Earth May Have Kept Its Own Water Rather Than Getting It From Asteroids (sciencemag.org) 45
sciencehabit writes: Carl Sagan famously dubbed Earth the 'pale blue dot' for our planet's abundant water. But where this water came from—and when it arrived—has been a longstanding debate. Many scientists argue that Earth formed as a dry planet, and gained its water millions of years later through the impact of water-bearing asteroids or comets. But now, scientists say that Earth may have had water from the start, inheriting it directly from the swirling nebula that gave birth to the solar system. If true, the results suggest that water-rich planets may abound in the universe.
Re:God's truth wins again (Score:5, Insightful)
The important question isn't how, but why.
The flying spaghetti monster gave us water so that we could boil pasta.
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The important question isn't how, but why.
The flying spaghetti monster gave us water so that we could boil pasta.
So what your hinting at is that the flying spaghetti monster likes to get eaten?
I guess I can understand that...
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OTOH, Genesis also says that the stars and planets weren't created until the third day (Genesis 1:14). That doesn't jibe with the rather abundant evidence that he/she/it left laying around about the age and evolutionary course of the Universe.
Nothing against the Genesis creation story. On the whole, it's not all that bad a fit to Astronomy, Geology, Paleontology. For a collection of what seems to be complete nonsense, try the Great Flood as described in Genesis chapters 6 thru 9.
Let me suggest that if yo
And water may not always have been water (Score:2)
Other compounds contain Hydrogen
and the early earth had plenty of compounds with oxygen
why not? (Score:3, Interesting)
Thanks to plate tectonics, We don't have much direct information on the early stages of the the Earth's history. But I've never understood why it was assumed that (much of) the Earth's water hasn't been there since our planet coalesced. Of course, I've also never understood the necessity to invoke an improbable planetary collision to explain the moon. It's not like binary pairs of large objects are rare in the universe.
And even if the water did come entirely from cometary impacts after formation, why would that preclude lots of other watery planets? Are comets assumed to be rare in other planetary systems? Why?
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I've also never understood the necessity to invoke an improbable planetary collision to explain the moon. It's not like binary pairs of large objects are rare in the universe.
Earth and the Moon have different compositions. So they can't both have been formed in the same way.
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"Earth and the Moon have different compositions"
As I understand it, the composition of the two bodies is quite similar. In fact that's the primary reason that the collision theory was formulated. In the collision theory, they moon is composed primarily of material blasted from the Earth by the collision. see https://en.wikipedia.org/wiki/... [wikipedia.org]
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Different in the sense that the Earth consists of corey stuff and crusty stuff and the moon only has crusty stuff?
I mean it's not possible that the impact only whacked the outside off, or that whichever fragment got biggest fastest snagged all the heavy shit, is it?
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Well yes. There's a lot written. But there are a horrendous number of loose ends in ALL of them. If I understand correctly, they can't even get a computer model to actually assemble a moon of the correct size in the right place after a modelled collision. Given the ... ahem ... flexibility ... computer modelling, that in itself is a pretty huge difficulty.
Which volatile elements are you thinking of? The two very light gases -- Hydrogen and Helium -- are gone as significant atmospheric components. Is t
Why either - or? (Score:3)
Why couldn't it have been a combination of water from the proto earth and asteroids and comets later on? There's little doubt the earth was bombarded for millions of years after it formed so it seems silly to pretend that didn't deliver any water to the planet.
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"Why couldn't it have been a combination of water from the proto earth and asteroids and comets later on?"
Seems like substantial water contributions from comets would almost certainly have to be the case unless we somehow totally misunderstand the nature and composition of comets or assume that they somehow avoid ever impacting the Earth.
Water(water ice) is plentiful ... (Score:1)
... throughout the solar system, and, by extension, abundant everywhere. Earth formed containing plenty, as every celestial body will. It would have all been fine crystals initially. Now I'll just whip back in my TARDIS and grab some early samples to prove my hypothesis.
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Studying the distant past is difficult, and the science is anything but settled. So we speculate and come up with various hypotheses that we share around. Then we collectively try to punch holes in them and consider their implications - what we'd expect to see today if it were true. We then go looking to see what's actually there. Maybe it supports the hypothesis, maybe it supports the older, more widely accepted story, or maybe it's something completely unexpected that makes you question things you thou
Well.. (Score:1)
Water planets may abound (Score:4, Interesting)
Or if the other theory about asteroids is true, then water-rich planets may abound in the universe. So this changes nothing. Also, both theories explain why all the planets in our solar system are so rich and abundant in water. Except that they are not.
Hydrogen is the most common element in the universe, making up about 3/4 of the mass of the universe. Oxygen is the third most common, but the 2nd most common, Helium, takes up almost 1/4 of the mass of the universe. Oxygen makes up about 1/70th as much mass in the universe as hydrogen. However, somewhat unique on Earth, Oxygen makes up about 64% of the mass of Earth. Atmospheric Oxygen in the other planets is negligible, and even Oxygen combined in other compounds on other planets is a much smaller percentage than on Earth. Oddly, Hydrogen is relatively uncommon on Earth when compared to its abundance in the rest of the universe.
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I doubt very much that oxygen makes up 64% of the mass of the Earth. Do you have a citation?
According to https://en.wikipedia.org/wiki/... [wikipedia.org], the main composition of the Earth by mass is iron at 32.1% though I am somewhat surprised that oxygen is number 2 at 30.1%, which is a lot of oxygen. There are estimates that put the percent of oxygen in the crust at 47% which is close enough to half but still not 64%. And of course the atmosphere is mostly nitrogen at aprox 78% and almost 21% oxygen, thanks to the hard
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Probably just a typo somewhere or if you're like me, a mental hiccup. Shit, I thought that I said by mass for the total and yet I obviously didn't and of course the atmosphere numbers I quoted were by volume which I missed, having found the numbers I remembered.
Don't forget the moon! (Score:4, Interesting)
Isotopic composition (Score:3)
But how did the isotopes get differentially distributed in the primordial cloud, so that the deuterium collected in the outer regions where the comets formed, rather than in the region between Jupiter's orbit and the Sun itself?
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Deuterium has enough of a mass difference with hydrogen that the chemical and physical properties differ a little. Processes that involve adsorption, freezing, and sublimation, like on a comet, can cause small changes in the isotropic ratio. The effect is quite small, but measurable. Even processes like the fixation of carbon by plants can cause measurable changes in isotropic ratio from subtle chemistry differences.
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