When Trees Took Over the World

Summary

Around 420 million years ago, during the Devonian Period, plants evolved from small, moss-like forms into towering trees like Archaeopteris. Discoveries at the Gilboa quarry reshaped our understanding of early trees and the role wood played in plant evolution. Early wood helped plants stay hydrated, anchored, and grow taller, leading to the development of modern trees and influencing Earth's ecosystems. These changes lowered atmospheric CO2, shaping the land and contributing to a mass extinction. This video explores the fascinating journey of plants from algae to trees, which transformed both the atmosphere and the planet.

Takeaways

• 🌱 Plants first started covering the land around 420 million years ago, during the Devonian Period, beginning with small, moss-like plants.
• 🌲 By the end of the Devonian, large trees like Archaeopteris had spread globally, significantly transforming the planet.
• 🪵 A fossil forest in Gilboa, New York, revealed ancient tree-like plants, but they weren’t actually made of wood, altering previous assumptions about plant evolution.
• 🌍 Early wood may have evolved not for height, but to help plants retain water more effectively, especially as CO2 levels dropped.
• 💧 Plants needed water, sunlight, and CO2 to survive, but the open pores (stomata) used for absorbing CO2 also led to water loss, making water retention a major challenge.
• 🔄 Wood evolved multiple times across different plant species through convergent evolution, with roots helping plants grow taller and anchor themselves more securely.
• 🌳 Archaeopteris, one of the first true trees, could grow up to 30 meters tall and had roots that spread wide and deep, aiding in water and nutrient absorption.
• 🦠 The evolution of wood and roots contributed to more habitats for animals and increased soil generation, changing Earth's landscape and atmosphere.
• 📉 The massive decrease in atmospheric CO2, partly due to plant activity, contributed to a mass extinction event at the end of the Devonian Period.
• 🌼 By the end of the Devonian, plants had developed key traits like roots, wood, and seeds, but flowers wouldn’t appear for another 200 million years.

Q & A

What kind of plants dominated the land at the start of the Devonian Period?

At the start of the Devonian Period, around 420 million years ago, plants were small, moss-like, and rarely grew larger than a few inches.

What was the significance of the discovery at Gilboa, New York?

In the 1920s, workers at a quarry in Gilboa, New York, uncovered sandstone casts of ancient trees dating back 390 million years. This 'fossil forest' significantly influenced how scientists viewed the evolution of plants.

Why was the earlier hypothesis about the evolution of wood challenged in 2010?

In 2010, new discoveries at Gilboa revealed that some of the ancient trees weren't actually made of wood, leading scientists to rethink the earlier hypothesis that wood evolved primarily to help plants grow taller and reach sunlight.

What role did wood play in the earliest land plants?

The earliest wood likely evolved to help plants retain water. As plants needed to keep their stomata open longer to absorb carbon dioxide, wood became a mechanism for transporting water more effectively.

How did wood evolve in plants during the Devonian Period?

Wood evolved independently at least five different times across different plant families by the Late Devonian. It helped plants anchor themselves more solidly, grow taller, and exploit new ecological niches.

What reproductive adaptation did some plants develop as they began to rely less on wet environments?

Plants like Archaeopteris began to reproduce with male and female spores, with the female spores being larger and storing a food supply for the embryo. This development is thought to be a precursor to seeds.

Why is Archaeopteris considered one of the earliest modern trees?

Archaeopteris, appearing around 370 million years ago, is considered one of the earliest modern trees because it grew up to 30 meters tall, had woody tissue, and its roots spread deep, helping it anchor and gather water efficiently.

What environmental impacts did Devonian plants have on the planet?

Devonian plants, like Archaeopteris, changed the environment by stabilizing sediment with their roots, creating habitats, breaking down rocks to release minerals, and increasing soil production. This also contributed to a drastic reduction in carbon dioxide levels.

How did the rise of trees in the Devonian Period affect the planet's atmosphere?

The rise of trees, which pulled large amounts of carbon dioxide out of the atmosphere, contributed to a significant drop in CO2 levels during the Devonian Period. This likely played a role in the mass extinction event at the end of the Devonian.

