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[thunder crashing]

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[rainfall]

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[dog barking]

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[birds calling]

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[varied bird calls]

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[wings fluttering]

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[narrator] The Earth,
home to millions of species.

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[man talking on radio]

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[woman singing]

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00:00:34,720 --> 00:00:37,960
But what might live... beyond?

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Astronomers have discovered 
thousands of planets

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outside our solar system.

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They believe there are trillions more.

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If life exists on only a fraction of them,

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then the universe must be... alive.

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[cawing]

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[chattering]

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All living things have the same needs.

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To feed...

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reproduce...

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and evolve.

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By applying the laws of life on Earth

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to the rest of the universe...

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it's possible to imagine

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what could live...

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on alien worlds.

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Most planets we know of are so hellish,

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it seems impossible 
that anything could live.

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But it's amazing where life can take hold.

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[squelching]

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[woman] For as long as I can remember,
my mom always told me I was an alien,

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because I just had my mind on outer space
from the beginning.

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I just had always known that I wanted
to get out there and explore the universe.

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Oh, my God.

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-[sighs]
-[bleeping]

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This is the most incredible place
I think I've ever seen.

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This is what I dream other planets
looking like.

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It's... it's incredible. [laughs]

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So, yeah.

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[sobs]

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The Danakil Depression
is known locally as "The Gateway to Hell."

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120 meters below sea level and volcanic...

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it's the hottest place on Earth.

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We're at 79C. 82C.

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This one's topping out at 87.

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If life can exist here...

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it could exist on any number of worlds 
in the universe.

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Life on other planets, 
they're gonna have, uh, chemistry.

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Whether it looks exactly like ours,
we don't know,

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but they're gonna have chemistry
that helps them live.

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And that chemistry 
is going to be subject to limits.

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For example, all life is made up 
of cells.

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Inside these cells they have biomolecules

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that allow the cells
to function and live and work.

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That's our machinery that runs
and makes this chemistry happen,

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that keeps life living. [laughs]

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And so we really wanna understand
how that machinery works

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and what's gonna make that machinery
break down.

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Until recently, it was assumed

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that Danakil was too extreme
to support life.

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But astrobiologists come here to look 
for simple single-celled microbes...

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known as extremophiles.

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[Kennda] Microbes are too small
to see with the naked eye,

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so it's not going to be as simple as
taking a little bit of water out of a lake

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and putting it under a microscope 
and seeing lots of teeming bugs.

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The only way to detect
the presence of extremophiles

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is to find traces of their DNA,

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using a portable genetic sequencer.

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This is a very small device 
and it's very sensitive to temperature,

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and we're in one of the hottest places 
on the planet Earth.

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So, here in the field right now,
we do... a cool block,

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to kind of keep it cool,
and we have our channels running.

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[static crackling]

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-[bleeping]
-And we have... [laughs]

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We have sequencing!

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We actually have sequencing happening.

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We have DNA in here. 

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Excellent.

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Sequencing of DNA is proof

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that extremophiles can survive 
in the acidic waters of Danakil.

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These guys are like the superheroes 
of microbes, and it's just amazing,

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as we learn more and more about
the different strategies and mechanisms

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that they come up with to survive 
these kinds of environments.

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Finding things alive here
opens up an intriguing possibility.

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But some life forms are tough enough 
to survive anywhere...

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even in the deepest reaches of space.

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A red dwarf star.

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The most common type of star 
in our galaxy.

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Imagine a planet in such a close orbit,

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its rotation is locked
by the star's gravity,

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so it always shows
the same face to its sun.

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This is Janus.

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How would life adapt
on such an extreme world?

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On one side of the planet,
it's always daytime,

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a searing desert.

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[wind whistling]

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On the other side, it's forever night,

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a frozen shadowland.

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Squeezed between the two,
a sliver of perpetual twilight.

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Freezing meltwater
flows from the cold side,

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carving canyons through the landscape.

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Even here, where the planet's 
most hospitable,

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there's little vegetation.

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But deep in these canyons

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lives an extraordinary
five-legged creature...

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a pentapod.

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No bigger than a cat,

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it's the dominant life form on Janus,

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capable of adapting to any conditions.

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On the cold side,

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it's stocky and hairy.

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On the hot side,
it's shiny, slender and skittish.

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Pentapods can become
whatever they need to be

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in order to survive.

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[grunting]

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On Earth, all animals adapt 
to fit their environment.

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[birdsong]

118
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But some are more adaptable than others.

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[birds cawing]

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[woman] This trail
that I just came across here,

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it's a beautifully manicured trail,

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and you would think it was made by some
bigger animal or maybe even a human.

