The speed of light in a vacuum is 186,282 miles per second (299,792 kilometers per second), and in theory nothing can travel faster than light. In miles per hour, light speed is, well, a lot: about 670,616,629 mph. If you could travel at the speed of light, you could go around the Earth 7.5 times in one second.
Marco Polo (1254-1324) was an Italian voyager and merchant who was one of the first Europeans to travel across Asia through China, visiting the Kublai Khan in Beijing. He left in 1271 (he was a teenager at the time) with his father (Nicolo Polo) and uncle (Maffeo Polo); they spent about 24 years traveling.
Tooth sensitivity is caused when the outside of teeth, or the hard enamel, wears down or gums recede and the tiny tubes in the tooth dentin become exposed. Each of those tiny tubes contains a lot of nerve endings, and when they’re left open, it can hurt when you put hot or cold things in your mouth.