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00:00:02,133 --> 00:00:04,166
NARRATOR:
A young world.

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The atmosphere toxic.

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00:00:08,633 --> 00:00:13,333
The land barren and forbidding.

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00:00:14,600 --> 00:00:19,366
Until the arrival of a life form
that changed everything.

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Plants.

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DORI CONTRERAS:
Everything about the landscape

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was influenced by plants
moving onto the land.

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NARRATOR:
Evolving in the oceans,

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00:00:32,600 --> 00:00:35,033
they eventually partner
with fungi

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00:00:35,033 --> 00:00:37,500
to turn an alien world...

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One of the most bizarre
prehistoric landscapes of all.

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NARRATOR:
...into one we recognize today.

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00:00:44,500 --> 00:00:46,166
(eruption roars)

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00:00:46,166 --> 00:00:49,466
Along the way, they're subjected
to cataclysm after cataclysm...

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00:00:51,433 --> 00:00:55,500
LYNN SOREGHAN:
Ice could have covered
the entire planet.

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NARRATOR:
...and alter
the very Earth itself.

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CHRISTOPHER JACKSON:
This interplay between biology

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00:01:02,233 --> 00:01:05,233
and geology has utterly
transformed our land.

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00:01:05,233 --> 00:01:09,000
NARRATOR:
How did an inhospitable
rocky planet...

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...become an oasis for life?

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"Ancient Earth: Life Rising."

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00:01:17,900 --> 00:01:20,733
Right now, on "NOVA."

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♪ ♪

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♪ ♪

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NARRATOR:
Viewed from above, planet
Earth is a riot of colors.

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But there is one color
that is special.

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One that reminds us our home is
a living, breathing planet,

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unique in our solar system.

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♪ ♪

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Green.

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(wind howling)

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This is the story
of how Earth transformed...

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♪ ♪

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...from a hostile
and inhospitable world...

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...into a haven of opportunity
for life.

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00:02:51,400 --> 00:02:53,100
Our green planet
wasn't preordained.

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It's the result of an immense
struggle over millions of years.

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NARRATOR:
How plant life rose from
the oceans

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to dominate a rugged
and desolate landscape.

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ALY BAUMGARTNER:
Everything that you know
about the planet,

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everything that you think
of when you look outside,

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is because of plants.

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00:03:16,266 --> 00:03:19,466
NARRATOR:
And how plants reshaped
Earth itself.

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CONTRERAS:
Without plants,

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Earth would be nothing like
it is today.

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JACKSON:
Plants are literal
terra-formers.

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They transformed bare rock
into life-giving soil.

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♪ ♪

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00:03:31,466 --> 00:03:35,433
KIRK JOHNSON:
Plants are elaborate,
beautiful little machines.

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These are the most
amazing things in the world.

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00:03:44,100 --> 00:03:45,666
("Never Close Enough"
by SIPHO. playing)

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♪ Oh, we won't ever hear
the silence ♪

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♪ Or ever see the colors ♪

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00:03:52,066 --> 00:03:53,366
(exploding)

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00:03:53,366 --> 00:03:55,700
♪ That never lived in
our minds ♪

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00:03:55,700 --> 00:04:00,100
♪ ♪

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♪ Just a moment ♪

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00:04:02,166 --> 00:04:04,733
♪ Never too far out ♪

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00:04:04,733 --> 00:04:06,933
♪ Never close enough ♪

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♪ ♪

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NARRATOR:
Half a billion years after
Earth was formed...

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...the planet is
covered by an endless ocean...

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...broken up only by a few
remote volcanic islands,

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00:04:52,233 --> 00:04:56,100
with no trace of life
on the surface.

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00:04:58,800 --> 00:05:02,433
But this is a living world.

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00:05:07,433 --> 00:05:11,600
To find ancestors of modern
life, many scientists believe

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you would have to leave
the surface behind...

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♪ ♪

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00:05:18,733 --> 00:05:22,000
...and travel
to the depths of the oceans.

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It's thought early life thrived
in superheated geothermal vents.

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♪ ♪

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These single-celled organisms
would've been

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uniquely adapted to life
in this harsh environment,

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and would ultimately give rise
to plants

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and everything
that will ever live on Earth.

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♪ ♪

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But for now,
they're stuck in the ocean,

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because large landmasses...

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00:06:07,900 --> 00:06:09,900
(eruption roaring,
water hissing)

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...do not yet exist.

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00:06:17,266 --> 00:06:19,366
So there's a theory that four
billion years ago,

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the only land on Earth were just

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a few black volcanic islands

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scattered in the ocean.

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♪ ♪

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This early land was made
of basalt,

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which is cooled lava.

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And it contains magnesium,
calcium--

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things that life requires.

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AISHA MORRIS:
The problem was that
these small early

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volcanic islands were
short-lived,

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because they were smashed to
pieces by the tides

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created by the much closer moon
at that time.

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NARRATOR:
For dry land to form
and persist,

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one of the world's
most powerful geologic forces

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had to begin:

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00:07:01,100 --> 00:07:04,100
plate tectonics.

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00:07:04,100 --> 00:07:06,633
(eruption roars)

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MORRIS:
Plate tectonics really
tries to explain

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00:07:11,166 --> 00:07:13,666
the land forms that we see
on Earth:

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00:07:13,666 --> 00:07:16,066
things like volcanoes,
events such as earthquakes.

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00:07:18,233 --> 00:07:20,833
And it's really based
on the idea that plates

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00:07:20,833 --> 00:07:23,233
on the surface of the Earth
move around in relation

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00:07:23,233 --> 00:07:26,133
to one another, and sometimes
go beneath each other,

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00:07:26,133 --> 00:07:27,800
sometimes crash into each other,

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and sometimes slide past
each other.

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NARRATOR:
This geologic process
would prove

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00:07:34,000 --> 00:07:39,500
to be the key that would change
the surface forever.

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♪ ♪

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But its beginnings
are shrouded in mystery.

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HAZEN:
The beginnings of plate
tectonics is so controversial.

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Some people think it was

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00:07:53,933 --> 00:07:56,766
density differences and crust
being pulled down by gravity.

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00:07:59,433 --> 00:08:05,433
NARRATOR:
But some incredible new
evidence has been discovered

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00:08:05,433 --> 00:08:10,733
that suggests
an extra-terrestrial origin.

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00:08:10,733 --> 00:08:13,133
Sometimes geology gives us
great clues

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about how early processes
occurred.

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NARRATOR:
Scientists have found
microscopic structures

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called spherules,
thought to be formed

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00:08:24,333 --> 00:08:26,400
by asteroid impacts

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00:08:26,400 --> 00:08:31,166
3.2 billion years ago,
hidden in ancient rocks.

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These are located
alongside rocks

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00:08:34,333 --> 00:08:38,433
that show indications
of plate tectonics.

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00:08:38,433 --> 00:08:40,300
So it's really hard
to know for sure,

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00:08:40,300 --> 00:08:42,266
because this happened
so long ago,

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00:08:42,266 --> 00:08:44,066
but one of the things that
may have happened

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is that these impacts

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00:08:45,400 --> 00:08:47,900
may have actually
started the magma moving.

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00:08:50,066 --> 00:08:52,533
These asteroid impacts
would've ruptured the crust.

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00:08:52,533 --> 00:08:55,700
They may have played
some role in starting the plates

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00:08:55,700 --> 00:08:58,966
moving and allowing plates
to sink.

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00:08:58,966 --> 00:09:02,100
This may have
started plate tectonics.

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00:09:06,200 --> 00:09:11,466
♪ ♪

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00:09:16,166 --> 00:09:19,700
NARRATOR:
Data suggest that one of these
giant asteroids

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00:09:19,700 --> 00:09:22,533
is as much as 30 miles across.

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00:09:22,533 --> 00:09:27,233
♪ ♪

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00:09:29,333 --> 00:09:31,900
More than three times the size
of the one

138
00:09:31,900 --> 00:09:35,200
believed to have
wiped out the dinosaurs.

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00:09:35,200 --> 00:09:42,033
♪ ♪

140
00:09:42,033 --> 00:09:45,500
(explosion roars)

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00:09:48,666 --> 00:09:53,466
Early life forms in its path
would be lost to oblivion.