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But it's actually made by ants.

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The leaf-cutter ant, in particular.

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All looks quiet right now,

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but if we come back at night, this will
actually turn into an ant super-highway,

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00:11:32,760 --> 00:11:36,320
with leaves just streaming up,
like, towards their nest.

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[cicadas chirping]

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Oh, wow.

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Look at that.

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This is the ant nest.

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You can really see 
into the heart of this colony.

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There's a lot going on.

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00:12:07,520 --> 00:12:11,360
There's actually, for leaf-cutter ants,
there's different castes.

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There is the soldiers,
there are different workers.

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There's also the queen.

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She's the only one who's laying eggs,
and there's only a single queen.

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Without her, none of this would be here.

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An ant colony
depends on the division of labor.

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Different castes have different jobs,
and they come in all shapes and sizes.

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[Magdalena] I just grabbed
one of the soldiers,

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00:12:45,920 --> 00:12:48,600
and I also grabbed
the really, really small worker.

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00:12:48,680 --> 00:12:51,400
And it's not the smallest worker
in this colony,

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but it's-- it's pretty close.

145
00:12:53,080 --> 00:12:56,000
And I mean, the soldiers,
I barely can hold her.

146
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It's really hard. I can feel her power.

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I can feel she's trying to get out.  
Her jaws are wide open.

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00:13:02,120 --> 00:13:04,240
But, I mean, the difference is incredible.

149
00:13:04,320 --> 00:13:08,720
And to think that they all started 
from the same-- the same larva.

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00:13:12,120 --> 00:13:15,400
All ants in a colony
are closely related.

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00:13:17,440 --> 00:13:19,800
They share most of the same genes.

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00:13:21,720 --> 00:13:27,280
But as they grow up, some genes
are switched on, others switched off,

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00:13:28,280 --> 00:13:30,360
depending on the food they are fed.

154
00:13:32,440 --> 00:13:37,480
Any of them can become workers,
foragers or soldiers.

155
00:13:41,640 --> 00:13:46,280
So, this ability to create such different
shapes and forms from the same blueprint,

156
00:13:47,040 --> 00:13:49,240
this is actually called polyphenism.

157
00:13:49,320 --> 00:13:52,840
And "poly" just means "many,"
and "phenism" would be "shapes."

158
00:14:01,080 --> 00:14:05,640
Oh, the spider just did exactly 
what I was trying to avoid all night.

159
00:14:05,720 --> 00:14:10,080
She walked exactly into one of these 
trails of these leaf-cutters here.

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00:14:10,520 --> 00:14:12,800
And that's not good news.

161
00:14:13,840 --> 00:14:17,800
So here, you really see the power
of these soldiers and their jaws.

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If something disturbs the colony,

163
00:14:22,640 --> 00:14:26,480
it's their job to come in and get it,
and that's exactly what they did.

164
00:14:34,520 --> 00:14:35,720
But wow.

165
00:14:41,080 --> 00:14:42,640
Aaah! [laughs]

166
00:14:42,720 --> 00:14:45,240
All right, I'm already being attacked.
[chuckles]

167
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Ooh, that's gonna hurt.

168
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They are now coming for me.

169
00:14:54,240 --> 00:14:57,720
So, any creature
that has this ability to morph

170
00:14:57,800 --> 00:15:01,200
and react to changes in its environment
as quickly as ants can do,

171
00:15:01,280 --> 00:15:04,320
has an amazing advantage
to not just survive,

172
00:15:04,400 --> 00:15:06,400
but actually dominate its world.

173
00:15:21,840 --> 00:15:26,280
On Janus,
pentapods are masters of polyphenism.

174
00:15:29,920 --> 00:15:33,680
Like ants, they're able to develop 
into different forms.

175
00:15:37,120 --> 00:15:40,160
But they all begin life
in the same place...

176
00:15:42,840 --> 00:15:44,880
the Twilight Zone.

177
00:15:47,000 --> 00:15:49,320
[wind whistling]

178
00:15:52,600 --> 00:15:55,400
A pair of adults is ready to breed.

179
00:15:56,480 --> 00:15:58,120
[chattering]

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00:15:58,200 --> 00:16:01,160
They're both male and female.

181
00:16:02,720 --> 00:16:04,080
Hermaphrodites.

182
00:16:06,120 --> 00:16:08,360
Each can produce offspring,

183
00:16:09,800 --> 00:16:12,440
doubling their chances of success.

