The World Before Plate Tectonics

Summary

Around 2 billion years ago, Earth was vastly different with extreme conditions and limited life. The 'Boring Billion' period, from 1.8 to 800 million years ago, was actually pivotal for the emergence of modern plate tectonics and the rise of complex life. Despite the mantle's high temperatures hindering deep subduction, early lithospheric movements led to the formation of supercontinents like Nuna and Rodinia. This era, marked by sulfur-rich oceans and microbial life, laid the groundwork for Earth's biodiversity and habitability, setting the stage for the Cambrian explosion.

Takeaways

• 🌍 Around 2 billion years ago, Earth was radically different with extreme conditions and a stable climate.
• 🌊 The ancient oceans were inhospitable to most modern animal life due to low oxygen and high sulfur levels.
• 🌿 Sparse life forms on land were mainly microbial, such as cyanobacteria and possibly lichens.
• 🔥 The Earth's interior was hotter, and the mantle was too hot to allow for modern plate tectonics.
• 🌐 The supercontinent formed during this period was called Nuna, existing around 1.8 billion years ago.
• 🌬️ The term 'Boring Billion' refers to the period from 1.8 billion to 800 million years ago, characterized by stability.
• 🌋 The beginning of modern plate tectonics is marked by the breakup of Rodinia, possibly as recent as 750 million years ago.
• 🦠 Life during the Boring Billion consisted mostly of prokaryotes, such as archaea and photosynthetic bacteria.
• 🌳 The rise of eukaryotic life is marked by fossils in China dating back 1.7 billion to 1.4 billion years ago.
• 🌿 The Cambrian explosion, a significant diversification of life, was set up by the changes in Earth's tectonic activity.
• 🌎 Plate tectonics have been crucial in shaping Earth's habitability and the diversity of life forms we see today.

Q & A

How was Earth different around 2 billion years ago?

Around 2 billion years ago, Earth was characterized by extreme conditions. Oceans were inhospitable to most animal life due to low oxygen and high sulfur levels. Land had limited life forms, mostly microbial organisms like cyanobacteria and possibly lichens. The Earth's interior was also more extreme, with a stable climate, minimal glacial activity, and a sun that was 5 to 18% less powerful than it is today.

Why were the oceans inhospitable to most animal life at that time?

The oceans were inhospitable because they were very low in oxygen but really high in sulfur, making them unsuitable for most animal life that exists today.

What was the term geologists used to describe the period from about 1.8 billion to 800 million years ago?

Geologists once called the period from about 1.8 billion to 800 million years ago the 'Boring Billion' due to its remarkable stability and lack of significant geological activity.

How did the early Earth's climate during the Boring Billion differ from today's?

During the Boring Billion, the climate was remarkably stable with little glacial activity and a sun that was significantly less powerful. This stability contrasted with the dynamic climate and active geological features we see on Earth today.

What evidence do geologists have of the Earth's early plate tectonics?

Geologists have evidence from surviving rock slabs and computer models that suggest the Earth's lithosphere was active around 2.78 billion years ago with supercontinents breaking apart and forming, mountain-building episodes, and metamorphism.

Why do some geologists debate whether the late Archean subduction counts as the first plate tectonics?

Some geologists debate this because the subduction was different from today's, with a hotter mantle making the crust thin and weak, leading to shallow subduction. This was a different 'flavor' of subduction, not like the deep subduction we see today.

What was the significance of the supercontinent Nuna?

The supercontinent Nuna, formed by 1.8 billion years ago, was significant as it was a result of the early movements of the lithosphere that helped separate the crust into plates, leading to the formation of this supercontinent during the Boring Billion.

How was life on Earth different during the Boring Billion compared to today?

During the Boring Billion, life on Earth was mostly prokaryotic, with organisms like archaea and photosynthetic bacteria thriving in sulfur-rich waters. In contrast, today's life forms are predominantly eukaryotic, with complex multicellular organisms.

What was the condition known as euxinia, and why was it significant?

