1) The first consumer digital video recorder (DVR), the TiVo, was introduced in 1999 and allowed users to record and store television programs for later viewing.

2) The Mona Lisa, painted by Leonardo da Vinci, is one of the most famous and valuable artworks in the world.

3) The first modern Olympic marathon race was held at the 1896 Olympics in Athens and has since become one of the most iconic and challenging events in athletics.

4) The Earth's core is primarily composed of iron and nickel and is as hot as the surface of the sun.