184
00:16:21,960 --> 00:16:24,000
[clicking and chattering]

185
00:16:27,880 --> 00:16:32,680
Having mated, a pentapod
leaves the shelter of the canyon.

186
00:16:36,320 --> 00:16:39,240
It climbs to high ground,

187
00:16:41,400 --> 00:16:43,200
ready to spawn.

188
00:16:49,440 --> 00:16:51,160
[wind whistling]

189
00:16:51,240 --> 00:16:57,400
At the top, a constant wind blows between 
the cold and hot sides of the planet.

190
00:17:09,520 --> 00:17:14,600
But the wind provides an opportunity
to scatter their larvae.

191
00:17:19,240 --> 00:17:22,680
This way, they can colonize the planet.

192
00:17:23,440 --> 00:17:25,440
[fluttering]

193
00:17:35,320 --> 00:17:39,000
On the hot side, water is scarce...

194
00:17:42,280 --> 00:17:45,880
condensing only in shaded areas.

195
00:17:55,920 --> 00:17:59,000
If there's nothing to eat, they move on.

196
00:18:10,240 --> 00:18:14,520
With five legs, 
they can skitter in any direction.

197
00:18:17,320 --> 00:18:18,920
And with ten eyes,

198
00:18:19,360 --> 00:18:21,800
not much escapes their attention.

199
00:18:30,240 --> 00:18:32,040
If they sense a meal, 

200
00:18:32,800 --> 00:18:35,320
they use feelers to root it out.

201
00:18:37,080 --> 00:18:39,080
[squeaking]

202
00:18:41,400 --> 00:18:44,680
They need to make the most
of every opportunity.

203
00:19:02,840 --> 00:19:05,600
Life in any desert is an ordeal.

204
00:19:06,640 --> 00:19:08,920
Only the tough survive.

205
00:19:10,840 --> 00:19:12,680
And in the natural world,

206
00:19:12,760 --> 00:19:14,600
there's nothing much tougher...

207
00:19:15,840 --> 00:19:17,480
than a scorpion.

208
00:19:23,280 --> 00:19:25,000
-Oh. Anything?
-Here?

209
00:19:25,080 --> 00:19:26,320
I don't think so.

210
00:19:32,040 --> 00:19:34,840
[man] My first childhood memory
of the scorpion,

211
00:19:34,920 --> 00:19:39,760
I was, uh, ten years old 
and I see this big scorpion.

212
00:19:41,240 --> 00:19:42,720
I screamed "Mom!"

213
00:19:42,800 --> 00:19:45,520
Uh, so she came to my aid

214
00:19:45,600 --> 00:19:47,880
and she was like,
"What? What happened?"

215
00:19:47,960 --> 00:19:50,840
And I point to the scorpion,
uh, on the ceiling,

216
00:19:50,920 --> 00:19:52,600
I said, "That's gonna eat me."

217
00:19:53,280 --> 00:19:57,360
And she was just like, "No, come on.
Be cool. This is just a scorpion."

218
00:19:58,600 --> 00:20:01,760
So, as a cute Mexican mother,

219
00:20:01,840 --> 00:20:04,240
she took, uh... her sandal

220
00:20:04,320 --> 00:20:08,040
and just smashed
the, uh, little bastard on the ceiling.

221
00:20:17,440 --> 00:20:23,000
Carlos Santibáñez-López
is now an expert on scorpions,

222
00:20:24,120 --> 00:20:26,800
specializing in the study of their venom.

223
00:20:28,720 --> 00:20:32,640
[Carlos] I go at night
and I use the UV light,

224
00:20:32,720 --> 00:20:35,960
because UV light makes scorpions glow.

225
00:20:36,520 --> 00:20:39,280
They have a special protein
in their shell.

226
00:20:40,720 --> 00:20:43,320
Yeah, let's--
Let's take a look at this one.

227
00:20:47,960 --> 00:20:50,720
-Oh, look at this!
-[man] There's a lot of them.

228
00:20:51,240 --> 00:20:52,360
[Carlos] Yeah, this is great.

229
00:20:56,000 --> 00:21:00,560
Scorpions have barely changed
in 400 million years.

230
00:21:01,760 --> 00:21:04,720
Perfectly adapted for life in the desert.

231
00:21:06,360 --> 00:21:10,640
Scorpions have a very slow metabolism.

232
00:21:11,400 --> 00:21:15,560
They can spend
long periods without food or water.

233
00:21:16,920 --> 00:21:20,600
We have records of some species 
lasting one year

234
00:21:21,360 --> 00:21:22,920
without eating anything.

