Do you wish you could have an extra hour in the day? Well, if you can wait a very long time, you’ll get it.

That’s because the length of the day is increasing, and has been for the last billion-plus years.

Scientists recently studied a large Cretaceous mollusk with unprecedented precision. Mollusk shells grow like tree rings, adding a little bit each day.

The researchers used lasers to drill tiny holes in the shell, each the size of a red blood cell—like microscopic core samples.

From these they could examine the shell’s growth not just by the day, but by the hour.

They found that 80 million years ago, when this animal was alive, each day was half an hour shorter than today.

Going back further, to 600-million-year-old tidal sediments in Australia, they determined the day was then 22 hours long.

And 1.4-billion-year-old rocks in China suggested a 19-hour day.

All this indicates that Earth was once spinning faster than today. What’s going on?

Well, you can blame it on the moon.

The moon’s gravity causes Earth’s tides, which pull on and bulge out the surface of the oceans. Like when a spinning skater decelerates by extending her arms, the expanding and contracting seas are slowly decelerating Earth’s rotation.

But don’t worry, it’s happening very slowly—just 1.8 milliseconds per century.

Meaning it will be 200 million years before you get that extra hour.