Euxinia is a condition characterized by very low oxygen and high hydrogen sulfide levels in the ocean, which is toxic to most eukaryotes. It was significant because it dominated the oceans around 2 billion years ago, shaping the types of life that could thrive during that period.

How did the cooling of the Earth's mantle affect plate tectonics?

The cooling of the Earth's mantle led to the formation of more rigid plates that could interact more effectively, forming rift valleys and subduction zones. This change marked the beginning of modern plate tectonics, with evidence of deep subduction and the formation of metamorphic minerals under high pressure.

Why is plate tectonics considered important for the diversification of life on Earth?

Plate tectonics is important for the diversification of life because it can create new habitats and destroy others, promoting biodiversity. It also impacts ocean circulation, climate, and carbon cycling, which are crucial for shaping life on Earth.

Outlines

00:00

🌏 Early Earth's Extreme Conditions

The script describes Earth around 2 billion years ago, highlighting its extreme conditions. Oceans were inhospitable due to low oxygen and high sulfur levels, while land was sparsely populated by microbial life such as cyanobacteria and possibly lichens. The Earth's interior was hotter, and the mantle prevented modern plate tectonics, keeping the continental plates bound together in a supercontinent. This period, known as the Boring Billion, was actually pivotal for the development of modern plate tectonics and the rise of life. The script explains the importance of plate tectonics in shaping Earth's features, such as the Himalayas and the Pacific Ring of Fire, and how geologists study ancient rocks to understand the past.

05:05

🦠 Prokaryotes and the Boring Billion

Paragraph 2 discusses the dominance of prokaryotes during the Boring Billion, a period that was actually crucial for the evolution of complex life. Despite the challenging conditions of low oxygen and high hydrogen sulfide in the oceans, simple life forms like archaea and photosynthetic bacteria thrived. The script mentions the discovery of eukaryote fossils in China dating back 1.7 to 1.4 billion years, indicating the beginning of more complex life. It also explains how the Earth's physical changes, including the cooling of the mantle and the breakup of supercontinents like Rodinia, led to the development of modern plate tectonics and increased biodiversity. The paragraph concludes by emphasizing the importance of plate tectonics in creating the diverse ecosystems we see today.

10:09

🎥 Joining Eons in the Studio

The final paragraph is a brief invitation for viewers to join the Eons channel on YouTube for more content about deep time. It serves as a call to action for viewers to subscribe and engage with the channel for further exploration of Earth's history.

Keywords

💡Archean Eon

The Archean Eon is the earliest part of Earth's history, spanning from about 4 billion to 2.5 billion years ago. It represents the period when the Earth was first forming and stabilizing. In the video, the Archean Eon is mentioned as a backdrop to understand the early conditions of the planet, highlighting the transition from its formation to the beginning of modern plate tectonics.

💡Plate Tectonics

Plate tectonics refers to the movement of Earth's lithosphere, which is divided into several large plates that float on the semi-fluid asthenosphere below. The video discusses how plate tectonics has shaped Earth's landscape, including the formation of mountains, rift valleys, and volcanic activities. It also explores the differences between early plate tectonics and the modern version.

💡Subduction

Subduction is a geological process where one tectonic plate moves under another and sinks into the mantle. This process is a key driver of plate tectonics and is discussed in the context of the evidence for the beginning of plate tectonics on Earth. The video mentions how subduction has changed over time, with early subduction being shallow compared to the deep subduction of today.

💡Supercontinent

A supercontinent is a landmass consisting of multiple continents that have combined together. The video discusses how supercontinents like Nuna and Rodinia formed and later broke apart, which is a critical part of the plate tectonics process. These events are significant as they led to the distribution of life and the changes in Earth's climate and geography.

💡Euxinia

Euxinia refers to a condition in water bodies where there is a high concentration of hydrogen sulfide and very low levels of oxygen, which is toxic to most eukaryotic life. The video explains that around 2 billion years ago, the Earth's oceans were likely in a state of euxinia, creating a challenging environment for the development of complex life forms.

