How Volcanoes Froze the Earth (Twice)

Summary

The video explores 'Snowball Earth,' a period of intense glaciation between 716 and 635 million years ago when the planet was covered in ice from the poles to the equator. It explains how volcanic activity, the breakup of the supercontinent Rodinia, and a dimmer sun caused Earth's temperatures to plummet. Geological evidence like dropstones and carbonate rock disappearance supports this theory. Despite the extreme cold, life managed to survive, and eventually, CO2 from volcanoes warmed the Earth again, leading to the emergence of diverse life in the post-glaciation Ediacaran period.

Takeaways

• ❄️ Earth experienced two intense global glaciation events between 716 million and 635 million years ago, known as Snowball Earth.
• 🌍 The world was covered in ice, including the tropics, with temperatures at the poles reaching as low as -130°C.
• 🪨 Evidence of these freezes comes from dropstones and carbonate rocks, which show ice extended from poles to the equator.
• 🔄 The glaciations were likely caused by disruptions to Earth's carbon cycle due to the breakup of the supercontinent Rodinia and the dimmer sun.
• 🌋 Volcanic activity, particularly from the Franklin Large Igneous Province, released sulfur dioxide, further cooling the planet.
• 🌡️ A runaway icehouse effect occurred, where the growing ice reflected more light, causing further cooling and ice expansion.
• 🧊 Life, including early photosynthetic organisms, managed to survive during the ice ages, possibly in areas of thin ice or open water.
• 💨 The glaciation ended when volcanic activity continued to emit CO2, eventually building up enough greenhouse gases to melt the ice.
• 🧬 Animal life, including sponges, survived through the Snowball Earth, leading to a burst of biodiversity in the following Ediacaran period.
• 📅 These glaciations were pivotal events in Earth's history, reshaping its climate, geology, and the evolution of early life.

Q & A

What is Snowball Earth?

Snowball Earth refers to two periods during the Cryogenian, between 716 and 635 million years ago, when the planet was almost completely covered in ice, including the equator.

How did scientists first discover evidence of Snowball Earth?

Scientists found evidence in the form of dropstones, which are rocks carried by glaciers and dropped into ancient ocean sediments. These dropstones have been found on every continent.

Why was it surprising to find evidence of ice at the equator?

It was surprising because the equator is typically warm. Scientists initially thought Earth may have tilted on its side rather than accept that the equatorial oceans froze.

What geological evidence supports the Snowball Earth hypothesis?

In addition to dropstones, scientists found evidence in the form of carbonate rocks. During the periods of glaciation, carbonate rock formation ceased due to the lack of weathering under ice-covered continents.

How did early life survive during Snowball Earth?

Scientists propose several models, including 'Slushball Earth,' where some equatorial areas remained ice-free, or that the ice was thin enough to allow sunlight to penetrate, enabling photosynthetic life to survive.

What role did volcanoes play in the formation of Snowball Earth?

Volcanoes emitted CO2 into the atmosphere, but when the supercontinent Rodinia broke up, it exposed large amounts of basalt rock, which absorbed CO2 rapidly, disrupting Earth's carbon cycle and leading to global cooling.

How did sulfur dioxide contribute to cooling the Earth during this period?

A massive volcanic eruption in the Franklin Large Igneous Province released sulfur dioxide into the atmosphere, which reflected sunlight and cooled the Earth further, contributing to the glaciation.

What is the runaway icehouse effect?

The runaway icehouse effect is a feedback loop where growing ice reflects more sunlight, causing more cooling and ice formation, making the process of freezing the planet unstoppable once ice extended below 30 degrees latitude.

How did Earth eventually thaw after the glaciations?

Volcanoes continued to release CO2 into the atmosphere, but with most rocks covered in ice, CO2 built up over millions of years, eventually warming the planet and melting the ice.

What happened to life on Earth after the ice melted?

After the ice melted, the oceans warmed, and life flourished, particularly during the Ediacaran period, which followed the Cryogenian and saw the emergence of new forms of animal life.

