Prática de Shadowing: Where Did Earth's Water Come From? - Aprenda a falar inglês com vídeo

Unlike every other planet in our solar system, Earth's surface is 70 % liquid water, which while useful for life, is also kind of weird,

because everything we know about how and when our planet formed says Earth's surface should be bone dry.

The story goes like this.

Our solar system formed from the collapse of a large cloud of dust and gas.

The dense blob of gas at the center ignited to form the sun, which as a young unstable star unleashed a fierce solar wind.

And over time, this stream of charged particles pushed the remaining gas cloud farther and farther out, leaving only solid particles behind to clump together into rocks,

planetesimals, and finally, the rocky planets of the inner solar system that we know today.

And here's the problem.

Water, in the form of ice, couldn't have been one of the solid particles that stuck around to form our planet, because the early inner solar system was far too hot for frozen water,

and any water vapor would have been blasted away by the solar wind.

So if Earth didn't start off with water, how did we end up with such splendid oceans?

We know H2O wasn't manufactured here over the eons, because natural processes like combustion,

breathing and photosynthesis create and destroy roughly equal amounts of water, and either way, the amounts in question are so minuscule that they can't account for the abundance of water on the planet.

Since Earth's water was neither part of the original package nor manufactured here, it must have flown in from far away, on meteoroids or comets or other bodies originating in the outer solar system,

where they were far enough from the sun for frozen water to survive.

The dirty ice balls we call comets are a logical candidate for the source of our water, but were ruled out when we discovered that they were far richer in heavy hydrogen than earth water.

Heavy hydrogen has a neutron as well as a proton in its nucleus, and for every million hydrogen atoms in earth water, about 150 are heavy ones,

while typical comet water has twice that many.

These mismatched chemical signatures suggest that Earth's water couldn't have arrived on comets.

It turns out that the most likely source for Earth's water is a type of meteorite called a carbonaceous chondrite.

Chondrite is just the name given to the class of stony meteoroids that most commonly strike the Earth.

But only the carbonaceous chondrites contain water, as well as lots of carbon if you couldn't tell from their name.

They have water in them because they formed out beyond the sun's frost line, and what's more, their water has levels of heavy hydrogen similar to that of earth water,

strongly suggesting that these earth crashers are the source of our ice caps, clouds, rivers, and oceans.

And thus the water that turned our planet into a blue marble came, quite literally, out of the blue.

📺 Mesmo canal

Palavra	Pronúncia	Significado
comet substantivo	/ˈkɒmɪt/	cometa
hydrogen substantivo	/ˈhaɪdɹəd͡ʒ(ə)n/	hidrogênio, hidrogénio
chondrite substantivo	/ˈkɒndɹaɪt/	condrito
particle substantivo	/ˈpɑɹtək(ə)l/	partícula
meteoroid substantivo		meteoróide
freeze verbo	/ˈfɹiːz/	gelar, congelar
ignite verbo	/ɪɡˈnaɪt/	incendiar, acender
meteorite substantivo	/ˈmi.ti.əˌɹaɪt/	meteorito
minuscule substantivo	/ˈmɪnəˌskjul/	minúscula
neutron substantivo	/ˈnu.tɹɑn/	nêutron, neutrão
originate verbo	/əˈɹɪd͡ʒɪneɪt/	originar
photosynthesis substantivo	/ˌfoʊ.toʊˈsɪn.θə.sɪs/	fotossíntese
planetesimal substantivo		planetesimal
proton substantivo	/ˈpɹoʊ.tɑn/	próton, protão
unleash verbo	/ʌnˈliʃ/	soltar, separar

Palavra	Significado
rule out verbo	riscar
turn out verbo	terminar

Prática de Shadowing: Where Did Earth's Water Come From? - Aprenda a falar inglês com vídeo

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