Name: 【TED-Ed】Could comets be the source of life on Earth? - Justin Dowd
Uploaded: 2015-01-03T08:44:53.000Z
Duration: 3 min 38 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Humans have observed comets  for thousands of years

as their orbits have brought them within visible distance of Earth.

these mysterious lights that  came out of nowhere

were thought to be ill omens of war and famine,

But recent research has revealed that comets may be even more deeply connected

than any of these mythical  explanations suggested.

When you think of our Solar System, you probably imagine the nine,

But beyond Neptune, far from the heat of the Sun,

there is a sparse ring found  formed by icy chunks

ranging from the size  of marbles to that of small planets.

And thousands of times farther at the outer reaches of the Solar System

lies a spherical cloud of small  fragments and gases.

Many of these ancient clumps of stardust are leftovers from the formation

of the Solar System 4.6 billion years ago,

while some of the most distant may even come from a neighboring system.

But sometimes the gravity from  passing planets or stars

beginning a journey that can take up to millions of years.

As the frozen object travels further into the Solar System,

the sun grows from a distant spark to an inferno,

melting the ice for the first time in billions of years.

forming a bright surrounding cloud, called a coma,

that can grow even larger than the sun itself.

Meanwhile, the intense stream of  high-energy particles

constantly emitted by the Sun, known as the solar wind,

blows particles away from  the comet's core,

forming a trail of debris up to millions of miles long.

The ice, gas and dust reflect  light glowing brightly.

A comet is born, now orbiting the sun along with the rest of the objects

But as the comet travels through the Solar System,

the solar wind tears apart and recombines molecules into various compounds.

In some of the compounds that scientists found,

first in the rubble left by a meteorite that disintegrated above northern Canada,

and then in samples collected by a space craft from a passing comet's tail,

were nothing less important than amino acids.

Coming together to form proteins according to the instructs encoded in DNA,

these are the main active components in all living cells,

If comets are where these building blocks of life were first formed,

then they are the ultimate source of life on Earth,

and, perhaps, some of the other places they visited as well.

We know that planets orbit nearly every star in the night sky,

with one in five having a planet similar to Earth in size and temperature.

If Earth-like planets and the molecules found in DNA are not anomalies,

we may be only one  example of what's possible

when a planet under the right conditions is seeded with organic molecules

the comet that first brought  amino acids to Earth

a prediction of a distant future, where creatures of stardust

would return to space to find  the mysteries of where they came from.

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【TED-Ed】Could comets be the source of life on Earth? - Justin Dowd

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