235
00:21:24,160 --> 00:21:27,000
And they have just enough energy

236
00:21:27,080 --> 00:21:30,720
to sustain essential functions
to keep them alive.

237
00:21:32,320 --> 00:21:36,920
They need to ensure 
that the next time food is available,

238
00:21:37,000 --> 00:21:38,280
they catch it.

239
00:21:40,200 --> 00:21:45,680
So, scorpions have developed a lot 
of weapons that they can use to hunt prey,

240
00:21:47,000 --> 00:21:49,520
including the most important weapon...

241
00:21:51,360 --> 00:21:52,280
venom.

242
00:22:09,720 --> 00:22:11,800
To study scorpion venom,

243
00:22:12,680 --> 00:22:16,200
Carlos needs to extract it 
from glands in the tail.

244
00:22:18,720 --> 00:22:25,240
Venom is a powerful cocktail
that contains minerals, salts

245
00:22:25,320 --> 00:22:29,120
and hundreds
of proteins with a different function.

246
00:22:30,240 --> 00:22:32,400
Try to be as fast as you can.

247
00:22:33,200 --> 00:22:34,640
[whispers] There you go.

248
00:22:34,720 --> 00:22:38,200
We use electricity
to stimulate the muscles.

249
00:22:40,920 --> 00:22:44,280
We're only gonna get small...
very small amounts,

250
00:22:44,360 --> 00:22:46,160
a teeny, tiny drop of it.

251
00:22:46,240 --> 00:22:50,040
But this drop is so valuable 
that we don't wanna lose it.

252
00:22:52,320 --> 00:22:54,280
Give him a nice massage.

253
00:22:54,360 --> 00:22:57,040
Yeah. There's a tiny droplet.

254
00:22:58,320 --> 00:23:00,440
-[man] There.
-Oh, yes, it's-- Okay, so it's working.

255
00:23:00,520 --> 00:23:02,000
Uh, we have venom.

256
00:23:02,560 --> 00:23:05,760
It is right there,
but it's a teeny, tiny drop.

257
00:23:06,400 --> 00:23:08,560
-Uh... do you see it?
-[man] That's right. Yeah.

258
00:23:08,640 --> 00:23:11,360
[Carlos] I mean, it's-- 
it's like a-- a drop of water.

259
00:23:21,480 --> 00:23:24,040
Venom is such an effective weapon,

260
00:23:24,640 --> 00:23:28,480
it's used by reptiles, insects and fish.

261
00:23:30,320 --> 00:23:34,600
It has evolved, separately,
at least 30 times.

262
00:23:38,840 --> 00:23:42,560
The more often a trait like venom 
has evolved on Earth,

263
00:23:44,240 --> 00:23:47,640
the more likely it is to exist 
on other planets.

264
00:24:01,440 --> 00:24:03,400
On the hot side of Janus,

265
00:24:03,840 --> 00:24:06,920
pentapods use venom to catch their prey.

266
00:24:08,040 --> 00:24:09,280
[squeaking]

267
00:24:09,360 --> 00:24:10,760
[munching]

268
00:24:13,880 --> 00:24:15,560
[crunching]

269
00:24:16,640 --> 00:24:19,080
But hunting alone is risky.

270
00:24:20,400 --> 00:24:21,920
[squeaking]

271
00:24:23,160 --> 00:24:24,760
[skittering]

272
00:24:27,760 --> 00:24:29,400
[whimpering]

273
00:24:31,320 --> 00:24:35,040
Even a venomous predator is powerless

274
00:24:35,120 --> 00:24:36,920
against a swarm.

275
00:24:39,600 --> 00:24:41,600
[screeching]

276
00:24:44,920 --> 00:24:46,920
[wailing]

277
00:24:49,360 --> 00:24:51,400
[creatures chattering]

278
00:24:54,520 --> 00:24:58,640
On the cold side of the planet,
things are just as tough.

279
00:25:02,920 --> 00:25:07,720
In perpetual darkness
and with no energy from the sun...

280
00:25:09,920 --> 00:25:12,000
how can anything survive?

281
00:25:22,320 --> 00:25:26,520
On Earth,
nearly all life depends on sunlight.

282
00:25:28,440 --> 00:25:29,600
[birdsong]

283
00:25:29,680 --> 00:25:32,760
Plants convert solar energy into food,

284
00:25:34,120 --> 00:25:36,280
which feeds other life forms.

285
00:25:39,520 --> 00:25:42,400
But there are some extraordinary places
on Earth

286
00:25:42,480 --> 00:25:46,120
where life has evolved
without any light.