Outlines

00:00

❄️ The Frozen World of Snowball Earth

Paragraph 1 introduces the concept of Snowball Earth, a period between 716 and 635 million years ago when the planet was almost entirely covered in ice. Temperatures plummeted, even at the equator, and glaciation spread across land and sea. Scientists found evidence of this intense glaciation in dropstones across the world, which were carried by glaciers and icebergs before dropping into ancient oceans. This widespread presence of ice, confirmed by reconstructing Earth's past geography, reveals two significant glaciation episodes.

05:00

🌍 Life Under Ice and the Slushball Earth Debate

Paragraph 2 discusses the scientific debate on how life could have survived during the intense glaciations. While some evidence points to a 'Slushball Earth' model with unfrozen regions, other theories suggest that life, including cyanobacteria, persisted under or on top of ice sheets. The ice-covered planet led to minimal weathering, and carbonates disappeared from ocean sediments. As the ice began to melt, carbonate deposits returned, indicating that Earth's surface was once extensively covered in ice.

10:02

🌋 The Carbon Cycle and Rodinia’s Impact

Paragraph 3 explains how the Earth's carbon cycle was disrupted by volcanic activity during the breakup of the supercontinent Rodinia. This breakup exposed large amounts of basalt, which absorbed CO2 rapidly, cooling the Earth. Combined with a dimmer sun and sulfur emissions from volcanic eruptions, this led to a feedback loop where growing ice reflected more sunlight, accelerating cooling. Eventually, CO2 levels rose again due to ongoing volcanic activity, leading to the eventual melting of the ice.

⛏️ Runaway Icehouse Effect and the Recovery

Paragraph 4 describes the runaway icehouse effect, where growing ice reflected more sunlight, cooling the Earth further and leading to unstoppable glaciation. However, volcanic activity continued, and over millions of years, CO2 built up in the atmosphere, melting the glaciers. After the Cryogenian period, as the ice receded, Earth's climate stabilized, and life began to thrive, setting the stage for the emergence of more complex organisms during the Ediacaran period.

🧽 Sponges: Survivors of Snowball Earth

Paragraph 5 teases the story of early animals, particularly sponges, which survived the extreme conditions of Snowball Earth. These nearly indestructible creatures helped transform the oceans. The paragraph ends by inviting viewers to learn more in future episodes, thanking supporters and directing them to additional resources.

Keywords

💡Cryogenian

The Cryogenian is a geologic period that occurred approximately 716 to 635 million years ago, known as the 'Time of Ice'. It is characterized by a series of intense glaciations that led to the Earth being largely covered in ice, a scenario referred to as 'Snowball Earth'. The script discusses this period extensively as the time when the Earth underwent extreme cold conditions, leading to global freezes.

💡Dropstones

Dropstones are geological formations that provide evidence of past glaciation. They are rocks and pebbles that were transported by glaciers and eventually dropped into the ocean when the ice melted. The script mentions that dropstones are found in ancient marine formations across the globe, indicating that ice sheets extended from the poles to the tropics during the Cryogenian.

💡Magnetic particles

Magnetic particles are minerals that can align with Earth's magnetic field and are preserved in geological formations. They record the direction of the North Pole at the time of sediment deposition. The script explains how scientists use these particles to reconstruct the original positions of ocean sediments, helping to confirm the global extent of the ice sheets.

💡Carbonate rock

Carbonate rocks are formed from the weathering of other rocks and the subsequent reaction of the resulting ions with dissolved CO2 to form carbonate. The script discusses how the absence of carbonate rocks during parts of the Cryogenian indicates minimal weathering due to the Earth being covered in ice, and their reappearance corresponds to the melting of ice and resumption of weathering.

💡Rodinia

Rodinia was an early supercontinent that existed during the Neoproterozoic era. The script suggests that the breakup of Rodinia, which was particularly intense and produced a lot of basalt, disrupted the carbon cycle. This led to an increased absorption of CO2, contributing to the cooling of the Earth and the onset of 'Snowball Earth' conditions.

