You may have heard that time is a social construct, but that doesn’t stop it from having consequences in the real world. If you show up to a party 10 minutes before it’s scheduled to start, you’ll likely be the first one there, and if you arrive to an interview 10 minutes late, you likely won’t get the job. But how did humanity agree on when and how to observe certain times of day?

In their new video, the It’s Okay to Be Smart team explains how humans “invented” the modern concept of time. The increments we use to measure time, like seconds, minutes, and hours, come from the ancient civilizations of the Egyptians and the Babylonians. Early clocks, like sundials and water clocks, were pretty crude, so people couldn’t pinpoint a time like noon down to the second even if they wanted to. But as clocks became more accurate, the problem wasn’t being unable to tell time accurately, but deciding which clocks qualified as “accurate” in the first place.

In 1884, President Chester A. Arthur organized the International Meridian Conference with the intention of deciding on a uniform definition of time to be followed around the world. The attendees ended up choosing the meridian running through Greenwich, England as the official Prime Meridian, and all clocks would be measured against the clock in the town’s observatory. Greenwich Mean Time is still used as the standard world time today.

Check out the full story below.

[h/t It’s Okay to Be Smart]