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  • [Life will not be contained. Life breaks free. | - Dr. Ian Malcolm in Jurassic Park. Dir. Steven Spielberg]

  • Billions of years ago, on the young planet Earth, simple organic compounds assembled into more complex coalitions that could grow and reproduce.

  • They were the very first life on Earth, and they gave rise to every one of the billions of species that have inhabited our planet since.

  • At the time, Earth was almost completely devoid of what we’d recognize as a suitable environment for living things.

  • The young planet had widespread volcanic activity and an atmosphere that created hostile conditions.

  • So where on Earth could life begin?

  • To begin the search for the cradle of life, it’s important to first understand the basic necessities for any life form.

  • Elements and compounds essential to life include hydrogen, methane, nitrogen, carbon dioxide, phosphates, and ammonia.

  • In order for these ingredients to comingle and react with each other, they need a liquid solvent: water.

  • And in order to grow and reproduce, all life needs a source of energy.

  • Life forms are divided into two camps: autotrophs, like plants, that generate their own energy, and heterotrophs, like animals, that consume other organisms for energy.

  • The first life form wouldn’t have had other organisms to consume, of course, so it must have been an autotroph, generating energy either from the sun or from chemical gradients.

  • So what locations meet these criteria?

  • Places on land or close to the surface of the ocean have the advantage of access to sunlight.

  • But at the time when life began, the UV radiation on Earth’s surface was likely too harsh for life to survive there.

  • One setting offers protection from this radiation and an alternative energy source: the hydrothermal vents that wind across the ocean floor, covered by kilometers of seawater and bathed in complete darkness.

  • A hydrothermal vent is a fissure in the Earth’s crust where seawater seeps into magma chambers and is ejected back out at high temperatures, along with a rich slurry of minerals and simple chemical compounds.

  • Energy is particularly concentrated at the steep chemical gradients of hydrothermal vents.

  • There’s another line of evidence that points to hydrothermal vents: the Last Universal Common Ancestor of life, or LUCA for short.

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

  • Even so, we don’t actually know what LUCA looked likethere’s no LUCA fossil, no modern-day LUCA still around.

  • Instead, scientists identified genes that are commonly found in species across all three domains of life that exist today.

  • Since these genes are shared across species and domains, they must have been inherited from a common ancestor.

  • These shared genes tell us that LUCA lived in a hot, oxygen-free place and harvested energy from a chemical gradientlike the ones at hydrothermal vents.

  • There are two kinds of hydrothermal vent: black smokers and white smokers.

  • Black smokers release acidic, carbon-dioxide-rich water, heated to hundreds of degrees Celsius and packed with sulfur, iron, copper, and other metals essential to life.

  • But scientists now believe that black smokers were too hot for LUCAso now the top candidates for the cradle of life are white smokers.

  • Among the white smokers, a field of hydrothermal vents on the Mid-Atlantic Ridge called Lost City has become the most favored candidate for the cradle of life.

  • The seawater expelled here is highly alkaline and lacks carbon dioxide, but is rich in methane and offers more hospitable temperatures.

  • Adjacent black smokers may have contributed the carbon dioxide necessary for life to evolve at Lost City,

  • giving it all the components to support the first organisms that radiated into the incredible diversity of life on Earth today.

  • Did you know that a single-celled organism caused the first mass extinction? Check out this animation about how it almost wiped out life on earth, and paved the way for complex life.

[Life will not be contained. Life breaks free. | - Dr. Ian Malcolm in Jurassic Park. Dir. Steven Spielberg]

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B2 US TED-Ed hydrothermal life luca earth energy

The mysterious origins of life on Earth - Luka Seamus Wright

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    林宜悉 posted on 2021/10/20
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