142
00:09:58,133 --> 00:10:00,033
But somehow,

143
00:10:00,033 --> 00:10:03,533
in its deep ocean hideaway,

144
00:10:03,533 --> 00:10:07,033
some early life clings on,

145
00:10:07,033 --> 00:10:13,566
and its odds for making it onto
land have just gotten better.

146
00:10:15,033 --> 00:10:17,433
Because with
the advent of plate tectonics

147
00:10:17,433 --> 00:10:19,900
comes an entirely
new kind of rock...

148
00:10:22,300 --> 00:10:25,833
...that could
allow life to get a foothold.

149
00:10:28,833 --> 00:10:34,300
This rock forms during
a process called subduction.

150
00:10:34,300 --> 00:10:36,600
Subduction is when one slab of
rock,

151
00:10:36,600 --> 00:10:38,500
a tectonic plate, is forced down

152
00:10:38,500 --> 00:10:39,900
beneath another tectonic plate.

153
00:10:43,200 --> 00:10:44,633
EDMONDS:
The subducting plate brings
water down

154
00:10:44,633 --> 00:10:46,400
into the interior
of the Earth, and that water

155
00:10:46,400 --> 00:10:49,366
is a bit like adding salt
to an icy road.

156
00:10:49,366 --> 00:10:53,300
So adding water to hot rock
makes it melt,

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00:10:53,300 --> 00:10:55,200
but this melt is really special.

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00:10:55,200 --> 00:10:57,133
It's really rich
in silica and oxygen,

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00:10:57,133 --> 00:10:59,433
and when it rises
to the surface,

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it forms granite.

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00:11:03,400 --> 00:11:07,266
NARRATOR:
A rock that shapes the surface
of Earth as we know it today.

162
00:11:09,333 --> 00:11:12,333
Now, you may think of granite
as just a speckled

163
00:11:12,333 --> 00:11:15,566
gray rock, but it actually
has a really special property

164
00:11:15,566 --> 00:11:18,233
that make it a wonderful
land-building material.

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00:11:21,100 --> 00:11:23,100
NARRATOR:
Granite has a low density.

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00:11:23,100 --> 00:11:24,533
HAZEN:
So we all understand density

167
00:11:24,533 --> 00:11:27,000
because we put ice cubes
in our drink,

168
00:11:27,000 --> 00:11:29,666
and when we do,
about ten percent of that ice

169
00:11:29,666 --> 00:11:31,400
sticks above the water,

170
00:11:31,400 --> 00:11:34,066
'cause ice is ten percent
less dense than water.

171
00:11:34,066 --> 00:11:36,200
And in the exact same way,

172
00:11:36,200 --> 00:11:39,133
granite is about ten percent
less dense than basalt,

173
00:11:39,133 --> 00:11:41,233
so ten percent of the granite

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00:11:41,233 --> 00:11:43,700
sticks up above basalt.

175
00:11:43,700 --> 00:11:45,933
♪ ♪

176
00:11:45,933 --> 00:11:47,600
This means that after
granite's formed,

177
00:11:47,600 --> 00:11:49,200
this hard, heavy rock

178
00:11:49,200 --> 00:11:51,066
actually floats on top

179
00:11:51,066 --> 00:11:54,100
of the partially molten basalt
beneath it.

180
00:11:59,066 --> 00:12:02,266
(wind howling)

181
00:12:02,266 --> 00:12:07,333
♪ ♪

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00:12:07,333 --> 00:12:11,700
NARRATOR:
As plate tectonics continue,
over billions of years,

183
00:12:11,700 --> 00:12:14,133
vast swathes of rock

184
00:12:14,133 --> 00:12:17,600
gradually emerge
across the planet.

185
00:12:22,966 --> 00:12:26,266
Earth's first landmasses
are born.

186
00:12:45,533 --> 00:12:47,333
A couple of billion years

187
00:12:47,333 --> 00:12:50,266
after the inception of
plate tectonics...

188
00:12:52,133 --> 00:12:55,333
...a multitude of
continental-scale landmasses

189
00:12:55,333 --> 00:12:58,900
are strewn across
the surface of the planet.

190
00:13:04,600 --> 00:13:07,333
A vast frontier.

191
00:13:11,233 --> 00:13:15,266
A rocky world with plenty
of minerals

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00:13:15,266 --> 00:13:19,166
containing nutrients like
potassium and phosphorus,

193
00:13:19,166 --> 00:13:22,233
key elements for life.

194
00:13:25,500 --> 00:13:30,300
♪ ♪

195
00:13:32,633 --> 00:13:36,533
For any organism that can adapt
to this new territory,

196
00:13:36,533 --> 00:13:39,666
incredible opportunities await.

197
00:13:42,200 --> 00:13:47,233
♪ ♪

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00:13:58,366 --> 00:14:00,900
Dwelling in the shallows,

199
00:14:00,900 --> 00:14:04,000
within touching
distance of the land...

200
00:14:06,633 --> 00:14:10,100
...are recognizable,
plant-like life.

201
00:14:12,166 --> 00:14:16,133
Marine algae.

202
00:14:17,500 --> 00:14:19,133
Descendants of the early life

203
00:14:19,133 --> 00:14:22,033
that originated
in geothermal vents.

204
00:14:25,833 --> 00:14:29,133
They bask in
the light-filled shallows,

205
00:14:29,133 --> 00:14:31,333
having adopted
an absolutely incredible way

206
00:14:31,333 --> 00:14:35,166
to harvest energy
directly from the sun:

207
00:14:35,166 --> 00:14:39,066
photosynthesis.

208
00:14:39,066 --> 00:14:41,233
Photosynthesis is a chemical
reaction

209
00:14:41,233 --> 00:14:43,333
by which plants take light from
the sun

210
00:14:43,333 --> 00:14:46,700
and combine it with water and
carbon dioxide

211
00:14:46,700 --> 00:14:50,200
to make oxygen and glucose,
the sugar they use for energy.

212
00:14:51,966 --> 00:14:54,200
NARRATOR:
Marine algae have evolved to use

213
00:14:54,200 --> 00:14:59,066
a crucial cellular
innovation called chloroplasts,

214
00:14:59,066 --> 00:15:02,400
specialized structures
filled with chlorophyll,

215
00:15:02,400 --> 00:15:05,800
a compound that helps
harness the sun's energy

216
00:15:05,800 --> 00:15:10,500
and gives them
their distinctive green hue.

217
00:15:13,666 --> 00:15:16,500
But they are still confined
to the water.

218
00:15:18,700 --> 00:15:21,866
An environment which they
are perfectly adapted to.

219
00:15:23,466 --> 00:15:25,333
A watery environment is lovely

220
00:15:25,333 --> 00:15:26,466
if you're a plant.

221
00:15:26,466 --> 00:15:28,833
It's like being surrounded

222
00:15:28,833 --> 00:15:31,100
by a bath of your food.

223
00:15:31,100 --> 00:15:32,533
You've got nutrients available
to you,

224
00:15:32,533 --> 00:15:34,200
there's no danger of drying out,

225
00:15:34,200 --> 00:15:38,733
and you don't have to worry
about gravity or soil.

226
00:15:40,600 --> 00:15:42,833
NARRATOR:
Migrating onto land
at this point

227
00:15:42,833 --> 00:15:47,066
would require
a huge evolutionary leap.

228
00:15:47,066 --> 00:15:49,266
For plants to live outside of
water,

229
00:15:49,266 --> 00:15:51,266
it's a bit like me trying to
live on Mars

230
00:15:51,266 --> 00:15:53,066
without a space suit.

231
00:15:55,766 --> 00:15:59,266
NARRATOR:
But while marine algae can't
quite make it from the ocean

232
00:15:59,266 --> 00:16:00,833
onto dry land,

233
00:16:00,833 --> 00:16:05,833
they can adapt to another,
more accessible environment:

234
00:16:05,833 --> 00:16:08,733
fresh water.

235
00:16:10,866 --> 00:16:13,800
Eventually,
the algae take up residence

236
00:16:13,800 --> 00:16:16,666
in the lakes,
streams, and rivers.

237
00:16:19,266 --> 00:16:23,066
From there, around
half a billion years ago...

238
00:16:25,033 --> 00:16:29,166
...the algae begin their
slow journey onto the land.

239
00:16:31,266 --> 00:16:33,700
We may never know
the combination of factors

240
00:16:33,700 --> 00:16:36,766
that spurred
green algae on land.