💡Prokaryotes

Prokaryotes are simple, single-celled organisms without a nucleus or other membrane-bound organelles. The video highlights that during the 'Boring Billion' period, most life on Earth consisted of prokaryotes like archaea and cyanobacteria, which were able to thrive in the sulfur-rich and low-oxygen conditions of the time.

💡Boring Billion

The 'Boring Billion' is a term used by geologists to describe the period from about 1.8 billion to 800 million years ago, characterized by a stable climate and limited geological activity. The video challenges this notion by explaining how this period was crucial for the development of modern plate tectonics and the rise of life, setting the stage for the Cambrian explosion.

💡Cyanobacteria

Cyanobacteria are photosynthetic bacteria that played a significant role in the Earth's early ecosystems. The video mentions cyanobacteria as one of the few life forms that existed on land during the 'Boring Billion' period, contributing to the sulfur cycle and being an important component of the early biosphere.

💡Mantle

The mantle is the layer of the Earth between the crust and the core, made up of solid rock that behaves plastically over long periods of time. The video discusses how the temperature of the mantle has changed over Earth's history, affecting the thickness and movement of the tectonic plates. The cooling of the mantle is linked to the development of modern plate tectonics.

💡Seafloor Spreading

Seafloor spreading is the process by which new oceanic crust is formed at mid-ocean ridges as tectonic plates move apart. The video explains that seafloor spreading is a result of plate tectonics and contributes to the creation of new habitats and the diversification of life. It is an ongoing process that shapes the Earth's海底地形.

💡Hydrothermal Vents

Hydrothermal vents are openings in the Earth's crust from which issue hot water and minerals. The video mentions hydrothermal vents as areas of high biodiversity, particularly rich in iron and silica, which serve as important nutrients for many life forms. These vents are formed due to the movement of tectonic plates and are considered oases of life in the deep sea.

Highlights

Around 2 billion years ago, Earth was a very different place with extreme conditions.

The oceans were inhospitable to most animal life due to low oxygen and high sulfur levels.

Land life was scarce, with only microbial organisms like cyanobacteria and possibly lichens.

Earth's interior was more extreme, with higher temperatures compared to today.

The climate was stable with no glacial activity and a weaker sun.

Modern plate tectonics had not yet begun; the mantle was too hot, creating a supercontinent.

The Boring Billion period was marked by stability but was crucial for the rise of life and plate tectonics.

Today's active plate tectonics cycle shapes Earth's most noticeable features.

Evidence of the oldest rocks is limited due to continuous recycling and destruction.

Archean rocks that survived are found worldwide, some over 3 billion years old.

Subduction is a key driver of today's plate tectonics, indicating its ancient beginnings.

Around 2.78 billion years ago, there is evidence of Earth's lithosphere being active with supercontinents forming and breaking apart.

The high mantle temperatures in the Archean made the crust thin and weak, unlike today's plate tectonics.

The early movements of the lithosphere led to the formation of the supercontinent Nuna.

2 billion years ago, the ocean was low in oxygen but abundant in hydrogen sulfide, creating toxic conditions.

Prokaryotes thrived in the sulfur-rich environment during the Boring Billion.

Geobiologists find the Boring Billion significant as it marked the beginning of complex eukaryotic life.

Rock formations in China contain fossils of eukaryotes dating back 1.7 billion to 1.4 billion years ago.

Life on the early supercontinent was limited to microbes and slimy mats in sulfur-rich water.

The breakup of Rodinia and the cooling mantle led to the beginning of modern plate tectonics.

Experts debate whether the earlier period of subduction counts as the beginning of plate tectonics.

Plate tectonics has shaped Earth into a habitable world and may have been crucial for the diversification of life.

Seafloor spreading, a result of plate movement, creates new habitats and promotes biodiversity.

The Boring Billion was a period of settling down for Earth, preparing for its next big move.

Earth's plate tectonics might have been essential for the evolution of complex life forms.

