When Trees Took Over the World
Summary
TLDRAround 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
🌱 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.
🌍 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.
Mindmap
Keywords
💡Devonian Period
💡Archaeopteris
💡Gilboa Fossil Forest
💡Xylem
💡Lignin
💡Convergent Evolution
💡Stomata
💡Gymnosperms
💡Spores
💡Mass Extinction
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.
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