241
00:16:36,766 --> 00:16:39,566
NARRATOR:
Maybe it was the changing of
Earth's landscapes

242
00:16:39,566 --> 00:16:41,666
to more clement conditions,

243
00:16:41,666 --> 00:16:45,800
or the time needed
for profound genetic change.

244
00:16:45,800 --> 00:16:50,900
But whatever the reason, green
algae begins to come ashore.

245
00:16:53,300 --> 00:16:55,633
The journey is likely
to have started

246
00:16:55,633 --> 00:17:00,900
at the pebbly shorelines
of freshwater lakes and rivers.

247
00:17:00,900 --> 00:17:05,666
Some eventually evolve
a thick waxy coating

248
00:17:05,666 --> 00:17:09,966
that stops them from drying out
in their harsh new environment.

249
00:17:11,566 --> 00:17:16,566
But this effective adaptation
is a double-edged sword...

250
00:17:19,766 --> 00:17:22,133
...making it more
difficult to absorb nutrients

251
00:17:22,133 --> 00:17:25,333
from their surroundings,
like they did in the water,

252
00:17:25,333 --> 00:17:30,533
and making success
on land nearly impossible.

253
00:17:36,433 --> 00:17:41,500
So, how did plants come
to thrive on land?

254
00:17:41,500 --> 00:17:47,100
♪ ♪

255
00:17:58,266 --> 00:18:00,733
Though this may look like an
ordinary field,

256
00:18:00,733 --> 00:18:05,466
it contains one of the world's
most important geological sites,

257
00:18:05,466 --> 00:18:08,733
and the secret to what
helped plants survive on land.

258
00:18:11,100 --> 00:18:12,900
This is an incredibly exciting
place for me to be,

259
00:18:12,900 --> 00:18:15,400
because more than a hundred
years ago, this site

260
00:18:15,400 --> 00:18:17,433
where we are today
was excavated to reveal

261
00:18:17,433 --> 00:18:21,466
the most incredible set of 400-
million-year-old plant fossils.

262
00:18:25,566 --> 00:18:28,100
What's special about the fossils
from this particular site was,

263
00:18:28,100 --> 00:18:29,633
the degree of preservation

264
00:18:29,633 --> 00:18:34,033
of the plant material meant
that we got some amazing clues

265
00:18:34,033 --> 00:18:37,333
as to how they actually made
landfall in the first place.

266
00:18:37,333 --> 00:18:41,366
♪ ♪

267
00:18:41,366 --> 00:18:44,000
NARRATOR:
Around 400 million years ago,

268
00:18:44,000 --> 00:18:45,766
this area looked completely
different

269
00:18:45,766 --> 00:18:47,333
from how it looks today.

270
00:18:47,333 --> 00:18:52,266
It resembled
Yellowstone National Park,

271
00:18:52,266 --> 00:18:54,000
where boiling mineralized waters

272
00:18:54,000 --> 00:18:56,766
cascade down rocky terraces.

273
00:18:59,166 --> 00:19:02,100
FIELD:
So the ancient hot springs
that were here at Rhynie

274
00:19:02,100 --> 00:19:05,366
turned any plant material
that they touched into rock,

275
00:19:05,366 --> 00:19:07,066
and that got buried
over millions of years.

276
00:19:07,066 --> 00:19:11,066
The resulting bed of fossils is
what we call the Rhynie Chert.

277
00:19:11,066 --> 00:19:17,266
♪ ♪

278
00:19:17,266 --> 00:19:19,833
This fossil is really amazing.

279
00:19:19,833 --> 00:19:22,800
If you look closely,
you can see these circles

280
00:19:22,800 --> 00:19:24,800
in the surface of the fossil.

281
00:19:27,266 --> 00:19:30,266
And those circles
are actually cross sections

282
00:19:30,266 --> 00:19:32,000
through the stems of
ancient plants

283
00:19:32,000 --> 00:19:34,066
that grew all around here.

284
00:19:35,766 --> 00:19:37,466
NARRATOR:
And you can see
something unusual

285
00:19:37,466 --> 00:19:40,600
when you look at them
under a microscope.

286
00:19:40,600 --> 00:19:42,666
What we see is,
there's this light banding

287
00:19:42,666 --> 00:19:46,066
around the top,
and that's plant tissue,

288
00:19:46,066 --> 00:19:48,133
but if you look even more
closely,

289
00:19:48,133 --> 00:19:50,633
you see these dark brown
thread-like structures

290
00:19:50,633 --> 00:19:52,166
weaving between the cells

291
00:19:52,166 --> 00:19:54,300
and actually invading
some of the plant cells.

292
00:19:54,300 --> 00:19:57,800
And those thread-like
structures are actually fungi.

293
00:19:59,800 --> 00:20:02,066
NARRATOR:
This incredible evidence shows

294
00:20:02,066 --> 00:20:04,766
that plants actually
teamed up with another

295
00:20:04,766 --> 00:20:08,900
kind of life form
to help get onto the land--

296
00:20:08,900 --> 00:20:10,500
fungi.

297
00:20:14,200 --> 00:20:16,266
Rhynie Chert fossils are
some of the only

298
00:20:16,266 --> 00:20:18,666
fossils on Earth where you can
see this ancient link

299
00:20:18,666 --> 00:20:20,433
between plants and fungi.

300
00:20:25,400 --> 00:20:28,233
♪ ♪

301
00:20:28,233 --> 00:20:30,333
NARRATOR:
Fungi, however,
were not newcomers

302
00:20:30,333 --> 00:20:32,433
to the land surfaces.

303
00:20:34,933 --> 00:20:37,000
Fungi made its way onto
terrestrial land

304
00:20:37,000 --> 00:20:38,600
probably hundreds of millions of
years

305
00:20:38,600 --> 00:20:39,733
before plants.

306
00:20:41,833 --> 00:20:44,200
 
NARRATOR:
They were able to live
on the land

307
00:20:44,200 --> 00:20:46,200
consuming bacteria
and drawing minerals

308
00:20:46,200 --> 00:20:49,200
directly from the rocks below.

309
00:20:51,600 --> 00:20:54,000
FIELD:
So fungi are able to get hold
of these nutrients

310
00:20:54,000 --> 00:20:58,600
by exuding organic acids
out of their fungal hyphae,

311
00:20:58,600 --> 00:20:59,766
which are thread-like filaments

312
00:20:59,766 --> 00:21:01,566
that form
the majority of the fungus.

313
00:21:06,700 --> 00:21:08,833
NARRATOR:
Even though the Rhynie Chert
fossils

314
00:21:08,833 --> 00:21:12,633
are around
400 million years old,

315
00:21:12,633 --> 00:21:14,700
this union of plants and fungi

316
00:21:14,700 --> 00:21:17,900
must have occurred
millions of years earlier.

317
00:21:19,633 --> 00:21:21,700
CONTRERAS:
Plants benefited
from the partnership

318
00:21:21,700 --> 00:21:23,900
because they got the nutrients
from the rock's surface

319
00:21:23,900 --> 00:21:25,400
that were broken down

320
00:21:25,400 --> 00:21:26,833
by the fungi.

321
00:21:26,833 --> 00:21:28,333
And then the fungi
benefited because

322
00:21:28,333 --> 00:21:30,233
they got to use the sugars
that were supplied

323
00:21:30,233 --> 00:21:32,966
from the plants
doing photosynthesis.

324
00:21:34,166 --> 00:21:37,900
NARRATOR:
Bolstered by this
new relationship with fungi,

325
00:21:37,900 --> 00:21:40,733
plants evolved
the ability to exchange sugars

326
00:21:40,733 --> 00:21:44,500
for vital nutrients
like nitrogen and phosphorus.

327
00:21:47,300 --> 00:21:50,100
Even with their thick,
water-retentive coating,

328
00:21:50,100 --> 00:21:53,133
they can still get all
the nutrients they need.

329
00:21:54,966 --> 00:21:58,000
The emergence of this newly
evolved mutual relationship,

330
00:21:58,000 --> 00:21:59,466
or symbiosis,

331
00:21:59,466 --> 00:22:04,266
is a key turning point
for plants' journey.

332
00:22:04,266 --> 00:22:11,766
Now plants can finally survive
out of the water on the land.

333
00:22:11,766 --> 00:22:14,366
The symbiosis between land
plants and fungi

334
00:22:14,366 --> 00:22:16,566
is super-important.

