When The Earth Turns into a Big Snowball

The Earth once froze completely, and the story behind it is a story of ice and fire… and some ice cubes!

Two years ago, we finally accomplished one of our dreams as a family: we bought a house. In retrospect, we were a bit delusional about this, but we wanted a semi-fixer-upper that we could renovate to our liking. Yes, we were influenced by the DIY (do it yourself)movement, which failed to tell us how hard this would be with two little kiddos and two 9-to-5s.

Luckily, even if the house looked ugly, it was liveable.

It was the peak of the summer, and we had gotten used to having an ice maker integrated into our refrigerator as we did in our rental apartment. But surprise, our new refrigerator didn’t have such a feature, and buying a new one wasn’t in our budget.

However, we wanted to have ice ready to cool our drinks. It was a particularly hot summer, and I was recovering from postpartum. So, my husband bought some ice-cube makers, among them, one that makes perfectly spherical ice cubes about 2.5 inches in diameter. As a good paleontologist, I call them Snowball Earths.

This past weekend, we had friends over, who appreciated the opportunity to have their setzler water with ice. When I mentioned providing a special treat of Snowball Earthed drink, puzzled looks emerged.

Snowball Earth? Why?

Well, here’s why.

Imagine a world so cold that glaciers covered almost the entire planet, from the poles to the equator. I’m not talking about a distant icy moon in our solar system — it’s our own Earth… about 700 million years ago. Yes, our dear Earth was once a big ball of ice and no fire… at least not for a while. But no worries, fire is coming into the story.

Many pieces of evidence make scientists believe that the Earth went through two major freezing events during a period known as the Cryogenian. These episodes, called the Sturtian and Marinoan glaciations, are often referred to as “Snowball Earth” events. During these times, our planet might have resembled a giant, frozen snowball for millions of years.

The Snowball Earth hypothesis suggests that Earth was nearly or entirely covered in ice twice, likely lasting for tens of millions of years each time. These frozen periods severly impacted the planet’s climate, oceans, and even life itself. But what led scientists to this conclusion, and how do we know this really happened?

The idea of Snowball Earth has been floating around the scientific world for a few decades. It was first coined by geologist Joe Kirschvink in 1989. He proposed that evidence in the rocks pointed to a planet that was almost entirely frozen over.

At first, this idea sounded like science fiction. How could Earth—especially its equator—be covered in ice? However, over time, more evidence started to support the theory, and other scientists started thinking about it more seriously.

One key piece of evidence comes from glacial deposits found in regions that, back in the Cryogenian, were located near the equator. These deposits include glacial dropstones—rocks that were carried by icebergs and dropped into ocean sediments when the ice melted.

Geologists have found these dropstones in places like Namibia, where it’s hard to imagine glaciers once floated. But the evidence doesn’t stop there.

Recent research by Dr. Elias Rugen and his colleagues from University College London (UCL) has added even more weight to the Snowball Earth theory.

They studied more than 2,000 zircon grains* from rocks in the Port Askaig and Garbh Eileach formations in Scotland and Ireland. Zircon grains are like little time capsules that help scientists determine the age of rocks.

Rugen’s team found that these rocks were laid down between 720 and 662 million years ago, right in the middle of the Sturtian glaciation. As Dr. Rugen explained, “These layers record a tropical marine environment with flourishing cyanobacterial life that gradually became cooler, marking the end of a billion years or so of a temperate climate on Earth.”

This research not only confirms the timing of the Sturtian glaciation but also provides a clear geological record of Earth’s transition from a warm, tropical world to a frozen one.

So, how did Earth end up freezing over? Scientists believe the answer lies in a combination of factors.

One major culprit seems to be the breakup of a supercontinent called Rodinia. As Rodinia split apart, it increased rainfall and weathering of rocks.

When rocks weather, they pull carbon dioxide (CO2) out of the atmosphere, which can cool the planet by reducing the greenhouse effect. Over time, this decrease in CO2 may have triggered the cooling that led to the Sturtian glaciation.

I said we were going to talk about fire too, so here it comes.

Volcanic activity also played a role. Around 717 million years ago, massive volcanic eruptions in what is now Canada may have sent sulfur aerosols into the atmosphere. These aerosols may have reflected sunlight away from Earth, further cooling the planet.

According to UCL geochemist Dr. Graham Shields, “These sulfur gas particles reflect incoming solar radiation and have a strong cooling effect.” Thus, this cooling might have been the tipping point that triggered the first Snowball Earth.

Once the ice started to form, a feedback loop kicked in. Ice reflects sunlight more efficiently than open water, so as more ice grew, less sunlight was absorbed, and the planet got even colder. This positive feedback, known as the ice-albedo effect, likely locked Earth into a deep freeze.

I know what you may be thinking: What happened to life on Earth while this was taking place? Well, as always, life finds a way…

While Earth’s surface was frozen, life below the ice somehow managed to survive. Before Snowball Earth, simple life forms like bacteria and algae dominated the oceans.

However, during the freeze, it’s believed that some of these organisms found refuge in pockets of open water or beneath the ice in shallow seas. There’s also evidence that multicellular life, including early sponges, may have evolved during or shortly after the Snowball Earth events.

Later on, as the glaciers retreated and Earth warmed up, life didn’t just survive — it thrived!

Dr. Shields points out that “all complex, multicellular life, such as animals, arose out of this deep freeze, with the first evidence in the fossil record appearing shortly after the planet thawed.” Once the planet warmed, life exploded in diversity, eventually leading to the Cambrian explosion, a period when most major groups of animals first appeared.

Dr. Rugen and his team’s new research provides crucial data that supports the Snowball Earth hypothesis. Their work confirms that the Scottish and Irish rocks they studied are part of this dramatic chapter in Earth’s history.

As Rugen puts it, “Most areas of the world are missing this remarkable transition because the ancient glaciers scraped and eroded away the rocks underneath, but in Scotland, by some miracle, the transition can be seen.”

Snowball Earth was a period of extreme cold, but it also set the stage for the incredible diversity of life that followed. Thanks to ongoing research, we’re continuing to uncover more about this fascinating and frigid era in Earth’s history. So, remember to support science and scientific discovery, for it is the key to better understanding and adapting to a changing world.

On the other hand, remember to call these spherical ice cubes “Snowball Earths” from now on; I promise you’ll impress your friends if you tell them this story. A real conversation ice-breaker! (Pun intended)