287
00:25:55,000 --> 00:25:56,320
[bleeping]

288
00:25:57,040 --> 00:25:59,760
[woman] When I contemplate
going in a cave like this,

289
00:25:59,840 --> 00:26:03,200
one of the things I know
is it's an alien environment.

290
00:26:03,280 --> 00:26:05,360
-[woman] It's fogging up a little bit.
-[man] Yeah.

291
00:26:05,440 --> 00:26:08,000
[woman] It is full of good ways to die.

292
00:26:09,160 --> 00:26:14,760
One of the big risks in this cave
is there is a lot of hydrogen sulfide.

293
00:26:15,960 --> 00:26:17,920
Hydrogen sulfide can kill you.

294
00:26:18,000 --> 00:26:19,640
-[Diana] Okay. You ready?
-[man] Yeah.

295
00:26:19,720 --> 00:26:24,080
[Diana] And so my husband comes along
to act as a safety officer.

296
00:26:26,080 --> 00:26:30,760
He's not afraid to pull us out and say,
"Time to go, you've had enough."

297
00:26:49,040 --> 00:26:53,400
Cueva de Villa Luz is a maze
of limestone chambers.

298
00:26:57,680 --> 00:27:01,920
Hydrogen sulfide bubbles up 
from the Earth's crust.

299
00:27:04,160 --> 00:27:10,400
Mixing with oxygen, it forms sulfuric acid
and turns the water milky white.

300
00:27:13,720 --> 00:27:16,960
And yet, some life forms survive,

301
00:27:17,520 --> 00:27:20,080
and even thrive in these conditions.

302
00:27:25,600 --> 00:27:26,840
Snottites...

303
00:27:30,280 --> 00:27:32,800
dripping colonies of bacteria.

304
00:27:38,040 --> 00:27:42,040
[Diana] There are a lot of organisms 
in one snottite.

305
00:27:44,080 --> 00:27:46,880
Instead of relying on photosynthesis,

306
00:27:47,520 --> 00:27:50,960
they are eating hydrogen sulfide

307
00:27:52,160 --> 00:27:55,680
and are using it as their energy source.

308
00:28:01,000 --> 00:28:03,280
-[Diana] Okay, ready to flame?
-[husband] Yep.

309
00:28:04,280 --> 00:28:06,200
[Diana] So, make it nice and sterile.

310
00:28:07,480 --> 00:28:09,560
Okay, cap that, please.

311
00:28:13,800 --> 00:28:15,640
Okay, let's go for this one.

312
00:28:16,400 --> 00:28:17,360
Okay.

313
00:28:18,400 --> 00:28:20,680
Okay. One snottite.

314
00:28:23,520 --> 00:28:26,240
These are some of the best snottites
in the world.

315
00:28:27,200 --> 00:28:28,280
So acidic.

316
00:28:29,080 --> 00:28:31,720
More acidic than car battery acid.

317
00:28:36,400 --> 00:28:39,280
An entire ecosystem has evolved

318
00:28:40,040 --> 00:28:42,200
to feed off the snottites.

319
00:28:44,440 --> 00:28:47,240
Creatures that have never seen daylight.

320
00:28:55,160 --> 00:28:56,160
[Diana] Can you see those?

321
00:28:58,120 --> 00:28:59,360
[husband] Yes, I do.

322
00:29:00,360 --> 00:29:03,560
[Diana] So, there's some really big ones
over here to the right.

323
00:29:05,040 --> 00:29:09,600
So, whenever you see one 
of those white streamers of bacteria,

324
00:29:10,320 --> 00:29:12,200
you'll see a fish go after it.

325
00:29:13,840 --> 00:29:17,680
Okay, here comes some more over there.
See? Here comes a big one, see?

326
00:29:18,360 --> 00:29:20,920
It's coming. There, it got it!

327
00:29:24,960 --> 00:29:28,080
[Diana] Studying life in total darkness

328
00:29:28,160 --> 00:29:33,920
has expanded how we look for life
in other places in the universe.

329
00:29:34,440 --> 00:29:36,600
It's made us think about the fact

330
00:29:36,680 --> 00:29:40,640
that we could find life
in places we never considered.

331
00:29:42,680 --> 00:29:44,320
-[husband] Yep, there we go.
-[Diana] 25.

332
00:29:44,400 --> 00:29:47,200
-[bleeping]
-[husband] 25. It's getting pretty high.

333
00:29:47,280 --> 00:29:48,240
[Diana] All right.

334
00:29:48,320 --> 00:29:50,240
You think we ought to get out of here?

335
00:29:50,320 --> 00:29:51,280
[husband] Yeah.