335
00:22:16,566 --> 00:22:19,833
It's essential
for how ecosystems evolved

336
00:22:19,833 --> 00:22:21,966
and how they work today.

337
00:22:24,200 --> 00:22:26,533
BAUMGARTNER:
After millions of years

338
00:22:26,533 --> 00:22:28,600
and lots of evolutionary tries,

339
00:22:28,600 --> 00:22:32,033
plants were
finally onto the land.

340
00:22:38,666 --> 00:22:42,933
♪ ♪

341
00:22:42,933 --> 00:22:46,133
NARRATOR:
Plants and fungi created
one of Earth's

342
00:22:46,133 --> 00:22:49,400
first complex
terrestrial ecosystems.

343
00:22:49,400 --> 00:22:55,400
♪ ♪

344
00:22:55,400 --> 00:23:00,766
And their partnership
continues to this day.

345
00:23:00,766 --> 00:23:05,500
♪ ♪

346
00:23:05,500 --> 00:23:08,233
It's often easy to
spot mushrooms,

347
00:23:08,233 --> 00:23:12,233
which are the reproductive
part of some types of fungi.

348
00:23:15,133 --> 00:23:19,933
But most fungi live underground,
where we can't see them.

349
00:23:19,933 --> 00:23:21,800
So this plant has grown

350
00:23:21,800 --> 00:23:23,833
with a fungal partner,
and you can see that,

351
00:23:23,833 --> 00:23:25,800
with the plant roots being
intermingled

352
00:23:25,800 --> 00:23:27,100
with fungal filaments,

353
00:23:27,100 --> 00:23:29,833
and these wrap themselves
around the plant roots

354
00:23:29,833 --> 00:23:32,666
and form these
intimate associations.

355
00:23:40,000 --> 00:23:42,200
NARRATOR:
These associations are so vital

356
00:23:42,200 --> 00:23:46,966
that nearly 90% of plants living
today are dependent on them.

357
00:23:46,966 --> 00:23:50,300
FIELD:
It's really easy
to overlook fungi because,

358
00:23:50,300 --> 00:23:52,866
for the most part,
they live underground,

359
00:23:52,866 --> 00:23:55,333
whilst plants grow much taller
and are more obvious.

360
00:23:58,033 --> 00:24:00,233
NARRATOR:
But some fossil evidence

361
00:24:00,233 --> 00:24:02,733
from around
420 million years ago

362
00:24:02,733 --> 00:24:06,900
suggests that this balance
once looked quite different.

363
00:24:14,366 --> 00:24:19,400
♪ ♪

364
00:24:28,500 --> 00:24:32,700
Something utterly astonishing
has happened to some fungi.

365
00:24:35,433 --> 00:24:37,933
They have become giants.

366
00:24:40,133 --> 00:24:42,666
♪ ♪

367
00:24:42,666 --> 00:24:46,766
Colossal fungal spikes tower
over the landscape.

368
00:24:48,433 --> 00:24:51,733
They're called Prototaxites.

369
00:24:56,600 --> 00:24:59,266
Standing over 20 feet high,

370
00:24:59,266 --> 00:25:01,633
they reproduce
by releasing spores

371
00:25:01,633 --> 00:25:06,333
that are carried by the wind.

372
00:25:06,333 --> 00:25:10,300
CONTRERAS:
The Prototaxites landscape
would've been an alien world.

373
00:25:12,733 --> 00:25:14,600
NARRATOR:
So alien

374
00:25:14,600 --> 00:25:19,366
that when the fossils were
first discovered back in 1843,

375
00:25:19,366 --> 00:25:22,800
scientists were not
even sure what they were.

376
00:25:25,166 --> 00:25:26,900
It was a very strange

377
00:25:26,900 --> 00:25:28,533
and odd thing when people
found it.

378
00:25:28,533 --> 00:25:31,133
 
It was shaped
like a chunk of wood.

379
00:25:33,100 --> 00:25:36,933
NARRATOR:
But when they took
a much closer look,

380
00:25:36,933 --> 00:25:40,466
they discovered
something incredible.

381
00:25:40,466 --> 00:25:41,666
So what this is

382
00:25:41,666 --> 00:25:43,866
is a very thin slice of
Prototaxites.

383
00:25:45,633 --> 00:25:48,800
♪ ♪

384
00:25:48,800 --> 00:25:51,066
And we find that, unlike a log,

385
00:25:51,066 --> 00:25:53,000
which would be full of
woody cells,

386
00:25:53,000 --> 00:25:55,533
instead we find a mass of these
fungal filaments,

387
00:25:55,533 --> 00:25:59,133
reminiscent of fungi today.

388
00:25:59,133 --> 00:26:00,733
JOHNSON:
It creates,

389
00:26:00,733 --> 00:26:04,300
in my mind, one of the most
bizarre prehistoric landscapes

390
00:26:04,300 --> 00:26:06,166
of all, 'cause there's
nothing like it today.

391
00:26:09,200 --> 00:26:13,466
NARRATOR:
The towering Prototaxites
dominate the landscape.

392
00:26:14,866 --> 00:26:17,766
Plants, by contrast,
are still tiny,

393
00:26:17,766 --> 00:26:21,066
measuring just
a few inches or less.

394
00:26:22,500 --> 00:26:24,433
Stuck by the water's edge,

395
00:26:24,433 --> 00:26:28,000
near to where
they first made landfall.

396
00:26:30,000 --> 00:26:31,833
LYDON:
So, even though plants

397
00:26:31,833 --> 00:26:33,466
have made it out of the water,

398
00:26:33,466 --> 00:26:35,066
they're still confined to
the edges

399
00:26:35,066 --> 00:26:36,933
of lakes and rivers.

400
00:26:36,933 --> 00:26:39,700
A lot of the land surface on
Earth at this time

401
00:26:39,700 --> 00:26:45,266
 
was also quite dry,
and maybe rocky or very sandy.

402
00:26:45,266 --> 00:26:48,800
NARRATOR:
With no way of holding on to
that water inland,

403
00:26:48,800 --> 00:26:53,666
Earth could've remained
a fungal paradise.

404
00:26:53,666 --> 00:26:55,200
For plants to establish
themselves

405
00:26:55,200 --> 00:26:56,700
away from the water,

406
00:26:56,700 --> 00:26:59,366
they were gonna have to change,

407
00:26:59,366 --> 00:27:01,266
to evolve new traits that
allowed them

408
00:27:01,266 --> 00:27:03,566
to live in the new environment.

409
00:27:07,700 --> 00:27:10,766
NARRATOR:
But there is a vital ingredient
missing.

410
00:27:10,766 --> 00:27:14,900
♪ ♪

411
00:27:14,900 --> 00:27:16,933
Something that seems like it has

412
00:27:16,933 --> 00:27:20,033
always been part
of the fabric of Earth.

413
00:27:22,066 --> 00:27:25,866
♪ ♪

414
00:27:25,866 --> 00:27:28,366
Soil.

415
00:27:33,100 --> 00:27:37,433
Just one teaspoon of this
crumbly brown stuff

416
00:27:37,433 --> 00:27:39,666
includes more living organisms

417
00:27:39,666 --> 00:27:41,166
than there are people on the
planet,

418
00:27:41,166 --> 00:27:44,333
and that is absolutely
unbelievable.

419
00:27:45,433 --> 00:27:47,066
Despite the fact that soils

420
00:27:47,066 --> 00:27:49,933
only make up a small portion of
the Earth's surface,

421
00:27:49,933 --> 00:27:51,633
there are thousands
of varieties,

422
00:27:51,633 --> 00:27:53,733
including more than 20,000
in the U.S. alone.

423
00:27:53,733 --> 00:27:59,433
♪ ♪

424
00:27:59,433 --> 00:28:01,466
NARRATOR:
Soil is formed by the combined
action

425
00:28:01,466 --> 00:28:04,133
of organisms
like bacteria and fungi

426
00:28:04,133 --> 00:28:09,566
working on biological matter
like fallen leaves.

427
00:28:09,566 --> 00:28:11,966
Combined with
particles like sand or clay,

428
00:28:11,966 --> 00:28:14,366
it is the
perfect material to hold

429
00:28:14,366 --> 00:28:17,833
all the ingredients
plants need to thrive.