💡Carbon Cycle

The Carbon Cycle is the process by which carbon is exchanged between the Earth's atmosphere, crust, and oceans. The script explains that volcanic emissions release CO2 into the atmosphere, while weathering of rocks absorbs it. This cycle is crucial for maintaining Earth's temperature. During the Cryogenian, the breakup of Rodinia disrupted this balance, leading to a net absorption of CO2 and global cooling.

💡Slushball Earth

The Slushball Earth hypothesis suggests that during the Cryogenian, the Earth was not entirely frozen but had areas of open, unfrozen water at the equator where life could persist. This model is mentioned in the script as an alternative to the complete glaciation scenario, although it does not align perfectly with all geological evidence.

💡Runaway icehouse effect

The runaway icehouse effect refers to a feedback loop where the growth of ice increases the Earth's albedo, reflecting more sunlight and causing further cooling. The script describes how this effect could have made the expansion of ice sheets unstoppable once they reached below 30 degrees latitude, leading to a fully frozen Earth.

💡Franklin Large Igneous Province

The Franklin Large Igneous Province is a geological feature resulting from a massive volcanic eruption that occurred before the Cryogenian glaciations. The script mentions that this eruption released large amounts of sulfur dioxide, a gas that cools the Earth, contributing to the onset of the 'Snowball Earth' conditions.

💡Ediacara

The Ediacaran is a geological period that followed the Cryogenian. The script suggests that following the melting of the ice sheets, the oceans during the Ediacaran period became filled with a variety of animal life, indicating that life not only survived the extreme conditions of 'Snowball Earth' but also diversified.

💡Sponges

Sponges are simple multicellular organisms that are among the earliest animals. The script teases that sponges, being 'nearly indestructible', not only survived the harsh conditions of 'Snowball Earth' but may have also played a role in changing the oceans for the better, setting the stage for further animal evolution.

Highlights

The world was once entirely covered in ice, a phenomenon known as Snowball Earth.

Two global glaciations occurred during the Cryogenian period, between 716 and 635 million years ago.

Evidence for Snowball Earth is found in dropstones, which are rocks deposited by melting glaciers, showing ice existed from the poles to the tropics.

Scientists have reconstructed the positions of ancient ocean sediments using magnetic particles, confirming widespread glaciation.

The first glaciation lasted 36 million years, and the second glaciation lasted about 15 million years.

A key feature of these glaciations is the presence of carbonate rock, which disappeared during ice ages due to a lack of weathering on land.

The question remains how early life, such as cyanobacteria and sponges, survived under such extreme icy conditions.

The Carbon Cycle, which regulates Earth's climate, may have failed due to volcanic activity and the breakup of the supercontinent Rodinia.

Rodinia's breakup led to the release of large amounts of basalt rock, which absorbed carbon dioxide and contributed to global cooling.

The sun was 7% dimmer during the Cryogenian period, further contributing to Earth's cooling.

A massive volcanic eruption 18 million years before the glaciation released sulfur into the atmosphere, amplifying the cooling effect.

A runaway icehouse effect occurred, where growing ice reflected more sunlight, causing temperatures to plummet even further.

Earth eventually thawed because volcanic activity continued to release CO2, which accumulated in the atmosphere as ice prevented rock weathering.

The melting of the glaciers after the Cryogenian period led to a burst of animal life in the oceans during the Ediacaran period.

The earliest animals, like sponges, likely survived Snowball Earth due to their resilience and helped shape Earth's post-glaciation ecosystems.

Transcripts

Imagine a world covered in ice.

Estimates vary, but some scientists think at the poles, it could reach negative 130

degrees celsius.

And there was no escaping the cold even at the equator, where temperatures would have

dipped below 0 degrees.

Sheets of ice coat both land and sea, and beneath them, the world is quiet and relatively

still.

It may sound like some far-off planet, but that’s what our own planet once looked like.

And actually, it happened twice during a pair of episodes of intense glaciation between

716 million and 635 million years ago.

These global freezes occurred within that period of geologic time known as the Cryogenian,

or “Time of Ice.”

But most people refer to this chapter in our history simply as Snowball Earth.

So how did this happen?

How did the world become covered in ice?

And most importantly for us, why did the planet eventually thaw again?

Strangely enough, for both questions, the answer lies in volcanoes.