What traits had plants developed by the end of the Devonian Period to thrive on land?

By the end of the Devonian Period, plants had developed essential traits like roots, wood, leaves, and seeds, which allowed them to thrive on land. These adaptations helped shape the modern ecosystems we see today.

Outlines

00:00

🌱 The Early Devonian Forest Mystery

Around 420 million years ago, at the beginning of the Devonian Period, plants were small and moss-like, but by the end of the period, large trees like Archaeopteris had emerged, changing the landscape forever. This transformation puzzled scientists for decades until a 2010 excavation in Gilboa, New York, revealed that the early 'trees' discovered there weren’t made of wood. Instead, the forest was covered with roots of non-tree plants that had wooden roots, showing that paleobotanists had been overlooking a key part of plant evolution: the ground. The evolution of wood and the dominance of trees were critical in shifting Earth’s ecosystem from algae to land-dwelling trees.

05:01

🌍 Early Land Colonization and the Role of Xylem

Plants first began colonizing the land during the Ordovician period, about 470 million years ago. These early plants had to adapt to dry, nutrient-poor environments, leading some to either remain in wet habitats or develop strategies to survive dehydration. By the mid-Devonian, plants had developed vascular tissue called xylem to transport water. Some plants, despite being small, had evolved wood-like structures with multiple layers of xylem, allowing them to transport water more effectively. This adaptation was crucial because it helped plants manage their water needs in an environment where carbon dioxide levels were dropping, forcing plants to keep their pores (stomata) open longer to absorb CO2, leading to more water loss.

🌳 The Evolution of Wood and Water Conservation

The development of wood, with its cellulose fibers and lignin, gave plants the ability to transport water more efficiently, which was essential in the Devonian’s drying climate. Woody tissues allowed plants to stay hydrated, and this adaptation evolved independently at least five times, showcasing convergent evolution. As more plants evolved wood, they began to exploit new ecological niches, growing taller and more stable with stronger root systems. Additionally, the reproductive strategies of plants were changing, as wood allowed them to thrive in less wet environments. Archaeopteris, a significant Devonian tree, reproduced with spores, but its larger female spores resembled seeds, making it more adaptable.

🌲 Archaeopteris and the Transformation of Devonian Landscapes

Archaeopteris, one of the earliest true trees, grew to be 30 meters tall and spread its roots deep into the ground. Its fossils are found on every continent, including Antarctica, indicating its global dominance. The roots of Archaeopteris and other Devonian plants broke down rocks and stabilized soils, which helped form meandering rivers and fertile habitats for animals. Their woody tissues contributed to the formation of soil, especially humus, which played a key role in nutrient cycling. The increasing plant activity significantly reduced atmospheric carbon dioxide levels, which, while beneficial for the land ecosystem, contributed to a mass extinction event in the oceans by the end of the Devonian.

🌍 How Devonian Trees Shaped Our World

The Devonian trees, like Archaeopteris, were instrumental in shaping the modern world. Their roots broke down rocks, creating soil, while their carbon consumption drastically reduced CO2 levels in the atmosphere. Although this contributed to the end of the Devonian world through a mass extinction, these trees set the stage for future ecosystems to thrive. By the end of the Devonian, plants had developed essential traits for their continued success, including roots, wood, leaves, and seeds. These adaptations helped them dominate the land and lay the groundwork for the next major plant innovation: flowers, 200 million years later.

📱 Thanks to Trees, and Eons is on TikTok!

The impact of trees on our world is immeasurable, and while humans and mammals have changed the planet, the groundwork laid by trees was crucial. The video ends with a note of thanks to trees and an announcement that Eons is now on TikTok. The platform will feature short stories about geological history, with fun perks for supporters like joke submissions. As a fun conclusion, the host shares a viewer’s joke about archaeopteryx catching the worm, tying it all together with a bit of humor and appreciation for the natural history of trees.

Keywords

💡Devonian Period

The Devonian Period occurred about 420 to 360 million years ago and was a critical time for the evolution of plants. During this period, plants evolved from small, moss-like organisms to the first giant trees. This era is essential in the video's theme as it marks a dramatic transformation in plant life on Earth, laying the foundation for modern ecosystems.