430
00:28:21,033 --> 00:28:23,633
Soil traps and holds on to water
and nutrients

431
00:28:23,633 --> 00:28:26,100
so that plants
can use them all year round.

432
00:28:28,666 --> 00:28:30,500
If we look in the fossil record,

433
00:28:30,500 --> 00:28:33,500
we see something
absolutely remarkable.

434
00:28:33,500 --> 00:28:35,733
About 470 million years ago,

435
00:28:35,733 --> 00:28:38,700
soils as we know them today
did not exist.

436
00:28:39,900 --> 00:28:42,100
Instead, we had the earliest
version of soils,

437
00:28:42,100 --> 00:28:44,100
what we call proto-soils.

438
00:28:44,100 --> 00:28:46,266
They were only
maybe a millimeter thick.

439
00:28:48,466 --> 00:28:50,433
They were formed from
very thin layers

440
00:28:50,433 --> 00:28:52,666
of bacterial or fungal mats;
they just didn't have

441
00:28:52,666 --> 00:28:55,533
the same kind of building
blocks that soils today have.

442
00:28:59,900 --> 00:29:04,500
NARRATOR:
Early fungi do not need soil
to thrive.

443
00:29:06,800 --> 00:29:09,866
But plants need something
to support and nourish them

444
00:29:09,866 --> 00:29:13,700
if they are to survive
farther away from the water.

445
00:29:15,433 --> 00:29:20,366
Soon, they start making soil.

446
00:29:20,366 --> 00:29:25,266
♪ ♪

447
00:29:25,266 --> 00:29:28,566
They begin slowly,

448
00:29:28,566 --> 00:29:31,733
over millions of years,

449
00:29:31,733 --> 00:29:33,700
breaking down the bare rock

450
00:29:33,700 --> 00:29:38,933
with tiny root-like
structures called rhizoids,

451
00:29:38,933 --> 00:29:42,366
mixing in nutrients
from their fungal partners.

452
00:29:43,533 --> 00:29:49,100
♪ ♪

453
00:29:49,100 --> 00:29:52,533
But the true
transformative ingredient...

454
00:29:55,033 --> 00:29:57,900
...is the plants themselves.

455
00:30:04,400 --> 00:30:08,566
Generation after generation
breaks down after death,

456
00:30:08,566 --> 00:30:11,266
building up a bed of soil.

457
00:30:16,100 --> 00:30:21,133
Turning once inert rock
into a living layer.

458
00:30:26,333 --> 00:30:31,366
♪ ♪

459
00:30:42,000 --> 00:30:46,200
Fast-forward 20 million years.

460
00:30:46,200 --> 00:30:47,833
And with the growing
soil layers,

461
00:30:47,833 --> 00:30:49,966
plants are transforming.

462
00:30:49,966 --> 00:30:54,000
♪ ♪

463
00:30:56,800 --> 00:30:58,833
They're much bigger.

464
00:31:00,966 --> 00:31:03,500
And their ability to move water
through their tissues

465
00:31:03,500 --> 00:31:05,700
by a kind of plumbing

466
00:31:05,700 --> 00:31:09,133
has allowed them to live
farther away from the water.

467
00:31:12,166 --> 00:31:15,766
They're now more varied,
with deeper roots

468
00:31:15,766 --> 00:31:18,600
to support their taller stems.

469
00:31:24,633 --> 00:31:27,266
Prototaxites, the giant fungi,

470
00:31:27,266 --> 00:31:29,466
still tower over them.

471
00:31:32,866 --> 00:31:34,700
But soil makes it possible

472
00:31:34,700 --> 00:31:38,433
for plants to thrive
much farther inland.

473
00:31:42,366 --> 00:31:46,800
Their wind-borne spores
reach drier upland areas.

474
00:31:46,800 --> 00:31:53,633
♪ ♪

475
00:31:53,633 --> 00:31:56,066
Without the barrier that kept

476
00:31:56,066 --> 00:31:59,000
terrestrial plant life
near the water's edge,

477
00:31:59,000 --> 00:32:03,333
plants scale new heights,

478
00:32:03,333 --> 00:32:07,166
and diversify
as they occupy new environments.

479
00:32:07,166 --> 00:32:10,033
♪ ♪

480
00:32:10,033 --> 00:32:13,433
For the first time,

481
00:32:13,433 --> 00:32:17,933
significant parts of Earth's
land are turning green.

482
00:32:20,400 --> 00:32:22,000
FIELD:
Plants changed our landscape

483
00:32:22,000 --> 00:32:24,100
by terra-forming bare rock

484
00:32:24,100 --> 00:32:25,466
into living matter.

485
00:32:25,466 --> 00:32:27,033
Life and Earth,

486
00:32:27,033 --> 00:32:28,433
they're not separate entities--

487
00:32:28,433 --> 00:32:30,000
they're totally interconnected.

488
00:32:36,500 --> 00:32:38,933
So, these changes that plants
caused to the Earth's surface

489
00:32:38,933 --> 00:32:40,566
had huge consequences.

490
00:32:40,566 --> 00:32:43,233
Pretty much everything
about the landscape

491
00:32:43,233 --> 00:32:48,166
was influenced
by plants moving onto the land.

492
00:32:48,166 --> 00:32:51,466
NARRATOR:
But plants don't
just alter Earth's surface.

493
00:32:51,466 --> 00:32:54,433
♪ ♪

494
00:32:54,433 --> 00:32:56,900
CARVALHO:
As plants are creating

495
00:32:56,900 --> 00:32:59,133
this beautiful green planet,

496
00:32:59,133 --> 00:33:01,433
carbon dioxide levels in the
atmosphere

497
00:33:01,433 --> 00:33:04,066
actually start going down.

498
00:33:04,066 --> 00:33:07,133
Part of the reason
has to do with plants.

499
00:33:07,133 --> 00:33:08,700
As plants are growing,

500
00:33:08,700 --> 00:33:11,033
they're accumulating
carbon dioxide

501
00:33:11,033 --> 00:33:12,966
as they're transforming it
into sugars,

502
00:33:12,966 --> 00:33:14,766
and making up
their plant bodies.

503
00:33:14,766 --> 00:33:18,400
As plants had exploded across
the landscape,

504
00:33:18,400 --> 00:33:23,466
CO2 in the atmosphere
decreased by upwards of 25%.

505
00:33:24,733 --> 00:33:28,333
NARRATOR:
Ironically, this
poses a problem to plants.

506
00:33:32,633 --> 00:33:36,466
Because carbon dioxide
is plant food.

507
00:33:40,000 --> 00:33:43,566
They absorb the CO2
for photosynthesis

508
00:33:43,566 --> 00:33:47,700
through structures
called stomata.

509
00:33:49,333 --> 00:33:51,633
CONTRERAS:
Stomata are these cellular
complexes

510
00:33:51,633 --> 00:33:53,666
that have a pore in the middle,

511
00:33:53,666 --> 00:33:55,733
and these are the gas exchange
pores for plants,

512
00:33:55,733 --> 00:33:58,200
so it's the way they move
carbon dioxide

513
00:33:58,200 --> 00:34:00,866
in and out of the plant body.

514
00:34:02,666 --> 00:34:05,933
If you look at stomata under the
microscope, it almost looks like

515
00:34:05,933 --> 00:34:09,733
they're breathing
as they open and close.

516
00:34:09,733 --> 00:34:11,533
JOHNSON:
In early land plants,

517
00:34:11,533 --> 00:34:14,033
between 420 and 390 million
years ago,

518
00:34:14,033 --> 00:34:16,400
most land plants had

519
00:34:16,400 --> 00:34:18,700
their stomata on their stems.

520
00:34:18,700 --> 00:34:20,966
The falling carbon dioxide
levels

521
00:34:20,966 --> 00:34:24,133
had a huge impact on plants.

522
00:34:24,133 --> 00:34:26,600
In order to get as much
carbon dioxide

523
00:34:26,600 --> 00:34:30,100
as they were before,
they would need more stomata.

524
00:34:30,100 --> 00:34:31,433
But where to put them?

525
00:34:33,533 --> 00:34:37,933
CONTRERAS:
The answer was as elegant
as it was revolutionary.

526
00:34:37,933 --> 00:34:42,433
♪ ♪

527
00:34:42,433 --> 00:34:44,800
Leaves.

