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0:02Every tree you have ever seen is dead.
0:05It turns out the alive part of a tree is
just a tiny, paper thin strip of cells,
0:10trapped between a dead skeleton and dead outsides.
0:13Trees are some of the most extreme beings on
earth with one of the most unique strategies in
0:19nature – on top of being mostly dead stuff, they
forge their body out of thin air, they mercilessly
0:25crush rocks with acid, and they have an internal
negative pressure that would kill you instantly.
0:30So, how do trees actually work?
0:33Let’s go back…to the beginning.
0:36The Ancient Battle for the Sky
0:39For over a billion years the ancestors
0:41of plants only inhabited the sun
drenched surfaces of the oceans.
0:45Their bodies were thin and delicate
and absorbed water straight through
0:49their surfaces, getting their
energy through photosynthesis.
0:52Forging sunlight, carbon
dioxide and water into sugar.
0:56But about 470 million years ago they decided
to conquer a hostile alien planet: the land.
1:03Like green rugs with ambition these
plant ancestors began clinging to
1:08the ground wherever it was wet and damp.
1:10But now, with solid ground beneath
and no ability to float around a new
1:14dimension became a place of intense warfare: up.
1:19The higher they grew, the more sun they would
get, while starving their competition below.
1:24Height became a deadly weapon.
The battle for the sky had begun.
1:29Until now, plants were built mostly from
cellulose, which was great for shape,
1:34but not for strength, which
limited how tall they could grow.
1:37Over dozens of millions of
years of evolutionary warfare,
1:40a group of plants developed one of
life's greatest breakthroughs: lignin.
1:44Lignin is a macromolecule made
of ring-shaped structures.
1:48It is rigid, tough, waterproof,
and incredibly hard to break down.
1:52Concrete in a world made of jelly.
1:54It filled gaps between cellulose threads,
stiffening and locking everything into place.
1:59Lignin gave plants the strength to grow
taller and claim the sun for themselves.
2:04But of course now they were
competing with each other,
2:06which must have been really annoying for them.
2:09So as more millions of years passed,
some plants just went all in on lignin
2:13and produced more and more of it,
becoming stiffer, harder and stronger.
2:18Until one day, around 385 million years ago they
2:22got the biological equivalent of
steel reinforced concrete: wood.
2:27More on it later, but with this magic
material the first trees emerged.
2:32Almost immediately they became
the largest living beings alive,
2:35shooting up to 20 meters high into the
sky – and they only got bigger from here.
2:40But this enormous size created
extremely hard problems:
2:45How do you get water from the ground up to the
green parts that do the actual photosynthesis?
2:49And how do you get the sugar they produce
down to the cells that keep you up there?
2:54On the scale of a cell a distance of
a few meters is like you’re working
2:58in Britain while your lunch box is
in Egypt and your drink in New York.
3:05So trees came up with one of the
most amazing ways any organism grows,
3:09and became nearly immortal by accident.
3:13A Conveyor Belt of Death
3:15Let us slice an ancient tree in half
and get to the heart running it all:
3:19the cambium, a razor-thin, circular
zone, just a few stem cells wide.
3:25These stem cells grow inward and outwards,
turning into two groups of specialists.
3:30The inward specialists are on a
conveyor belt of death, the xylem.
3:34With each new division it is
pushing the cambium outwards,
3:37making the tree thicker the older it gets.
3:40As the xylem cells mature their
lignin production goes into overdrive,
3:44and they become hard and stuffy, like
a muscle slowly transforming into bone.
3:49They begin to hollow themselves out, shedding
everything that once made them alive.
3:54What’s left is a corpse, a hard, empty tube.
3:58As the tree grows year after year, new
corpses are layered on old corpses,
4:03forming rings of hardened, dead tissue.
4:06A graveyard of trillions of plant bones.
4:09This is what we call wood.
4:11Stacked together they form a giant network of
pipes that stretches the whole length of the tree.
4:17This network uses the chemical properties of water
4:20and a few other tricks to move
it with incredible efficiency.
4:24Water molecules are, for a lack of a
better word, sticky, like tiny magnets,
4:28and naturally cling tightly to each other.
4:31When one moves, it pulls the next
along with it, like pulling on a rope.
4:35In trees this rope starts in the roots and ends in
the leaves that bathe in the warmth from the sun.
4:41Here the heat from the sun evaporates 95% of
4:45the water that got sucked into the
roots, from billions of tiny pores,
4:48releasing a constant invisible mist of water
molecules around the crown of the tree.
4:53This process, called transpiration in plants,
creates tension on the rope of water molecules,
4:59stretching and lifting the entire column upwards,
all the way from the roots to the leaves.
5:04This pull is so insanely strong that
it can lift water over 100 meters,
5:09which requires sucking forces
equivalent to the pressure of
5:12dozens of atmospheres – as much as the crushing
pressure hundreds of meters deep in the ocean.
5:18Nothing humans have ever built
comes even close to this power.
5:22Even our best machines can’t pull
water higher than about 10 meters,
5:26because the negative pressure required
to pull hard enough makes it boil.
5:30But the water pipes of trees are so tiny
and narrow, almost perfectly airtight that
5:35despite the insane suction pressure inside a
tree, water stays liquid and reaches the top.
5:41As the tree ages old xylem cells
eventually stop working and fill
5:46up with resins and other protective substances.
5:49Slowly they turn into heartwood, a dense,
5:52chemically fortified core that
is extremely resistant to decay.
5:57The core of a mighty tree.
6:00But water is only one half of the story.
6:02The sugar produced in the sky needs to be
transported to nourish cells down below.
