WEBVTT

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Billions of years ago 
on the young planet Earth

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simple organic compounds assembled 
into more complex coalitions

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that could grow and reproduce.

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They were the very first life on Earth,

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and they gave rise to every one 
of the billions of species

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that have inhabited our planet since.

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At the time, Earth was almost completely 
devoid

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of what we’d recognize as a suitable 
environment for living things.

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The young planet had widespread 
volcanic activity

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and an atmosphere that created 
hostile conditions.

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So where on Earth could life begin?

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To begin the search for 
the cradle of life,

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it’s important to first understand the 
basic necessities for any life form.

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Elements and compounds essential to life
include hydrogen, methane, nitrogen,

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carbon dioxide, phosphates, and ammonia.

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In order for these ingredients to comingle
and react with each other,

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they need a liquid solvent: water.

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And in order to grow and reproduce,

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all life needs a source of energy.

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Life forms are divided into two camps:

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autotrophs, like plants, that generate 
their own energy,

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and heterotrophs, like animals, that 
consume other organisms for energy.

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The first life form wouldn’t have had 
other organisms to consume, of course,

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so it must have been an autotroph,

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generating energy either from the sun
or from chemical gradients.

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So what locations meet these criteria?

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Places on land or close to the surface 
of the ocean

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have the advantage of access to sunlight.

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But at the time when life began,
the UV radiation on Earth’s surface

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was likely too harsh for life 
to survive there.

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One setting offers protection 
from this radiation

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and an alternative energy source:

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the hydrothermal vents that wind across
the ocean floor,

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covered by kilometers of seawater 
and bathed in complete darkness.

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A hydrothermal vent is a fissure 
in the Earth’s crust

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where seawater seeps into magma 
chambers

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and is ejected back out 
at high temperatures,

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along with a rich slurry of minerals 
and simple chemical compounds.

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Energy is particularly concentrated

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at the steep chemical gradients 
of hydrothermal vents.

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There’s another line of evidence 
that points to hydrothermal vents:

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the Last Universal Common Ancestor 
of life, or LUCA for short.

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LUCA wasn’t the first life form, 
but it’s as far back as we can trace.

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Even so, we don’t actually know what 
LUCA looked like—

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there’s no LUCA fossil, no modern-day 
LUCA still around—

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instead, scientists identified genes that
are commonly found in species

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across all three domains 
of life that exist today.

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Since these genes are shared across 
species and domains,

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they must have been inherited from 
a common ancestor.

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These shared genes tell us that LUCA lived
in a hot, oxygen-free place

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and harvested energy from a chemical 
gradient—

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like the ones at hydrothermal vents.

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There are two kinds of hydrothermal vent:

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black smokers and white smokers.

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Black smokers release acidic, 
carbon-dioxide-rich water,

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heated to hundreds of degrees Celsius
and packed with sulphur, iron, copper,

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and other metals essential to life.

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But scientists now believe that black 
smokers were too hot for LUCA—

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so now the top candidates for the 
cradle of life are white smokers.

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Among the white smokers,

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a field of hydrothermal vents on the 
Mid-Atlantic Ridge called Lost City

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has become the most favored candidate 
for the cradle of life.

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The seawater expelled here is highly 
alkaline and lacks carbon dioxide,

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but is rich in methane and offers 
more hospitable temperatures.

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Adjacent black smokers may have 
contributed the carbon dioxide necessary

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for life to evolve at Lost City,

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giving it all the components to support 
the first organisms

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that radiated into the incredible 
diversity of life on earth today.