We live in a base-10 world. The decimal system governs everything from the binary functions of computers to the amount of change you get when you buy a Mashed Potato Slurpee. So why isn't the standard Earth day just 10 hours long? Credit the Egyptians for that one.

As human civilization moved from transient hunter-gatherer societies to agricultural communities, people realized the need to tally their objects and property. (If you go out to pasture with five goats in the morning, then come back with three in the eveningâ€”and can't tell the differenceâ€”you're doing it wrong). The concept of written language was just catching on at that point, so people learned to count the same way kids do todayâ€”using their 10 fingers.

Egyptian hieroglyphs from as early as 3000 BC show the use of a base-10 decimal system. So why did they set their clocks to base-12? Many believe that the base-12 system arose from a counting system the Egyptians inherited from the earlier Sumerian culture, counting not by the whole finger but by each individual knuckle. That is, if you open your left hand and use the tip of your thumb to touch each of the three knuckles in your four fingers, you'll total 12. To measure time using this method, the Egyptians divided the day into 12-hour halvesâ€”or, more accurately, a ten hour day, two hours of morning and evening twilight, and 12 hours of darkness.