528
00:34:49,866 --> 00:34:52,533
♪ ♪

529
00:34:52,533 --> 00:34:55,233
NARRATOR:
Leaves came about as an
adaptation

530
00:34:55,233 --> 00:34:59,800
to cope with
the changing atmosphere.

531
00:34:59,800 --> 00:35:01,733
Leaves make plants more
efficient

532
00:35:01,733 --> 00:35:03,733
by providing
greater surface area

533
00:35:03,733 --> 00:35:08,633
for photosynthesis and for
taking up CO2 for gas exchange.

534
00:35:11,433 --> 00:35:15,066
♪ ♪

535
00:35:15,066 --> 00:35:17,066
NARRATOR:
In a relatively short time,

536
00:35:17,066 --> 00:35:20,133
most plants
had evolved leaves,

537
00:35:20,133 --> 00:35:23,433
but this seemingly
small innovation would trigger

538
00:35:23,433 --> 00:35:26,800
an entirely new dynamic
between plants.

539
00:35:31,200 --> 00:35:33,366
When we have plants
growing close to each other,

540
00:35:33,366 --> 00:35:35,700
these big surfaces
that capture sunlight

541
00:35:35,700 --> 00:35:39,566
are creating competition because
of the shading of each other.

542
00:35:42,900 --> 00:35:45,633
NARRATOR:
This started a race for light

543
00:35:45,633 --> 00:35:51,300
that will ultimately transform
the landscape once again.

544
00:35:51,300 --> 00:35:56,333
♪ ♪

545
00:36:03,533 --> 00:36:06,833
With leaves supporting this
increased photosynthesis,

546
00:36:06,833 --> 00:36:09,233
some plants begin building
their bodies

547
00:36:09,233 --> 00:36:14,233
out of tougher
biological material,

548
00:36:14,233 --> 00:36:16,733
wood,

549
00:36:16,733 --> 00:36:20,833
which leads to the rise of a
whole new type of organism--

550
00:36:20,833 --> 00:36:23,733
biological machines unlike
anything

551
00:36:23,733 --> 00:36:26,433
Earth has seen before.

552
00:36:26,433 --> 00:36:30,600
Trees are photosynthesizing
powerhouses.

553
00:36:30,600 --> 00:36:33,700
With strong wooden trunks,
they can grow much taller,

554
00:36:33,700 --> 00:36:36,133
effectively pushing
past the competition

555
00:36:36,133 --> 00:36:38,966
towards the sunlight they need.

556
00:36:42,166 --> 00:36:44,233
Trees were a huge step forward

557
00:36:44,233 --> 00:36:46,000
for terrestrial plant life.

558
00:36:46,000 --> 00:36:47,600
Trees were remarkable

559
00:36:47,600 --> 00:36:49,933
at exploiting resources.

560
00:36:49,933 --> 00:36:51,533
They had enormous, deep
rooting systems,

561
00:36:51,533 --> 00:36:53,866
allowing them
to access water and nutrients,

562
00:36:53,866 --> 00:36:57,233
they had these giant stems for
stability, and on top of that,

563
00:36:57,233 --> 00:36:59,833
a canopy of leaves
for photosynthesis.

564
00:37:01,466 --> 00:37:03,833
Archaeopteris, like this one
here,

565
00:37:03,833 --> 00:37:06,933
was one of the earliest trees,

566
00:37:06,933 --> 00:37:09,733
and they formed many
of the Earth's first forests.

567
00:37:11,566 --> 00:37:15,833
Here's one branch of
Archaeopteris.

568
00:37:15,833 --> 00:37:17,233
It has big woody stems,

569
00:37:17,233 --> 00:37:20,166
but the leaves kind of look
like ferns,

570
00:37:20,166 --> 00:37:22,466
but kind of not.

571
00:37:22,466 --> 00:37:23,966
BAUMGARTNER:
The ability of Archaeopteris

572
00:37:23,966 --> 00:37:26,666
to consume vast amounts of
carbon dioxide

573
00:37:26,666 --> 00:37:28,700
allowed them to grow to be

574
00:37:28,700 --> 00:37:30,133
almost 100 feet tall.

575
00:37:30,133 --> 00:37:35,600
♪ ♪

576
00:37:35,600 --> 00:37:38,266
JOHNSON:
I often like to say
that trees are made out of gas.

577
00:37:38,266 --> 00:37:43,366
They absorb carbon dioxide
from the atmosphere

578
00:37:43,366 --> 00:37:46,733
to make the carbohydrate
in their plant bodies.

579
00:37:48,866 --> 00:37:53,900
♪ ♪

580
00:38:00,100 --> 00:38:04,066
NARRATOR:
Earth is on its way
to becoming a forest world.

581
00:38:06,400 --> 00:38:11,433
♪ ♪

582
00:38:16,966 --> 00:38:21,266
The Prototaxites are gone,
never to return.

583
00:38:23,900 --> 00:38:28,933
♪ ♪

584
00:38:31,600 --> 00:38:35,600
And the majority of the fungi
retreats from the surface,

585
00:38:35,600 --> 00:38:40,833
thriving in giant networks
below the ground,

586
00:38:40,833 --> 00:38:44,500
where they have remained
ever since,

587
00:38:44,500 --> 00:38:47,600
a vital partner
to the plant life above them.

588
00:38:50,366 --> 00:38:52,500
The spread of plants
from the water's edge

589
00:38:52,500 --> 00:38:55,800
across the planet's surface
is dramatic.

590
00:39:05,100 --> 00:39:10,366
♪ ♪

591
00:39:10,366 --> 00:39:13,966
Plants transform
the face of the planet.

592
00:39:17,000 --> 00:39:18,900
But in doing so,

593
00:39:18,900 --> 00:39:23,233
they also set the stage
for global upheaval.

594
00:39:27,933 --> 00:39:33,833
♪ ♪

595
00:39:33,833 --> 00:39:37,766
This beautiful coastal
redwood forest

596
00:39:37,766 --> 00:39:40,233
is part of a dynamic ecosystem,

597
00:39:40,233 --> 00:39:42,433
with trees playing
an essential role,

598
00:39:42,433 --> 00:39:47,666
even after they can
no longer stand tall.

599
00:39:47,666 --> 00:39:51,500
A fallen coastal redwood
locals call the Phoenix Tree

600
00:39:51,500 --> 00:39:53,966
is a rare instance of being able
to see

601
00:39:53,966 --> 00:39:57,833
the interconnectedness
of the forests above the ground.

602
00:40:00,400 --> 00:40:03,233
So this tree fell over about
86 years ago,

603
00:40:03,233 --> 00:40:04,433
and the special thing about it

604
00:40:04,433 --> 00:40:06,000
is that that wasn't a death
sentence.

605
00:40:07,566 --> 00:40:09,366
Instead,
beneath each separate branch

606
00:40:09,366 --> 00:40:11,433
are roots that are forming,

607
00:40:11,433 --> 00:40:13,966
and these branches are
eventually going to become

608
00:40:13,966 --> 00:40:17,000
their own independent trees.

609
00:40:18,066 --> 00:40:23,700
♪ ♪

610
00:40:23,700 --> 00:40:25,533
These spread-out, shallow roots

611
00:40:25,533 --> 00:40:27,633
allow them to basically
hold hands with each other

612
00:40:27,633 --> 00:40:30,900
for stability, and they can
even share resources

613
00:40:30,900 --> 00:40:33,200
like water and nutrients.

614
00:40:34,733 --> 00:40:38,100
NARRATOR:
But this tree is just
one small piece

615
00:40:38,100 --> 00:40:41,300
of a vast
and interconnected system.

616
00:40:41,300 --> 00:40:43,733
It's a living bridge
that connects the atmosphere

617
00:40:43,733 --> 00:40:46,866
with the soil
and the life within it.

618
00:40:48,766 --> 00:40:51,066
When trees are alive,
they are homes,

619
00:40:51,066 --> 00:40:53,433
they are food,
and they provide moisture

620
00:40:53,433 --> 00:40:55,366
to the environment around them.

621
00:40:57,900 --> 00:40:59,100
But they actually
provide the same things

622
00:40:59,100 --> 00:41:00,433
after they've decomposed.

623
00:41:05,266 --> 00:41:08,100
NARRATOR:
Dead trees are broken down
by organisms

624
00:41:08,100 --> 00:41:10,400
that return the carbon
that was locked in them

625
00:41:10,400 --> 00:41:13,466
back into the atmosphere
through respiration.

