Great Blue Hole

Looking into Earth’s Past

Orbit: Earth’s Extraordinary Journey

You only really understand just how important our orbit is for our planet when you look into the Earth’s past.

There is evidence in the most unexpected places. A few miles from here is one of the most spectacular wonders of the world, but I can’t see it from here because it’s underwater. I’m in Belize in central America and what I’m going to see is known as the Blue Hole. It’s not often that nature produces something as beautifully symmetrical as this. It’s almost a perfect circle. But it’s more than just a stunning piece of natural architecture. Because deep down there are clues to some of the most dramatic events in Earth’s history. The Great Blue Hole, sometimes known as a vertical cave or sinkhole, is located near Ambergris Caye, Belize.

Finally, I’ve reached my goal down here, at a depth of 40m, are stalactites. This is what I’ve come to see and they’re stalactites. But there is only one way I know of for stalactites to form. And it isn’t down here, in 40m of water, with sharks swimming nearby. Stalactites are created when mineral-rich water drips from the roof of a cave, over hundreds or even thousands of years, leaving behind mineral deposits. In other words, they didn’t form in the ocean. Stalactites like this can only ever form above ground.

And that means when these grew, the sea level was much, much lower than it is today. Scientists have precisely dated stalactites from the Blue Hole and, by comparing these and other sea level indicators from around the world, they’ve built up a picture of changing sea levels dating back hundreds of thousands of years. It reveals a striking pattern. Sea levels across the world have risen and fallen over time.

20,000 years ago, the entire surface of the world’s oceans was 120m below where it is today. So where did the ocean go? The answer is that it was on land but it wasn’t a liquid water, it was ice, because 20,000 years ago, our planet was in the middle of an ice age.

The Earth has experienced regular ice ages in a cycle going back several million years. These dramatic changes in the state of our planet are triggered by small changes in the Earth’s orbit.