💡Archaeopteris

Archaeopteris was a tree-like plant from the Devonian Period, notable for its wood and advanced reproductive strategies. It represents one of the earliest forms of trees, growing up to 30 meters tall, and played a significant role in transforming Earth's landscapes. In the video, it's highlighted as an example of how wood evolution allowed plants to spread and dominate new environments.

💡Gilboa Fossil Forest

The Gilboa Fossil Forest, discovered in New York, contains some of the oldest known fossilized trees dating back 390 million years. Initially, scientists thought these trees were made of wood, but later discoveries revealed they weren't. This forest is pivotal in understanding plant evolution, as mentioned in the video, showing that paleobotanists should have focused on plant roots to understand tree development.

💡Xylem

Xylem is a type of vascular tissue in plants that transports water from roots to leaves. It plays a crucial role in plant survival, especially during the Devonian when plants needed to retain water in harsh environments. The video emphasizes that xylem was a key development in plants, eventually leading to the evolution of wood.

💡Lignin

Lignin is an organic polymer found in the cell walls of plants, providing strength and rigidity, especially in wood. Its presence allowed plants to grow larger and more robust. In the context of the video, lignin is essential to the evolution of woody plants, helping them retain water and grow taller, which changed Earth’s ecosystems.

💡Convergent Evolution

Convergent evolution refers to the independent evolution of similar traits in different species. The video notes that wood evolved at least five times across different plant families during the Late Devonian, showcasing how similar environmental pressures led multiple plant groups to develop wood as an adaptation.

💡Stomata

Stomata are small pores on the surface of plant leaves that allow gas exchange, including the absorption of carbon dioxide and the release of water vapor. The video highlights the importance of stomata during the Devonian, as plants needed to balance water loss with carbon dioxide intake for photosynthesis, driving the evolution of wood to help with water retention.

💡Gymnosperms

Gymnosperms are a group of seed-producing plants, including conifers, that are thought to have evolved from earlier plants like Archaeopteris. The video mentions gymnosperms in the context of how plants transitioned from spore-based to seed-based reproduction, which allowed them to spread into drier environments.

💡Spores

Spores are reproductive cells that plants release to grow new organisms. Early plants relied on moist environments for their spores to successfully germinate. In the video, the evolution from spore-based reproduction to more advanced seed-based methods is highlighted as a key development during the Devonian, allowing plants to spread further.

💡Mass Extinction

Mass extinction refers to a widespread and rapid decrease in the biodiversity on Earth. The video briefly touches on the mass extinction event at the end of the Devonian Period, where the rise of trees and plants significantly altered the atmosphere, contributing to the extinction of many marine species.

Highlights

Around 420 million years ago, plants were just starting to cover the land, beginning as small, moss-like forms.

By the end of the Devonian, giant trees like Archaeopteris had spread around the world, transforming the environment forever.

In the 1920s, workers in a quarry at Gilboa, New York, uncovered ancient fossilized tree casts, reshaping scientists' understanding of plant evolution.

In 2010, new findings revealed that these 'trees' were not trees at all—they weren’t made of wood, upending prior theories.

Discovery of wood-like roots on non-tree plants led scientists to understand that the evolution of trees required looking down, at their roots, not up.

Early plants began colonizing land about 470 million years ago, facing harsh, dry conditions with low nutrients.

The development of xylem in plants helped transport water from the bottom to the top, crucial for survival in drier environments.

Wood initially evolved as a mechanism for keeping plants hydrated, allowing for more effective water transportation.

Wood evolved independently at least five different times in various plant families during the Late Devonian period, a clear case of convergent evolution.

Plants like Archaeopteris, which appeared around 370 million years ago, were among the first true trees and could grow up to 30 meters tall.

Woody roots anchored plants securely into the soil, allowing them to grow taller and exploit new environmental niches.

The development of male and female spores in plants like Archaeopteris represented an evolutionary precursor to seeds.

Plants like Archaeopteris created habitats for animals, breaking down rocks and stabilizing sediment to create meandering rivers and nutritious soil.

By the end of the Devonian, trees and plants had pulled massive amounts of CO2 from the atmosphere, contributing to a mass extinction event.