626
00:41:14,600 --> 00:41:19,366
And this equilibrium helps keep
the atmospheric CO2 in balance.

627
00:41:26,233 --> 00:41:28,700
But around
350 million years ago,

628
00:41:28,700 --> 00:41:32,433
that balance was interrupted.

629
00:41:34,633 --> 00:41:37,933
Leading to a crisis
that would threaten the survival

630
00:41:37,933 --> 00:41:40,233
of all life on Earth.

631
00:41:42,733 --> 00:41:47,233
♪ ♪

632
00:41:53,200 --> 00:41:56,100
The rapid spread of
terrestrial plant life

633
00:41:56,100 --> 00:41:59,666
has left Earth a changed planet.

634
00:42:03,066 --> 00:42:07,366
In the Southern Hemisphere,
ice sheets form.

635
00:42:09,866 --> 00:42:13,166
But in the equatorial regions,

636
00:42:13,166 --> 00:42:17,800
the climate is still very hot
and wet.

637
00:42:17,800 --> 00:42:22,833
♪ ♪

638
00:42:28,333 --> 00:42:32,033
As the ice sheets expand
and contract,

639
00:42:32,033 --> 00:42:35,033
over millions of years,
sea levels fluctuate,

640
00:42:35,033 --> 00:42:37,800
creating huge deltas

641
00:42:37,800 --> 00:42:40,566
where vast swamp forests
spring up...

642
00:42:43,933 --> 00:42:48,266
...covering millions
of square miles...

643
00:42:50,666 --> 00:42:54,766
...and giving rise to a whole
host of new plant species

644
00:42:54,766 --> 00:42:57,933
that thrive
in these wet conditions.

645
00:43:01,666 --> 00:43:04,366
The largest among them,
Lepidodendrons,

646
00:43:04,366 --> 00:43:07,566
grow over 160 feet tall.

647
00:43:11,833 --> 00:43:14,500
These are part
of a group called lycopods,

648
00:43:14,500 --> 00:43:16,600
or scale trees.

649
00:43:20,633 --> 00:43:23,533
It looks like it's not a plant.

650
00:43:23,533 --> 00:43:25,400
People often find these things,
say,

651
00:43:25,400 --> 00:43:26,800
"These thing's got scales.

652
00:43:26,800 --> 00:43:28,800
"It looks like a garfish,
or a dinosaur,

653
00:43:28,800 --> 00:43:31,433
or some kind of snake,
a reptile."

654
00:43:31,433 --> 00:43:34,433
And in fact,
these are called scale trees.

655
00:43:38,433 --> 00:43:40,933
NARRATOR:
The swamp forests these trees
grew in

656
00:43:40,933 --> 00:43:44,000
would've looked
similar to today's,

657
00:43:44,000 --> 00:43:46,966
except those trees would've
grown incredibly quickly,

658
00:43:46,966 --> 00:43:48,700
creating a huge amount

659
00:43:48,700 --> 00:43:52,566
of plant mass
in a very short time.

660
00:43:52,566 --> 00:43:55,600
HETHERINGTON:
Lepidendron trees could be
enormous,

661
00:43:55,600 --> 00:43:56,866
and one hypothesis is
that they reach

662
00:43:56,866 --> 00:44:00,900
this amazing height
in as little as 15 years.

663
00:44:02,066 --> 00:44:03,900
So this rapid plant growth

664
00:44:03,900 --> 00:44:05,933
would've removed enormous
amounts

665
00:44:05,933 --> 00:44:08,700
 
of carbon dioxide from
the atmosphere.

666
00:44:10,233 --> 00:44:11,933
NARRATOR:
But this was not the only impact

667
00:44:11,933 --> 00:44:15,900
these trees
had on the atmosphere.

668
00:44:15,900 --> 00:44:17,700
CARVALHO:
So when these massive trees

669
00:44:17,700 --> 00:44:21,266
fell into waterlogged
conditions,

670
00:44:21,266 --> 00:44:23,500
which typically are very low
in oxygen,

671
00:44:23,500 --> 00:44:26,366
they become really, really hard
to break down.

672
00:44:26,366 --> 00:44:27,533
Through time,

673
00:44:27,533 --> 00:44:29,133
all this organic matter
accumulates.

674
00:44:32,900 --> 00:44:36,600
NARRATOR:
This huge amount of plant mass
was not broken down

675
00:44:36,600 --> 00:44:40,833
and returned to the atmosphere,
as typically happens today.

676
00:44:40,833 --> 00:44:42,500
Instead, it was locked away

677
00:44:42,500 --> 00:44:46,066
in the sludge of the
swamp forests.

678
00:44:47,866 --> 00:44:49,633
This would have immense
consequences

679
00:44:49,633 --> 00:44:51,133
for the Earth's climate.

680
00:44:51,133 --> 00:44:56,166
♪ ♪

681
00:44:57,866 --> 00:45:00,633
NARRATOR:
The deep basins
of the tropical swamp forests

682
00:45:00,633 --> 00:45:03,133
were log-jammed with
fallen trees

683
00:45:03,133 --> 00:45:06,633
and partially decayed plant
matter that formed peat.

684
00:45:08,700 --> 00:45:11,500
This carbon-rich mixture
was then buried

685
00:45:11,500 --> 00:45:15,933
and compressed under millions
of tons of marine sediment,

686
00:45:15,933 --> 00:45:18,200
deposited by
fluctuating sea levels.

687
00:45:20,500 --> 00:45:24,100
All the ingredients were
in place,

688
00:45:24,100 --> 00:45:25,900
slowly transforming...

689
00:45:25,900 --> 00:45:29,666
(birds squawking)

690
00:45:29,666 --> 00:45:31,200
...into an incredible type
of rock.

691
00:45:42,000 --> 00:45:44,833
We can see that substance
in the black seam

692
00:45:44,833 --> 00:45:48,366
behind me, within the cliff
face, within the rock records.

693
00:45:48,366 --> 00:45:52,400
And that substance
is actually coal.

694
00:45:55,000 --> 00:45:57,366
And this coal forms
when that plant material

695
00:45:57,366 --> 00:45:58,966
is buried within the Earth

696
00:45:58,966 --> 00:46:00,866
and subjected to the Earth's
intense heat

697
00:46:00,866 --> 00:46:02,366
and the intense pressure.

698
00:46:02,366 --> 00:46:06,666
And it forms this midnight
black, energy-rich material.

699
00:46:08,366 --> 00:46:11,200
So coal is very, very rich
in carbon,

700
00:46:11,200 --> 00:46:13,633
and it's this period
of geological time

701
00:46:13,633 --> 00:46:15,300
which is associated with the
deposition

702
00:46:15,300 --> 00:46:17,200
of these thick coal deposits,

703
00:46:17,200 --> 00:46:19,166
so it's no surprise
that this period got its name,

704
00:46:19,166 --> 00:46:22,066
the Carboniferous, which means
coal-bearing or coal-producing.

705
00:46:22,066 --> 00:46:27,200
♪ ♪

706
00:46:27,200 --> 00:46:30,333
NARRATOR:
During the 60 million years
of the Carboniferous,

707
00:46:30,333 --> 00:46:34,233
plant life locked away
100 billion tons

708
00:46:34,233 --> 00:46:39,233
of carbon per year
in the form of coal.

709
00:46:39,233 --> 00:46:40,766
JACKSON:
We know that present day,

710
00:46:40,766 --> 00:46:43,666
the burning of coal is having
a dramatic impact

711
00:46:43,666 --> 00:46:46,366
on the Earth's climate,
but actually,

712
00:46:46,366 --> 00:46:48,333
the formation of coal back in
the Carboniferous

713
00:46:48,333 --> 00:46:53,233
had an equally
as profound effect.

714
00:46:53,233 --> 00:46:56,633
NARRATOR:
With so much plant matter
locked away underground,

715
00:46:56,633 --> 00:46:59,866
atmospheric
carbon levels dropped.

716
00:46:59,866 --> 00:47:02,400
And this is why massive
sustained coal production

717
00:47:02,400 --> 00:47:06,100
kicked the whole system
out of balance.

718
00:47:09,533 --> 00:47:13,000
NARRATOR:
And the impact was dramatic.