336
00:30:04,880 --> 00:30:07,800
All life needs some form of energy.

337
00:30:10,040 --> 00:30:13,920
On the hot face of Janus,
it comes from starlight.

338
00:30:17,680 --> 00:30:21,920
On the cold face, 
it comes from deep within.

339
00:30:29,000 --> 00:30:31,320
Geothermal activity.

340
00:30:35,720 --> 00:30:39,560
When volcanic pressure 
forces water to the surface,

341
00:30:40,520 --> 00:30:42,760
there's a flurry of new life...

342
00:30:45,120 --> 00:30:47,800
which stirs pentapods into action.

343
00:31:01,560 --> 00:31:05,800
They're after grubs 
that emerge around geothermal pools.

344
00:31:10,240 --> 00:31:11,640
But it's not so easy.

345
00:31:17,800 --> 00:31:20,200
The grubs have evolved a defense.

346
00:31:21,240 --> 00:31:24,640
They jump and flash a warning signal 
to others...

347
00:31:27,320 --> 00:31:29,880
acting as one to stay alive.

348
00:31:30,000 --> 00:31:32,000
[loud buzzing]

349
00:31:46,120 --> 00:31:50,360
On Earth, some animals 
use light in the same way...

350
00:31:51,120 --> 00:31:53,040
to send signals.

351
00:31:54,440 --> 00:31:56,440
[cicadas chirping]

352
00:32:01,520 --> 00:32:05,080
[woman] Every single point of light
that you see out there is a firefly.

353
00:32:07,160 --> 00:32:10,080
Right as the sun sets,
you'll start to see them come up,

354
00:32:11,240 --> 00:32:13,120
like little sparks rising from a fire.

355
00:32:13,200 --> 00:32:16,760
It's just spectacular, and it only gets
better as the night gets darker.

356
00:32:26,080 --> 00:32:28,680
Fireflies flash as a form 
of communication.

357
00:32:29,720 --> 00:32:32,760
They are among the only land animals

358
00:32:32,840 --> 00:32:35,440
that communicate with light 
of their own making.

359
00:32:39,280 --> 00:32:42,760
Bioluminescence evolved
among fireflies

360
00:32:42,840 --> 00:32:44,600
as a warning to predators

361
00:32:45,320 --> 00:32:50,240
that they're packed with toxins 
and should be given a wide berth.

362
00:32:53,840 --> 00:32:55,200
Now the same mechanism

363
00:32:55,840 --> 00:32:58,000
is used for finding a mate.

364
00:33:01,720 --> 00:33:07,480
So, the firefly produces light from an 
organ on its abdomen called the lantern.

365
00:33:08,280 --> 00:33:11,000
And this organ has an enzyme

366
00:33:11,080 --> 00:33:13,160
that produces one photon of light.

367
00:33:13,240 --> 00:33:15,000
This chemical reaction involves oxygen.

368
00:33:15,080 --> 00:33:18,400
So, by controlling the flow of oxygen 
to their lantern,

369
00:33:18,480 --> 00:33:20,760
they can produce, uh, flashes.

370
00:33:20,840 --> 00:33:22,920
They can turn 
the chemical reaction on and off,

371
00:33:23,000 --> 00:33:27,000
and use these flashes
to communicate with each other.

372
00:33:35,520 --> 00:33:39,720
The males are flying around,
and they're doing little advertisements,

373
00:33:39,800 --> 00:33:43,160
little flashes that say, 
"Here I am. This is me, check me out."

374
00:33:46,040 --> 00:33:49,360
And then the females are waiting on 
the ground below and they're looking up.

375
00:33:51,520 --> 00:33:54,720
And when they see a guy that they like,
they flash back.

376
00:33:57,840 --> 00:34:00,400
And then the male will come over,
he'll flash again.

377
00:34:00,480 --> 00:34:03,080
She flashes back 
and they come together and mate.

378
00:34:04,160 --> 00:34:08,400
So, this is actually
one big flirtatious dance

379
00:34:08,480 --> 00:34:10,600
that we're seeing right here behind us.

380
00:34:13,440 --> 00:34:16,000
Each species creates its own 
little language

381
00:34:16,080 --> 00:34:18,080
that they can use
to find each other in the dark.

382
00:34:20,320 --> 00:34:24,440
But using light to communicate
is inherently risky.

383
00:34:26,440 --> 00:34:31,200
Some species have evolved 
to emit fake signals.