Transcripts

Around 2 billion years ago, Earth was a very different place.

Pretty much everything was more extreme than it is today, from ocean chemistry, to slimy

life on land, to the position of landmasses. Things were generally… a little weird.

The oceans would have been inhospitable to most animal life today, because they were

very low in oxygen but really high in sulfur.

Meanwhile, on land, there wasn’t much life to speak of, except for microbial organisms,

like cyanobacteria and possibly lichens.

Even the temperature inside the Earth was more extreme than it is today.

But the world for these early living things was also kind-of...boring.

The climate was remarkably stable; there wasn’t much glacial activity, and the sun was 5 to

18% less powerful than it is today.

Even the rocks under the microbes were fairly stable.

Modern plate tectonics, the movement of rock plates on top of Earth’s mantle, hadn’t

gotten started yet.

The mantle was just too hot, so it bound the continental plates together into a supercontinent.

And the plates were flimsy and thin.

Because this time in Earth’s history was so stable, geologists once called it the Boring

Billion - the billion years from about 1.8 billion to 800 million years ago.

But the fact is, this period was anything but boring. In fact, it set the stage for

our modern version of plate tectonics - and probably for the rise of life as we know it.

Today, Earth’s plate tectonics cycle is active.

The plates move around, forming mountains as they smash together, shallow seas when

they rift apart, and even volcanoes when they slide under each other.

Plate movement is responsible for some of Earth’s most noticeable features, including

the Himalayas, the East African Rift valley, and the Pacific Ring of Fire.

They’re so important that it’s almost hard to imagine what the planet looked like

before plate tectonics.

To figure that out, we have to go back to when Earth was first settling down from its

formation, back at the end of the Archean Eon, almost 3 billion years ago.

Unfortunately for geologists, a lot of the rock record has been continuously recycled

and destroyed through subduction, where one slab of rock slides under another and dives

down into the mantle, where it melts.

That means evidence of the oldest rocks is really limited, because they’ve been ripped

apart, smashed together, and eroded away.

But the Archean rocks that did manage to survive on Earth’s surface are spread out

all over the world, in places like North America, Australia, Africa, and Eastern Europe - and

some are more than 3 billion years old!

And that presented a puzzle to geologists who wanted to find out when modern plate tectonics

started, and what it looked like.

Since subduction is one of the main drivers behind today’s plate tectonics, they looked

for evidence of subduction as a sign of the beginning of ancient plate tectonics.

So scientists slowly pieced together evidence from the few surviving rock slabs, as well

as computer models, to start to understand the Archean.

You see, geologists can look at minerals in a rock to figure out how deep a piece of land

went into Earth’s interior, and how hot it got.

And they found that starting around 2.78 billion years ago, in the late Archean, there is solid

evidence that Earth’s lithosphere was busy.

There were supercontinents breaking apart and forming, mountain-building episodes, and

metamorphism, where rocks are transformed by high heat and pressure.

Now, that certainly sounds a lot like plate tectonics, but does it really count as the

first example of plate tectonics? Well, geologists have opinions about that.

It didn’t work the same way as the modern version of plate tectonics because Earth’s

mantle was hotter than it is today -- about 250 degrees celsius hotter.

The mantle reached peak temperatures in the Archean, and has been slowly cooling since

then. 2.8 billion years ago, the mantle was still holding on to more heat than it is today.

Those high mantle temperatures made the crust thin, weak, and easy to deform - like cookies

straight out of the oven. The metamorphic rock record shows that if there was subduction

into the mantle, the sinking crust stayed pretty shallow, unlike today.

It was a different “flavor” of subduction. That’s why some geologists don’t think

this really counts as the first evidence of plate tectonics.

But these early movements of the lithosphere helped separate the crust into plates.

Those plates crammed together in one spot, leading to the formation of the  supercontinent

Nuna by 1.8 billion years ago.

Welcome to the so-called Boring Billion.

Remember, all of this was over a billion years before the Cambrian explosion. So with the

exception of some microbes, there was no life on land: it was confined to the ocean.