719
00:47:13,000 --> 00:47:18,033
♪ ♪

720
00:47:21,966 --> 00:47:23,500
Over millions of years,

721
00:47:23,500 --> 00:47:27,666
CO2 levels plummet, and
global temperatures nosedive,

722
00:47:27,666 --> 00:47:30,533
in a reverse
of the greenhouse effect...

723
00:47:32,866 --> 00:47:34,966
(wind howling)

724
00:47:34,966 --> 00:47:38,166
...causing vast icy expanses.

725
00:47:42,733 --> 00:47:44,666
The consequences
of carbon hoarding

726
00:47:44,666 --> 00:47:46,833
by the equatorial swamp forests

727
00:47:46,833 --> 00:47:49,733
leave plants
teetering on the edge.

728
00:47:53,433 --> 00:47:57,433
In the frozen south,
the forests die off en masse.

729
00:48:03,266 --> 00:48:07,133
SOREGHAN:
As carbon dioxide
continued to drop,

730
00:48:07,133 --> 00:48:09,466
it would've become very,
very cold,

731
00:48:09,466 --> 00:48:12,100
and up to a quarter of the
world's landmasses

732
00:48:12,100 --> 00:48:14,466
would've been covered in ice.

733
00:48:16,733 --> 00:48:18,666
NARRATOR:
If this process had continued,

734
00:48:18,666 --> 00:48:21,200
it would've
had dire consequences.

735
00:48:23,666 --> 00:48:26,033
It could've potentially caused
a Snowball Earth,

736
00:48:26,033 --> 00:48:28,200
or what we call
a runaway glaciation,

737
00:48:28,200 --> 00:48:34,466
where ice could have
covered the entire planet.

738
00:48:36,533 --> 00:48:39,466
NARRATOR:
Which would've set plants back

739
00:48:39,466 --> 00:48:42,366
hundreds of millions of years.

740
00:48:45,100 --> 00:48:48,333
But that isn't what happens.

741
00:48:52,766 --> 00:48:55,200
Beneath the frozen surface,

742
00:48:55,200 --> 00:48:57,566
the giant tectonic plates
are continuing

743
00:48:57,566 --> 00:49:00,133
their perpetual movement.

744
00:49:02,300 --> 00:49:06,466
SOREGHAN:
Over the 60 million years
or so of the Carboniferous,

745
00:49:06,466 --> 00:49:09,066
plate tectonics
had been creating

746
00:49:09,066 --> 00:49:11,666
a new supercontinent.

747
00:49:11,666 --> 00:49:13,133
They were zippering together,

748
00:49:13,133 --> 00:49:17,100
essentially along the Equator,
and moving northward.

749
00:49:17,100 --> 00:49:19,066
Mountains were being formed,

750
00:49:19,066 --> 00:49:21,400
new weather patterns were
being altered

751
00:49:21,400 --> 00:49:23,333
and adjusted as a result

752
00:49:23,333 --> 00:49:26,300
of this change
in the landmass on Earth.

753
00:49:30,133 --> 00:49:32,333
NARRATOR:
And with this change...

754
00:49:32,333 --> 00:49:35,000
♪ ♪

755
00:49:35,000 --> 00:49:38,566
...about 300 million years ago,

756
00:49:38,566 --> 00:49:43,933
most of the swamps dry up and
cease their production of coal.

757
00:49:45,533 --> 00:49:47,000
SOREGHAN:
When coal formation

758
00:49:47,000 --> 00:49:49,666
essentially ended, it meant that

759
00:49:49,666 --> 00:49:52,300
we weren't locking away as much
carbon dioxide,

760
00:49:52,300 --> 00:49:58,766
and yet, volcanoes were
still belching out CO2,

761
00:49:58,766 --> 00:50:01,300
but we weren't
drawing it down as much.

762
00:50:01,300 --> 00:50:04,166
And therefore carbon dioxide
began rising

763
00:50:04,166 --> 00:50:06,366
in the atmosphere,
the Earth began warming...

764
00:50:09,000 --> 00:50:11,333
...and the glaciers started
melting.

765
00:50:11,333 --> 00:50:15,633
♪ ♪

766
00:50:19,066 --> 00:50:23,166
NARRATOR:
The ice sheets recede
and eventually disappear.

767
00:50:25,100 --> 00:50:29,766
This set the stage
for a plant renaissance.

768
00:50:29,766 --> 00:50:32,033
Plant life
exploded in diversity,

769
00:50:32,033 --> 00:50:36,366
leading eventually
to the green world we see today.

770
00:50:36,366 --> 00:50:41,966
NARRATOR:
Over the following
few hundred million years,

771
00:50:41,966 --> 00:50:46,366
plants would overcome
one challenge after another,

772
00:50:46,366 --> 00:50:52,466
developing flowers
and fruit,

773
00:50:52,466 --> 00:50:55,233
co-evolving with insects,

774
00:50:55,233 --> 00:50:58,033
and eventually
forming grasses and grains.

775
00:50:59,900 --> 00:51:02,633
Plants transform the land from
green

776
00:51:02,633 --> 00:51:05,500
into every vivid color of the
spectrum.

777
00:51:05,500 --> 00:51:07,833
♪ ♪

778
00:51:07,833 --> 00:51:09,600
NARRATOR:
Earth's transformation

779
00:51:09,600 --> 00:51:13,466
from a barren, rocky world
to the living planet

780
00:51:13,466 --> 00:51:16,466
we see today is spectacular.

781
00:51:18,333 --> 00:51:22,033
Rocks breathed life
into the land,

782
00:51:22,033 --> 00:51:25,200
but then life altered the rocks,
and changed them,

783
00:51:25,200 --> 00:51:28,666
and diversified and enriched our
planet in so many ways.

784
00:51:28,666 --> 00:51:31,666
If plants hadn't conquered the
land,

785
00:51:31,666 --> 00:51:34,966
 
we definitely
would not be here today.

786
00:51:34,966 --> 00:51:38,566
BAUMGARTNER:
The chair that I am
sitting in is from plants.

787
00:51:38,566 --> 00:51:39,966
The food that you eat,

788
00:51:39,966 --> 00:51:41,500
the clothes that you wear,

789
00:51:41,500 --> 00:51:43,900
everything you know

790
00:51:43,900 --> 00:51:45,900
is because of plants.

791
00:51:45,900 --> 00:51:50,700
♪ ♪

792
00:51:50,700 --> 00:51:52,733
So, no matter how we try,

793
00:51:52,733 --> 00:51:54,333
we can't escape the fact

794
00:51:54,333 --> 00:51:56,533
that this is a plant planet.

795
00:51:56,533 --> 00:52:00,733
♪ ♪

796
00:52:08,433 --> 00:52:10,000
NARRATOR:
On "NOVA: Ancient Earth"...

797
00:52:10,000 --> 00:52:11,233
PAUL WIGNALL:
It's the mother
of mass extinctions.

798
00:52:11,233 --> 00:52:12,900
Something utterly catastrophic.

799
00:52:12,900 --> 00:52:14,200
SURESH SINGH:
Much greater than the one

800
00:52:14,200 --> 00:52:15,533
that ended the age
of the dinosaurs.

801
00:52:15,533 --> 00:52:18,066
Now we finally know the culprit.

802
00:52:18,066 --> 00:52:20,400
(explosion pounds)

803
00:52:20,400 --> 00:52:22,266
JEFFREY BENCA:
We are finally able to piece
together clues

804
00:52:22,266 --> 00:52:24,266
from this ancient crime scene.

805
00:52:24,266 --> 00:52:26,666
SINGH:
We're talking wildfires,
acid rain,

806
00:52:26,666 --> 00:52:28,266
deadly U.V. radiation.

807
00:52:28,266 --> 00:52:30,066
This was hell on Earth.

808
00:52:30,066 --> 00:52:33,366
NARRATOR:
"Inferno" on "NOVA."

809
00:52:33,366 --> 00:52:34,966
Next time.

810
00:52:34,966 --> 00:52:37,000
SINGER:
♪ Wish I could go back in time ♪

811
00:52:48,200 --> 00:52:55,733
♪ ♪

812
00:52:59,566 --> 00:53:07,166
♪ ♪

813
00:53:08,800 --> 00:53:16,333
♪ ♪

814
00:53:17,966 --> 00:53:25,500
♪ ♪

815
00:53:31,233 --> 00:53:38,400
♪ ♪