[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Billions of years ago \Non the young planet Earth
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,simple organic compounds assembled \Ninto more complex coalitions
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,that could grow and reproduce.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,They were the very first life on Earth,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and they gave rise to every one \Nof the billions of species
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,that have inhabited our planet since.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,At the time, Earth was almost completely \Ndevoid
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,of what we’d recognize as a suitable \Nenvironment for living things.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,The young planet had widespread \Nvolcanic activity
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and an atmosphere that created \Nhostile conditions.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,So where on Earth could life begin?
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,To begin the search for \Nthe cradle of life,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,it’s important to first understand the \Nbasic necessities for any life form.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Elements and compounds essential to life\Ninclude hydrogen, methane, nitrogen,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,carbon dioxide, phosphates, and ammonia.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,In order for these ingredients to comingle\Nand react with each other,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,they need a liquid solvent: water.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,And in order to grow and reproduce,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,all life needs a source of energy.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Life forms are divided into two camps:
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,autotrophs, like plants, that generate \Ntheir own energy,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and heterotrophs, like animals, that \Nconsume other organisms for energy.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,The first life form wouldn’t have had \Nother organisms to consume, of course,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,so it must have been an autotroph,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,generating energy either from the sun\Nor from chemical gradients.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,So what locations meet these criteria?
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Places on land or close to the surface \Nof the ocean
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,have the advantage of access to sunlight.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,But at the time when life began,\Nthe UV radiation on Earth’s surface
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,was likely too harsh for life \Nto survive there.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,One setting offers protection \Nfrom this radiation
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and an alternative energy source:
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,the hydrothermal vents that wind across\Nthe ocean floor,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,covered by kilometers of seawater \Nand bathed in complete darkness.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,A hydrothermal vent is a fissure \Nin the Earth’s crust
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,where seawater seeps into magma \Nchambers
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and is ejected back out \Nat high temperatures,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,along with a rich slurry of minerals \Nand simple chemical compounds.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Energy is particularly concentrated
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,at the steep chemical gradients \Nof hydrothermal vents.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,There’s another line of evidence \Nthat points to hydrothermal vents:
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,the Last Universal Common Ancestor \Nof life, or LUCA for short.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,LUCA wasn’t the first life form, \Nbut it’s as far back as we can trace.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Even so, we don’t actually know what \NLUCA looked like—
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,there’s no LUCA fossil, no modern-day \NLUCA still around—
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,instead, scientists identified genes that\Nare commonly found in species
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,across all three domains \Nof life that exist today.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Since these genes are shared across \Nspecies and domains,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,they must have been inherited from \Na common ancestor.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,These shared genes tell us that LUCA lived\Nin a hot, oxygen-free place
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and harvested energy from a chemical \Ngradient—
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,like the ones at hydrothermal vents.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,There are two kinds of hydrothermal vent:
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,black smokers and white smokers.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Black smokers release acidic, \Ncarbon-dioxide-rich water,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,heated to hundreds of degrees Celsius\Nand packed with sulphur, iron, copper,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,and other metals essential to life.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,But scientists now believe that black \Nsmokers were too hot for LUCA—
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,so now the top candidates for the \Ncradle of life are white smokers.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Among the white smokers,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,a field of hydrothermal vents on the \NMid-Atlantic Ridge called Lost City
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,has become the most favored candidate \Nfor the cradle of life.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,The seawater expelled here is highly \Nalkaline and lacks carbon dioxide,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,but is rich in methane and offers \Nmore hospitable temperatures.
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,Adjacent black smokers may have \Ncontributed the carbon dioxide necessary
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,for life to evolve at Lost City,
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,giving it all the components to support \Nthe first organisms
Dialogue: 0,9:59:59.99,9:59:59.99,Default,,0000,0000,0000,,that radiated into the incredible \Ndiversity of life on earth today.