And the ocean was very different than it is now.

2 billion years ago, it’s likely that most of the ocean was very low in oxygen.

But what it did have in abundance was hydrogen sulfide. And by 1.6 billion years ago that

combination created a condition known as euxinia, which is toxic to most eukaryotes -- organisms

that have an enclosed nucleus in each cell.

But the prokaryotes, simpler life forms that don’t have an enclosed nucleus, made the

best of their strange environment.

Microscopic life forms like archaea were perfectly happy. And so were bacteria, like cyanobacteria,

which were photosynthetic and could metabolize the abundant sulfur in the ocean.

Also there were purple and green sulfur bacteria, which are brightly-colored photosynthetic

microbes that can form squishy mats in aquatic environments.

They sound like they belong in a scifi movie, but they’re very real, and still around

today.

So most of the life found in the Boring Billion was prokaryotic. And with all this sulfur

in the environment, researchers think this period was the stinkiest time on Earth!

But to geobiologists - scientists who study the interactions between the biosphere and

Earth’s physical processes - this period was never boring, because it marked the beginning

of complex eukaryotic life.

For example, in China there are rock formations that contain fossils of eukaryotes that date

back 1.7 billion to 1.4 billion years ago!

The majority of these organisms lived in water, including protists and other early eukaryotes,

So life on the early supercontinent, with limited plate movement, was doing okay. But

it was still all microbes and slimy mats, trying to survive in sulfur-rich water.

So how did we get from there to here, or even to the Cambrian explosion?

Well, life needed Earth to shake things up.

And that didn’t happen in the Boring Billion, at least not enough to make a huge difference.

The old flavor of softer, squishier plate tectonics continued, with minor, shallow subduction

around Nuna and the next supercontinent, Rodinia.

Plates on the outside of the supercontinent were mostly stagnant, but started sinking

into the mantle, which was beginning to cool.

Then, probably no later than 750 million years ago, during the breakup of Rodinia,

the cooler mantle meant that the plates weren’t continuously melting and sticking together.

Separate slabs of rock could interact, forming rift valleys and subduction zones.

Some geologists say this was the beginning of modern plate tectonics, because they have

clear evidence of deep subduction.

For example, they’ve found metamorphic minerals that could only have formed at high pressure,

deep in Earth’s mantle.

And that would’ve been impossible under the earlier type of plate tectonics, when

the plates stayed shallower and softer.

So, experts are still debating whether the earlier period of subduction really “counts”

as the beginning of plate tectonics. And some say that there was even older evidence of

tectonic movement, as far back as 4 billion years ago!

But there’s one thing that they all agree on: plate tectonics helped shape the planet

into the habitable world we know today.

As supercontinents like Rodinia broke up into separate plates, the slabs jostled each other,

smashing together or moving apart.

When two plates separate from each other, oceanic ridges form - underwater mountain

ranges where hot magma constantly comes out and cools, becoming part of the plates. This

process is called seafloor spreading.

Today, seafloor spreading is occuring in several ocean basins, and oceanic ridges are some

of the best places to find hydrothermal activity, where water interacts with hot, fresh, ocean

crust.

These vents are hotspots for biodiversity, especially because they are so rich in iron

and silica, important fertilizers for many life forms.

And moving plates can constantly create new

habitats and destroy others, which promotes rapid diversification of life.

Researchers have shown that biodiversity increases really fast when there’s more continental

fragmentation.

Plus, the arrangement of the continents can impact ocean circulation, climate, carbon

cycling, and many of the other processes that help shape life on Earth.

So it turns out that the Boring Billion wasn’t really boring at all! Earth was just settling

down and getting ready for its next big move.

And today, we’re the only planet known to have this type of plate tectonics.

So, while the movement of continental plates can be destructive, it might’ve also been

pretty important for pushing life past the squishy microbe stage to create the lush,

complex diversity of living things that we know today.

If you’re a fan of Eons, then you’ll love the new PBS three-part natural history series:

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