384
00:34:34,920 --> 00:34:39,720
What we have here 
is a predatory Photuris female,

385
00:34:39,800 --> 00:34:43,040
also called femmes fatales,
because they have a reputation

386
00:34:43,120 --> 00:34:46,800
for luring in males of other species 
to eat them.

387
00:34:47,720 --> 00:34:52,560
They can hack in to the communication 
between a male and a female

388
00:34:52,640 --> 00:34:54,600
and use that to her advantage.

389
00:34:56,320 --> 00:34:59,120
So, you can tell 
this is a predatory firefly

390
00:34:59,200 --> 00:35:02,600
because her lantern 
has a different shape to it.

391
00:35:03,640 --> 00:35:07,800
Only two-- two little lines light up, 
almost like an equals sign.

392
00:35:08,520 --> 00:35:12,160
So, basically, a male will be 
flying around looking for a mate

393
00:35:12,240 --> 00:35:15,120
and then when the males flash,
they flash back,

394
00:35:15,200 --> 00:35:17,920
just as if 
they were a female of that species.

395
00:35:18,000 --> 00:35:20,520
So, they're imitating
the females of that other species

396
00:35:20,600 --> 00:35:22,240
to get the male to come over,

397
00:35:22,320 --> 00:35:24,280
but they don't wanna
mate with that male...

398
00:35:25,400 --> 00:35:27,800
she wants to eat that male.

399
00:35:30,400 --> 00:35:34,480
And she proceeds to do so 
in an extremely violent way.

400
00:35:36,360 --> 00:35:38,360
[munching]

401
00:35:39,360 --> 00:35:43,880
This is a classic example
of a predator using mimicry.

402
00:35:48,120 --> 00:35:51,480
One species 
copying the behavior of another...

403
00:35:52,840 --> 00:35:54,720
in order to kill it.

404
00:35:58,960 --> 00:36:00,480
[Avalon] Lying and deceit is...

405
00:36:00,560 --> 00:36:03,520
is pretty widespread
in the animal kingdom, I would say.

406
00:36:04,720 --> 00:36:07,720
And I think it would be on any planet.

407
00:36:17,400 --> 00:36:20,920
[fountains hissing]

408
00:36:23,080 --> 00:36:27,000
On Janus,
the grubs use light to stay alive.

409
00:36:32,040 --> 00:36:35,240
But their system is about to be hacked.

410
00:36:47,040 --> 00:36:52,600
By catching a few grubs, the pentapods
absorb their bioluminescence...

411
00:36:56,120 --> 00:36:58,400
and mimic their warning signals.

412
00:37:04,640 --> 00:37:08,680
The grubs instinctively jump away 
from flashing lights.

413
00:37:10,520 --> 00:37:12,600
But this time, it's a trap.

414
00:37:15,840 --> 00:37:19,000
The pentapods have them 
where they want them.

415
00:37:24,120 --> 00:37:29,200
Again, adaptability is the secret 
to their survival.

416
00:37:42,440 --> 00:37:44,600
But for all creatures on Janus,

417
00:37:45,400 --> 00:37:49,200
existence depends on one key ingredient...

418
00:37:53,000 --> 00:37:56,840
whether in the hot,
cold or twilight worlds.

419
00:37:59,920 --> 00:38:01,080
Water.

420
00:38:20,240 --> 00:38:23,640
[man] Everybody knows the story
of Goldilocks and the Three Bears.

421
00:38:26,440 --> 00:38:29,880
She sneaks into their house 
and tries to eat their porridge.

422
00:38:33,640 --> 00:38:35,480
The first bowl is too hot.

423
00:38:39,680 --> 00:38:41,840
The second bowl is freezing cold.

424
00:38:46,440 --> 00:38:49,720
It's only when she tries the third bowl
that she's happy.

425
00:38:54,840 --> 00:38:58,480
"This one," Goldilocks says,
"is just right."

426
00:39:01,160 --> 00:39:04,120
When we look around the universe
in the search for life, 

427
00:39:04,200 --> 00:39:07,360
we are looking for conditions 
that are "just right."

428
00:39:13,640 --> 00:39:15,760
And "just right," in this case,

429
00:39:16,600 --> 00:39:19,080
is defined by the presence of this stuff.

430
00:39:20,280 --> 00:39:21,400
Water.

431
00:39:27,680 --> 00:39:32,120
Water transports
the essentials for life around the planet

432
00:39:34,760 --> 00:39:37,000
and around every living body.

433
00:39:41,440 --> 00:39:45,120
It's the most important substance 
in the universe.

434
00:39:52,960 --> 00:39:54,800
[man] Because water is so familiar to us,

435
00:39:54,880 --> 00:40:00,360
it's not until you really stop and think 
about it that you realize how weird it is.

