'Slushy' Earth: The slightly warmer cousin of the infamous Snowball Earth

About 650 million years ago, during the last global ice age, Earth was a giant frozen snowball. As the ocean chemistry started to change and the ice began to melt, Earth’s surface transformed into what scientists are calling a “slushy” planet.

Understanding the last global ice age

During a period of time ranging from 635 million to 650 million years ago, Earth went through an intense global ice age known as “Snowball Earth.”

During this time, glaciers covered almost the entire planet, from the poles all the way to the equator. The oceans were capped with thick layers of ice, and the continents were buried under massive ice sheets.

It was so extreme that if you were looking at Earth from space, it would have looked like a giant snowball, hence the nickname.

Life back then was pretty simple, mostly microscopic organisms living in the oceans. These tiny life forms had to survive under the ice, where some sunlight could still filter through.

Volcanic activity continued beneath the icy surface, releasing carbon dioxide into the atmosphere. Over tens of millions of years, this buildup of greenhouse gases eventually warmed the planet enough to start melting the ice.

That’s how Earth reached the “slushy” planet phase, which is the topic of this research.

Slushy Earth and “plumeworld ocean”

Thankfully, Earth, much like its current inhabitants, has a knack for adaptation and survival.

A recently concluded study led by Virginia Tech has given us an icy peek into the past, one that unveils a fascinating era known as the “plumeworld ocean” epoch.

This time slot on our planet’s timeline marked a significant moment. Imagine high levels of carbon dioxide acting like an invisible blowtorch, coaxing the frozen Earth into a vast, rapid meltdown.

“Our results have important implications for understanding how Earth’s climate and ocean chemistry changed after the extreme conditions of the last global ice age,” said lead author Tian Gan, a former Virginia Tech postdoctoral researcher. 

Earth before turning slushy

Let’s shift our attention back to the Snowball Earth period of around 635 to 650 million years ago. As mentioned, this was the time when our Earth was deep-frozen, and polar ice caps started encircling the planet like an icy belt.

This expansion of ice had a reflective effect, bouncing sunlight away from Earth and sending our temperatures on a downward spiral.

“A quarter of the ocean was frozen due to extremely low carbon-dioxide levels,” said co-author Shuhai Xiao, who recently was inducted into the National Academy of Sciences.

Effect of inactivity

Imagine someone pressing the pause button on the planet. That’s pretty much what happened.

The surface ocean sealed up, and a chain reaction of inactivity followed. First, the water cycle locked up — no evaporation, not much precipitation.

Without water, a fundamental carbon-dioxide consuming process known as chemical weathering, which essentially involves rocks eroding and disintegrating, slowed down dramatically.

The result? Carbon dioxide began to pile up in the atmosphere, turning into a thermal blanket of sorts.

Like a tightly wound spring, pressure built until the high levels of carbon dioxide were enough to shatter this ice age. When that happened, it wasn’t just a slow thaw — it was a climatic catastrophe.

“Plumeworld ocean” epoch

The Earth took a sudden U-turn and became “slushy”.

As the heat built up, the ice caps began retreating, and our climate started shifting back towards the warmer side.

And when we say warmer, we’re talking about a scorching swing from minus 50 to 120 degrees Fahrenheit (that’s minus 45 to 48 degrees Celsius).

The ice didn’t gently melt into the sea. Instead, think of it as reverse tsunamis of glacial water charging from land into the sea, creating vast pools over the extra salty, extra dense ocean water.

How do we know this is true?

How did the researchers uncover this prehistoric tale of the slushy Earth? The answer lies in a set of carbonate rocks that formed as the global ice age was wrapping up.

Upon analyzing the relative abundance of lithium isotopes within these rocks, a geochemical signature was found that supported the “plumeworld ocean” theory.

The data showed that the signatures of freshwater were stronger in rocks formed under nearshore meltwater than those formed offshore, deep under the salty sea.

This finding falls perfectly in line with what our researchers had theorized.

Slushy Earth’s resilience

To sum it all up, these findings bring the limits of environmental change into sharper focus, as Xiao mentions.

They also shed light on the frontiers of biology and the incredible resilience of life under extreme conditions — be it hot, cold, or slushy.

In the end, probing into Earth’s slushy past isn’t a mere indulgence in nostalgia. It’s a way to understand our present and prepare for our future.

In understanding how our planet has weathered past climatic earthquakes, we can better equip ourselves to navigate the potentially stormy climate shifts in our future.

Can the lessons from our past guide us towards a more resilient future? Let’s hope so.

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Collaborators include Ben Gill, a Virginia Tech associate professor of sedimentary geochemistry; Morrison Nolan, a former graduate student now at Denison University; and other significant contributors.

The study is published in the journal Proceedings of the National Academy of Sciences.

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