations in history.

3) The concept of proportional representation, used in some electoral systems, aims to ensure that political parties' representation in government aligns more closely with the proportion of votes they receive from the electorate.

4) The Earth's core is hotter than the surface of the Sun.