The evidence for snowball earth is written on every continent today.

Since the early 1900’s, scientists have been finding clues all over the world, in

the form of dropstones.

These are rocks and pebbles that were picked up by glaciers as they moved across the land.

And once the glaciers met the seas, icebergs broke off and floated away, carrying the rocks

with them.

When the ice melted, the stones dropped into the ocean.

These dropstones show up in ancient marine formations all over our planet.

And while the continents have shifted since the Cryogenian, scientists have been able

to reconstruct the original positions of those ocean sediments using magnetic particles preserved

in the formations themselves.

These particles record the direction of the North Pole, which tells us where on the planet

the dropstones originally fell into the sediment.

And when you reconstruct where these dropstones were deposited, you can see that they stretched

from the poles to the tropics.

Which means ice did too.

Now we know that this extensive glaciation actually happened twice between 716 and 635

million years ago.

The first episode started 716 million years ago, and lasted for about 36 million years.

And the second lasted from about 650 to about 635 million years ago.

Now, there have been glaciers on our planet before – in fact, we have some now – but

what makes these two periods so interesting is the extent of that ice.

After all, today the tropics are pretty warm – a balmy 31* C in the afternoon, which

is awfully warm if you’re trying to freeze over an ocean.

So how did our lovely temperate world get cold enough to freeze?

Well, at first, scientists thought: If there’s evidence of ice having been at the equator,

then maybe the equator wasn’t actually at the equator.

Maybe earth had been tipped over on its side at some point – which would’ve made the

equator part of the poles.

That’s how weird it was to find evidence of ice in the tropics: Scientists thought

it was more likely that Earth fell over than that the equatorial oceans had frozen.

But we now know that the evidence is too widespread for a change in Earth’s tilt to explain

it.

In fact, the evidence is so complete that it’s likely that almost all of earth froze

over, including both the equator AND the poles.

Because, in addition to dropstones, more evidence has been found, in the form of carbonate rock.

This rock is created when other rocks on the continents weather and break down to form

ions, which eventually make their way into the water.

When those ions attach to dissolved CO2, they join together to form carbonate.

And studies of ocean sediments all over the world have found that, during parts of the

Cryogenian, these carbonate rocks disappear.

Because, when the world was covered in ice, almost no weathering took place on land, so

carbonates became really rare.

But when the ice started to melt, weathering resumed -- and huge deposits of carbonates

began to form again.

Most geologists think that the absence and reappearance of these rocks is a sign that

earth was mostly to completely covered in ice.

But while that makes sense to the geologists, it doesn’t make sense to some biologists.

Life had existed on Earth for over a billion years by the time the Cryogenian started.

And organisms like photosynthetic cyanobacteria, and even animal life like sponges, had evolved

before the ice sheets grew.

Which raises the question of how early life could have survived under the ice.

Some scientists have suggested that there must have been a fair amount of open, unfrozen

water at the equator for life to persist.

This model is called Slushball Earth, but it doesn’t line up with all of the geological

evidence.

So yet another hypothesis is that there was ice everywhere, but that it was thin enough

in places for light to shine through and to allow photosynthetic life to survive.

Studies of modern cyanobacteria in Antarctica suggest that life may even have thrived on

top of the ice sheets themselves.

But whether it was thick ice, or thin ice, the ice was abundant.

So, then, why did these massive glaciations actually happen in the first place?

Well, the most popular theory is that our planet’s thermostat just … failed.

That thermostat is the Carbon Cycle – the swapping back and forth of carbon between

the atmosphere and the earth’s crust.

And it starts with volcanoes, which, over the course of thousands to millions of years,

gradually emit CO2 into the atmosphere, where it helps keep the world warm.

But CO2 levels are kept in check, because that gas gets stored in carbonate rocks during

the process of weathering.

So volcanic emissions and rock-weathering are the two counterbalances that keep earth

not too hot, and not too cold.

But in the Cryogenian, an early supercontinent known as Rodinia messed with the thermostat

by breaking up.

Breaking up is hard to do and rocks usually do it pretty violently.