Plants developed almost all the necessary adaptations—roots, wood, leaves, and seeds—by the end of the Devonian, setting the stage for future plant evolution.

Transcripts

Around 420 million years ago, at  the start of the Devonian Period,  

plants were juuuust starting to cover the land.  

They were small and kind of moss-like,  and rarely grew larger than a few inches.

But by the end of the Devonian, 60  million years later, giant trees,  

like Archaeopteris, had spread around  the world - and changed it, forever.

And figuring out how that happened started  in the 1920s at a quarry in Gilboa, New York,  

where workers uncovered something surprising.

Buried among the rocks and dirt were  sandstone casts of what looked like  

ancient trees dating back 390 million years.

This “fossil forest” influenced how scientists  viewed the evolution of plants for decades.

You see, previously, they thought that  the evolution of wood was a key  

adaptation that was linked to being able  to reach sunlight. As species diversified,  

having wood helped plants grow taller and break  through the canopy created by their competitors.

But in 2010, a new excavation at Gilboa  threw a wrench in this old hypothesis.

Those so-called ancient trees weren’t  actually trees at all - because they  

weren’t made of wood, which is one of  the things that makes a tree a tree.

But the forest floor was covered with roots  from a different plant - one that didn’t look  

like a tree at all...except  its roots were made of wood.

So, instead of looking up to learn  about the evolution of trees, it turns  

out paleobotanists should’ve  been looking down all along.

The discoveries made in that ancient forest  have sent scientists down a twisting path  

to understand how our planet went from  the reign of algae to the rule of trees.

Plants first began colonizing the land during the  Ordovician period, about 470 million years ago.

And these earliest plants had a lot  to adapt to in this new environment.  

The land was harsh, dry, and poor in nutrients.

This left the early plants with two options: live  somewhere that was wet all the time, like a swamp,  

or let their water content vary with  their surroundings and develop the  

ability to recover from being  almost entirely dried out.

And while there are plants today  that use this second option,  

sometimes called “resurrection plants,” it’s  really hard on a plant’s metabolism. So,  

for a long time, most plants remained  very small and pretty flimsy.

But things started to change about a  quarter of the way into the Devonian Period.

We know this because in 2011, researchers reported a new species of  plant dating back to 407 million years ago,  

almost 20 million years older than  the woody plants of the Gilboa forest.

By this time, many plants had developed  a kind of vascular tissue called “xylem.”  

This helped move water from the  bottom to the top of the plant.

And pro-tip, xylem is one of my favorite scrabble words.

If you play it right you're looking at 30 points at least.

But that new species of plants had  more than one layer of xylem - it had  

what’s called secondary xylem, also known as wood.

Wood consists of cellulose fibers and a compound called lignin,  an organic polymer.

Lignin and cellulose are major components  of the cell walls of land plants,  

giving them structure and support, and  together, they’re what makes wood so tough.

Although these plants would probably  have grown just a little higher than  

your ankles - they still spent energy  on creating wood-like structures.

So if these plants were so small then why bother with wood at all?

Well, probably to keep from getting thirsty.

The earliest wood seems to have been a mechanism for transporting water more effectively

than one layer of xylem could on its own.

Because, at this point in the Devonian,  holding onto water was a real challenge.

Stop me if you've heard this before but

plants need water, sunlight,  and carbon dioxide to photosynthesize,  

and they absorb that carbon dioxide  through pores called stomata.

But those pores also allow  for the evaporation of water.

And! In the early Devonian, the concentration of  carbon dioxide in the atmosphere was going down,  

so plants needed to keep their stomata open  for longer to absorb all the CO2 they needed.

And, with those pores open longer, more water could escape.

The development of wood was becoming an excellent  strategy for keeping the whole plant hydrated,  

because it’s really good at conducting water.

So woody tissues seems to have first appeared as  an adaptation for keeping plants hydrated.  

But plants didn’t stop there.

It’s now thought that wood evolved at least five  

different times across different  families by the Late Devonian.

It’s a pretty clear case of convergent evolution,  

and as more plants developed this structure,  they started exploiting new niches.