6:07And cells from the roots to
the leaves need to coordinate
6:10and exchange information about damage and growth.
6:13This is the job of the cambium stem
cells that grow outwards: the phloem.
6:19The Tiny Living Part of the Tree
6:22As the Cells of the phloem
grow outwards they separate
6:25into three teams and make a brutal compromise.
6:29The first group are Sieve cells and their grim
fate is to become a living transport system.
6:35Although “living” is not exactly right.
6:38As they mature they start to destroy themselves,
6:41digest their organelles and even their
nuclei that houses their genetic code.
6:46At the same time they hollow themselves out,
6:48connecting to the sieve
cells above and below them.
6:51This goes on until they are a
sad shadow of living beings.
6:55A drooling, living tool without a brain
or arms, unable to support themselves.
7:00Only the second group, their
companion cells, keeps them alive.
7:05They connect with the crippled Sieve cells
via tiny channels and start maintaining them.
7:10Sending over energy, instructions
or repairing them if needed.
7:14Running along the entire tree, these
two teams form a tiny and very thin
7:19layer of living sugar pipelines and signal
cables that stretch throughout the entire body.
7:25Providing food and information
wherever it is needed in the tree.
7:29The third team are Parenchyma cells, the silent
7:31workers of the tree that are carrying
out essential labor in the background.
7:35Some are like mini pantries that store nutrients,
7:38sugars or water that the tree uses to survive
the winter, when it is unable to produce food.
7:43Others are like mini healers that can
repair damage, while some go onto the
7:47offensive and create toxins and anti
fungal bio weapons to kill intruders.
7:52On top of the phloem sits
another layer of stem cells.
7:56They are producing a second conveyor
belt of death, moving outside.
8:00Special cells grow from this layer and as they
mature, just like the xylem cells in the center,
8:05they kill themselves for the team,
turning into a hard guard wall – the bark.
8:10Just like your skin, it protects the tiny living
layer from damage, parasites and invaders.
8:19The living part of the stem is really
just this extremely thin and tiny layer,
8:24a few millimeters thick, sitting on
a thick mountain of cell corpses,
8:28surrounded by another layer of cell corpses.
8:31The vast majority of the
biomass of a tree is dead.
8:35This is also why you really should not
damage the bark of trees because while
8:38it seems you are only doing a little damage, you
are actually killing the living part of the tree.
8:44But unless a tree is stopped by droughts,
diseases, storms or a human axe,
8:49this system of being mostly dead kind
of makes trees potentially immortal.
8:54They don’t age like we do, in principle
they could grow this way nearly forever.
8:58Which is why we still have trees
around that were born when the
9:01Egyptians started building their
first pyramid, 5000 years ago.
9:06Really what kills a tree is the world around it.
9:09Trees are not a real biological category but one
of the most successful ideas life has ever had,
9:15and many different species developed on their own.
9:18These plants won the battle for the sky,
solved every challenge that had kept
9:22plants small and fragile and they took
over the planet in a few million years.
9:28Even today three trillion of
them cast their majestic shadows.
9:33But we’ve barely covered half of it:
on top and below there are the crown
9:36and the root system – one building
the tree from air, another mining
9:40minerals with acid and involved in complex
communications with fungi and other trees.
9:46There’s so much more to talk about, so we’re
already working on the next part - stay tuned!
9:53Trees are truly incredible – but many
of our most beautiful forests are
9:56disappearing fast and we’re running
out of time to protect what’s left.
10:00That’s why we have partnered up with Planet Wild.
10:03Planet Wild is a community-based
nature protection organization
10:07that supports conservation
projects around the globe.
10:10Every month, their community of over 15,000
members funds a new mission to restore nature.
10:16We at kurzgesagt really value transparency.
10:19That’s why we love that Planet Wild
documents all their missions in video
10:23reports right here on YouTube so you can
see what your contribution helped achieve.
10:28Take their underground forest mission in Tanzania:
10:32While you think this desert is dead,
there’s actually life still here.
10:36Beneath the surface, underground
forests are just waiting to grow.
10:40And with an ancient technique,
Planet Wild helped make that happen.
10:43If you would like to help our planet’s
ecosystems, consider joining Planet Wild.
10:48You can give any amount that feels
right to you – every dollar counts.
10:52The first 100 people to sign up using our code
10:54KURZGESAGT11 will get their
first month paid for by us!
10:58Just scan the QR code or click
the link in the description.
11:02Make a tree friend, and join the
Planet Wild community – today.
11:06If you want to see them in action first, check
out their underground forest mission here.
11:12It’s here – the 10 year anniversary
edition of our Human Era Calendar!
11:16A decade ago we created a calendar
to reframe time itself. By adding
11:2110,000 years to our timeline we
include all of human history.
11:26This edition is better than ever:
12 vibrant kurzgesagt illustrations
11:30tell the story of humanity’s special
connection with the stars – from the
11:34first creature to look up at the night
sky to our future among the stars.
11:38It’s a year’s worth of art for your home,
11:40with plenty of space to plan your days
or record your adventures in 12,026.
11:46Join the thousands of birbs who get the
calendar every year and keep this channel going.
11:51To celebrate 10 years, we’ve prepared
some very special deals for you.
11:56You can now also pre-order the very
first kurzgesagt artbook – a vibrant,
12:00jam-packed collection of every calendar
12:03illustration we’ve ever made.
And to commemorate that trees
12:06are some of the most extreme beings on
earth, we created this video poster.
12:10It’s available on the shop now.
12:12Thank you so much for
supporting real, human-made art!