But the breakup of Rodinia was especially intense, because it pumped out a lot of a volcanic

rock known as basalt.

And basalt is really, really good at soaking up CO2 in the process of weathering.

Plus, Rodinia was sitting at the equator at the time, where it was warmer and wetter,

which weathered the rock even faster.

So scientists think that this could have thrown off the carbon cycle, soaking up CO2 faster

than volcanoes could release it.

And there was another contributing factor: the sun.

During the Cryogenian, the sun was actually about 7% dimmer than it is today.

That doesn’t sound like a lot, but it was enough that, once the levels of CO2 dropped,

it was so cold that the glaciers started to grow.

And in the last few years, scientists have discovered yet another driving force behind

this phenomenon: a truly massive and spectacular eruption that took place 18 million years

before the glaciation even started.

Today, the remains of that eruption are known the Franklin Large Igneous Province: more

than a thousand square kilometers of basalt lava that cover the Canadian Arctic.

But what sets these rocks apart from others is that they were full of another planet-cooling

gas: sulfur.

When you pump sulfur into the air, it cools the earth – but normally, it doesn’t do

it for long.

Sulfur dioxide interacts with water in the atmosphere and forms acid rain, typically

leaving the atmosphere within a couple of years.

But these eruptions weren’t made by your standard volcanoes.

Instead they sprayed out huge jets of lava called fire fountains, which could have erupted

for years, spraying plumes of sulfur gases up to 12 kilometers into the atmosphere.

And that high above Earth’s surface, near the stratosphere, sulfur dioxide would take

a lot longer to break down and rain out.

So, low CO2 levels let things cool down, and a dimmer sun didn’t help.

Then suddenly, 716 million years ago, vast amounts of sulfur dioxide may have been a

final blow to earth’s thermostat - and ice began to form.

The second glaciation may have had similar causes, but it isn’t as well dated or understood

as the first.

But for both episodes, the real problem came when the ice started to grow.

Ice reflects more light than water does, which makes the world cooler, which makes more ice

grow, which makes the world even cooler – and so on.

This feedback loop is called a runaway icehouse effect.

And scientists who have modeled this process found that, once our planet had ice below

about 30 degrees latitude – the latitude of Modern-Day New Orleans -  the growing

ice was basically unstoppable.

So why are we not still stuck on a world that’s basically ... Hoth?

Because of our old friend carbon dioxide.

Rodinia didn’t stop splitting apart just because it was covered with ice.

As it kept breaking up, volcanoes kept forming and releasing CO2 into the atmosphere.

But this time, because the planet’s rocks were mostly locked beneath ice sheets, they

weren’t able to absorb all of that greenhouse gas.

So instead, it began to build up in the air.

It took almost 50 million years for enough CO2 to melt the first round of glaciers, and

about 10 to 15 million years to melt the second.

Between the two glaciations, Rodinia continued to break up near the equator - which is why

the thermostat broke twice during the Cryogenian.

But by the end of the Cryogenian, Rodinia was largely in the southern hemisphere, and

had stopped splitting so dramatically, so the thermostat could re-set itself.

Once most of the ice had melted by about 635 million years ago, the warmer oceans suddenly

began to fill with animal life.

The period that immediately followed the Cryogenian -- known as the Ediacaran period -- is full

of some strange and varied forms, descendants of the survivors of snowball earth.

But animal life itself didn’t actually first evolve in the Ediacaran.

Molecular clock analyses suggest the most recent common ancestor of all animal life

lived long before that -- some 800 million years ago.

Which means that somehow, animal life actually lived through Snowball earth.

How?

Well, the earliest animals were practically unkillable – and it turns out, they not

only survived snowball earth, they helped change oceans for the better.

But that’s a story for another time.

So come back soon to learn all about the enterprising, trail blazing, and nearly indestructible animals

that clung to life throughout the snowballs: the sponges.

Thanks to this month’s Eontologists: Patrick Seifert, Jake Hart, Jon Davison Ng, and Steve.

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Thanks for joining me today in the Konstantin Haase studio, and if you’d like to learn

more about the very deep past, then watch “The Search For the Earliest Life.”