Earth hasn't always had a 24-hour day. Here's what that means for the June solstice.
As the summer solstice draws closer, Stephen Meyers has been welcoming the few extra minutes of sunlight each day that light up his walk home. He knows that after the year’s longest stretch of sunlight on June 21, the days will get shorter as the seasons shift and winter approaches.
But Meyers, a geoscientist at the University of Wisconsin, Madison, knows something that gives him a longer view: Over billions of years of Earth’s history, the time it takes Earth to rotate once on its axis has been getting longer.
Meyers and a colleague recently showed that 1.4 billion years ago, a single “day” lasted only about 18 hours. And changes in the gravitational dance between our planet and the moon are causing Earth’s day to get ever so slightly longer each year.
“So if I just wait a few hundred million years,” he says, “I’ll get that extra hour back!”
So, what’s been altering Earth’s days over geologic time, and does this mean anything for solstices past and future? Here’s the breakdown.