Thanks to Linode Cloud Computing for  supporting this episode of SciShow.

You can go to linode.com/scishow to learn more and get a $100 60-day credit  on a new Linode account. [♪ INTRO] Most of us can probably agree  that the passage of time has gotten a little weird lately. While it’s been a few years since  the COVID-19 pandemic started, it sometimes feels like  it’s only been a few months… and then it feels like a  decade…at the exact same time.

While that’s really all in our heads, the  length of a day is constantly changing. And a couple months back, we  recorded the shortest day ever… at least since atomic clocks  started keeping track for us. But while some events on and in Earth  might be trying to shorten the day, others are trying to make it longer.

We typically think of a day as  being exactly 24 hours long. That’s how we defined hours. But in reality, it’s sometimes a teeny  bit shorter, or a teeny bit longer, depending on how fast the  Earth is actually spinning.

And on June 29th, 2022, the Earth  was spinning even faster than normal, so the day was a record-breaking  1.59 milliseconds shorter. But that record is only for Earth’s  recent history…ever since humanity started keeping track of time  with super accurate atomic clocks. If you go even further into the past,  Earth’s day was hours shorter than it is now.

How do we know this? Well, scientists can use mollusk fossils  to measure how long the days were millions of years ago. These mollusks added daily layers of  calcium carbonate to their shells, so in general, thinner layers means shorter days.

By combining those measurements with  how much the ratio of different elements varied in the environment, research suggests  that about 72 to 84 million years ago, the average day on Earth was a whole  half hour shorter than it is now. In other words, the Earth was spinning so  fast that there were 372 days in a year, not 365…or 366 in a leap year. And if you go back all the  way to 1.4 billion years ago, days were less than 19 hours long.

How is that possible? Well, it  all comes down to Earth’s moon, and the fact that the Earth spins  faster than the Moon orbits around us. Because of that difference in speeds,  the Moon’s gravity exerts a kind of braking effect, slowing the Earth’s spin  by a couple of milliseconds each century.

But the length of a day can change  over even smaller time frames… not just years, but individual days. Usually, it has to do with how  Earth’s mass is distributed. It’s the same physics behind an  ice skater changing their spin by pulling their arms in, or by squatting  and holding out one of their legs.

And Earth has lots of matter to move around. Air, water, even rock itself  moves daily thanks to tidal forces Earth shares with the Sun and Moon. And ice growing at the poles helps squish  the Earth so it’s a little less spherical.

According to one hypothesis,  this record-setting day may be partially due to climate change. Since the ice sheets and glaciers  at the poles have been melting without refreezing to what  they were in past winters, they’re squishing the Earth  less and less each year. And like an ice skater spinning  faster after pulling in their limbs, the Earth spins a tiny bit faster, too.

The days get a little bit shorter, in  contrast to the general pattern of days getting longer over millions or billions of years. It’s a different kind of  wibbly wobbly timey wimey. Now, you and I did not notice  that missing 1.59 milliseconds, but our technology did.

For example, GPS works by sending  signals from a series of satellites to a receiver like your smartphone. It uses the Earth’s rotation rate,  along with the time that passes between the signals it sends, to calculate your  location or how far you’ve traveled. If the Earth is spinning at  minutely different rates each day, that can significantly mess up  where the GPS tells you you are.

Which can spiral into some serious  consequences depending on the technology. For example, scientists can use GPS  to monitor where storms, floods, and even wildfires may head, giving  people time to evacuate if need be. Now, to compensate for these  ever changing day lengths, the scientific community usually adds a  leap second to the year every few years.

But if this shortest day on record is any  indication that Earth will experience even more days that are shorter than average,  we might need to remove a second. And that rate might depend on factors like  how fast the polar ice caps continue to melt. But the Earth can only do so much to keep its  days short in the short term, astronomically.

The Moon is still up there, slowing us down. And if the lengthening continues the way  it has over the last 1.4 billion years, an Earth day will be a whole 25 hours  long in only about 250 million years. Since we only have so much time in  the day, some of us can really benefit from the extra time we save using Linode.

Linode is a Linux based cloud service provider. They help you do things like backup  your website to protect against losing previous versions and spending hours or  days trying to recover or recreate them. When you build a website on  Linode and enable backups, you’ll get an automatic daily  backup, 2-7 day old backup, and 8-14 day old backup.

So you can go back in time in case you  made a change that doesn’t work out. And if you want to backup  your work at different times from those automatic options, you can do that too. Linode lets you manually backup your  work at a time that makes sense for you, or schedule your backups in advance  so you don’t forget in the moment.

That peace of mind is $2 per month. And Linode doesn’t try to  pull the wool over your eyes. They tell you in bold writing when you’re  about to upgrade your service for an extra $2.

For that transparency and functionality, you can click the link in the description  or head to linode.com/scishow. That link gives you a $100 60-day  credit on a new Linode account.   Thank you to Linode Cloud Computing for supporting this SciShow video and thank you for watching! [♪ OUTRO]