Woody roots helped plants anchor themselves more  

solidly into the earth and  allowed them to grow taller.

And at the same time as plants  were developing woody tissues,  

they were also making a few more modifications.

When early plants first came onto land,  most of them reproduced by releasing spores.

This meant that they were really  dependent on a wet environment,  

otherwise the spores would fail to grow - the  different reproductive cells they contained  

needed a thin layer of water on the plant’s  surface to move around and come together.

But once wood helped plants stay hydrated,  some plants didn’t need to rely quite so  

much on wet landscapes - and they began  developing different ways to reproduce.

Take, for example, that plant I mentioned  earlier: Archaeopteris from the late Devonian.  

Its name means “early fern,” but  that isn’t entirely accurate.

It was actually something between  a fern and a group of woody plants  

that exists today called gymnosperms,  which includes conifers and gingkos.

And it reproduced like ferns do, with spores  - but it had both male and female spores,  

making it unique among its peers at the time.

The female spores were bigger and  stored a food supply for the embryo,  

so they’re thought to be a precursor to seeds.

And this helped Archaeopteris spread around the planet,  

by making its reproduction even less  

dependent on perfect  environmental conditions.

Fossils of Archaeopteris have been found  on every continent, including Antarctica.

It's considered one of the earliest modern  trees, appearing around 370 million years ago,  

and it could grow to be 30 meters tall, which  made it a giant of the Devonian forests.

And unlike those plants found at Gilboa  that were originally mistaken for “trees,”  

even though they didn’t have true woody  tissue, Archaeopteris was full of the stuff.

Their roots spread deep and wide, allowing for  more effective collection of water and nutrients.

And Archaeopteris and other Devonian plants also  created more habitats for animals, and more food  

for them, too. And their roots broke down rocks,  releasing new minerals into bodies of water.

At the same time, the root systems  of all this vegetation created more  

stability in the sediment, which  allowed meandering rivers to form.

The cycle of decay and renewal of these plants  increased the amount of nutritious soil available.  

And the wood in these plants was  directly responsible for a lot  

of the soil generation that  took place in the Devonian.

The organic component of soil, called humus,  is mostly made up of broken down lignin.

And between the weathering of rocks and the amount  of carbon dioxide that the trees pulled out of the  

atmosphere, CO2 levels fell drastically from  the beginning of the Devonian to the end.

This, admittedly, was not great for a lot of  the species living in the oceans at the time.  

It was probably actually a major cause of the  mass extinction that happened at the  

end of the Devonian...which  really deserves its own episode.

But the thing is, these trees directly  created the world that we live in today,  

by changing both the atmosphere and the land.

So, while they helped end  the world of the Devonian,  

if it wasn’t for them, our world  might not have gotten started.

By the end of the Devonian period,  

plants had developed almost all of  the traits they would need to thrive.

It would take another 200 million years for the  next big plant innovation to appear: flowers.

So from the false trees of the  Gilboa forest,  

to the true trees like Archaeopteris, it’s  

clear how big a difference the evolution  of wood made in helping trees take over.

And once plants were using seeds to reproduce - 

- they had the handful of adaptations that made  them mostly modern: roots, wood, leaves and seeds.

So while we might think that it’s humans, or at  least mammals, that have transformed the world  

the most, there’s a chance we might not even be  here without the trees had not put in the work first.

So thanks trees for giving us a planet we can actually live on

Guess what?! Eons is now on TikTok! It's one of my favorite things.

We’ll  be posting short stories from deep time,

casual geology in the outdoors, and  more!

You can find us at @PBSEons.

And thanks to this month’s  treemendous Eontologists:  

Sean Dennis, Jake Hart, Annie & Eric Higgins,  John Davison Ng, and Patrick Seifert!

Become an Eonite at patreon.com/eons and  you can get fun perks like submitting  

a joke for us to read, like  this one from Steph....ok brace yourselves: Why did  

the archaeopteryx catch the worm? - Because it was  an early bird (I’m so sorry). You should be sorry,  

Steph! Early bird gets the worm...I get it.

And as always thanks for joining me in

the Konstantin Haase studio. Subscribe at  youtube.com/eons for more evolutionary escapades.