436
00:40:00,440 --> 00:40:03,320
Water is made up 
by one oxygen atom...

437
00:40:05,440 --> 00:40:07,320
and two hydrogen atoms.

438
00:40:08,160 --> 00:40:11,600
And because of the nature of the elements
and the way they're bound,

439
00:40:11,680 --> 00:40:15,000
we have a net negative charge 
at the oxygen side

440
00:40:15,080 --> 00:40:16,960
and positive on the two hydrogens.

441
00:40:17,040 --> 00:40:19,440
This means that every hydrogen 
in a molecule

442
00:40:19,520 --> 00:40:22,880
can interact with the oxygen 
on the other molecules neighboring.

443
00:40:23,680 --> 00:40:27,400
Replicate this attraction for billions
of neighboring molecules

444
00:40:27,480 --> 00:40:29,400
and you get 
a substance that is very sticky.

445
00:40:31,800 --> 00:40:34,640
And water molecules
don't just attract each other,

446
00:40:34,720 --> 00:40:38,200
they attract almost any other
molecule they come in contact with.

447
00:40:41,040 --> 00:40:43,280
They pull other substances apart,

448
00:40:43,960 --> 00:40:46,480
break them down, and dissolve them.

449
00:40:59,520 --> 00:41:02,320
Water is the universal solvent

450
00:41:03,440 --> 00:41:07,600
because of its unique ability
to dissolve nutrients and chemicals.

451
00:41:15,840 --> 00:41:21,680
It seems certain the first spark 
of life on Earth happened not on land...

452
00:41:24,040 --> 00:41:25,560
but in water.

453
00:41:31,640 --> 00:41:34,200
[Donato] Deep underwater,
in the primordial oceans,

454
00:41:34,280 --> 00:41:37,560
the chemical ingredients for life
were swirling around.

455
00:41:40,400 --> 00:41:43,840
What was needed was a place 
to concentrate these ingredients...

456
00:41:45,920 --> 00:41:49,560
to allow the chemical reaction
that would eventually lead to life.

457
00:41:52,440 --> 00:41:55,880
That place could have been 
a hydrothermal vent.

458
00:41:59,800 --> 00:42:03,120
Water interacts with hot rocks 
deep underground.

459
00:42:04,120 --> 00:42:07,200
It comes gushing back up 
into the freezing seawater

460
00:42:07,280 --> 00:42:09,280
carrying nutrients and chemicals...

461
00:42:11,360 --> 00:42:13,320
little bubbles of life.

462
00:42:17,440 --> 00:42:21,000
The link between
water and life is so strong,

463
00:42:21,920 --> 00:42:26,320
it's hard to imagine any life
anywhere in the universe

464
00:42:26,400 --> 00:42:28,400
existing without it.

465
00:42:37,520 --> 00:42:39,040
[Donato] It's mind-boggling to think,

466
00:42:39,120 --> 00:42:42,520
you know, how life can find a way 
in very extreme places.

467
00:42:42,600 --> 00:42:43,800
Very hot, very cold.

468
00:42:44,200 --> 00:42:46,480
And at the end, it's all about the water.

469
00:42:46,560 --> 00:42:49,000
If there's liquid water, you'll find life.

470
00:43:00,120 --> 00:43:02,880
Water on Janus is scarce.

471
00:43:05,840 --> 00:43:08,160
It either freezes as ice...

472
00:43:11,240 --> 00:43:13,480
or evaporates into the wind.

473
00:43:18,240 --> 00:43:20,760
But there's just enough liquid water

474
00:43:21,320 --> 00:43:23,120
for life to take hold...

475
00:43:26,320 --> 00:43:28,840
and for the toughest of creatures

476
00:43:29,440 --> 00:43:31,760
to adapt and survive.

477
00:43:33,000 --> 00:43:34,760
[wind howling]

478
00:43:36,280 --> 00:43:38,280
[fluttering]

479
00:43:42,640 --> 00:43:44,920
At NASA, they have a saying.

480
00:43:46,240 --> 00:43:48,240
"If you want to find life...

481
00:43:48,880 --> 00:43:50,600
follow the water."

482
00:43:59,760 --> 00:44:03,080
How might life adapt on a different world?

483
00:44:04,520 --> 00:44:06,440
One with two stars,

484
00:44:09,480 --> 00:44:12,200
where there's more energy than on Earth.

485
00:44:12,880 --> 00:44:14,280
[creatures calling]

486
00:44:15,800 --> 00:44:19,400
A planet perfect for life.