Comets Probably Seeded Earth's Nitrogen Atmosphere

KentuckyFC writes "One of the biggest puzzles of astrobiology is the origin of the Earth's oceans and atmosphere. One favored theory is that our water is the leftovers from a bombardment of comets early in Earth's history. But the ratio of hydrogen and deuterium in the oceans doesn't match the ratio in the four comets measured so far (Halley's, Hyakutake, Hale-Bopp and C/2002 T7 LINEAR). Now a new analysis of the ratio of nitrogen-14 and 15 isotopes in these comets and on Earth places new limits on how much of our environment could have come from comets. On the one hand, the astronomers who did the work say that no more than a few percent of Earth's water could have come from comets. But on the other, they say that the ratio of nitrogen isotopes in these comets almost exactly matches the ratio in Earth's atmosphere. That suggests that while Earth's oceans must have come from somewhere else, Earth's early atmosphere was probably seeded by comets."

Comments

Tunguska Clouds an Indication?

[eldavojohn]

Recently I submitted a story that's probably not going to be published that claims:

Space.com brings word of a team using new evidence is suggesting that the mysterious 1908 event in Tunguska was a comet despite a team two years ago arguing it was an asteroid. The comet theory does explain the odd phenomenon of the night skies being lit up for several nights following the event all across Europe--about 3,000 miles away. Researchers believe this points to a comet because when the space shuttles launched today pass through the atmosphere they cause or improve the formation of noctilucent clouds. These clouds are so high up (55 miles) they are only made of ice particles and they are only visible at night which gives researchers reason to draw the conclusion that the 300 metric tons of water vapor that the shuttle pumps into the Earth's thermosphere must likely indicate that the thing that hit was loaded with water or ice. This would make it a comet and not an asteroid. This--of course--raises new upper-atmosphere physics problems for the Tunguska event but explains the strange phenomenon over the skies of the world following it. You may remember analysis of Lake Cheko last year in an effort to better understand what happened.

Well, if every comet that hit earth dropped off a little bit of water--even in the form of noctilucent clouds ... it'd take a while but is it really so far fetch to think that ultimately all our water and atmosphere are extra-terrestrial? Probably unlikely but over a long enough time, who knows?

Re:Tunguska Clouds an Indication?

[khayman80]

... it'd take a while but is it really so far fetched to think that ultimately all our water and atmosphere are extra-terrestrial?

The point is that the isotope abundances of the oceans don't match the only four comets that have been observed precisely enough. H20 and HDO are easily distinguished from each other, and deuterium (the "D" in HDO) is quite stable so the isotope abundances shouldn't have changed. We've only measured 4 comets, though, so perhaps other comets more closely resemble our oceans.

Coincidentally, I attended Dr. Goldblatt's fascinating talk at the Fall 2008 AGU conference where he showed that the faint young sun paradox could be mitigated by a higher nitrogen pressure in the primordial atmosphere. Someone in the crowd (a Slashdot user, perhaps?) answered my question about experimental constraints on this pressure by saying that current research involving "raindrops" might produce a constraint soon.

This paper seems like it should be relevant, but I've yet to see a direct connection. If anything, the disparities in the isotope abundances between 15N/14N and D/H seem to imply their origins are (at best) only loosely connected. But unfortunately the guy who shouted "raindrops" didn't have a microphone and he was across a crowded lecture hall, so I don't have the foggiest idea what he meant. Maybe "raindrops" was a brief reference to the "enstatite chondrites" on page 7 of this new paper (the context seems similar, at least). However, Javoy's paper was published in 1986 and my mysterious benefactor definitely said the research was currently underway. Plus, the topic at the time was the total pressure of nitrogen, not the isotope abundance...

Anyone who knows about this subject, please enlighten me!

Nitrogen came from comets . . .

[rattaroaz]

Nitrogen came from comets, and methane came from Uranus.

It is possible, but not certain

[comet63]

The article notes that the ratio of the nitrogen isotopes matches what is in the earths atmosphere. It seems to me, that just makes it possible that the comets are a significant source of the nitrogen on Earth. It is also possible that the nitrogen in the comets and in the atmosphere came from a common source.

Not exactly a new theory: The Big Splash

[icebike]

The theory of comets as a source of water was also published in 1990, by Louis A. Frank.

Not exactly your average crack-pot scientists, Frank was the designer of something like 13 payloads on various launch vehicles in the 80s and 90s.

Frank posits that that small comets still hit the moon and earth almost daily, delivering water virtually every day. These small comets are more like fluffy snowballs, and are small enough not to have much if any radar signature, but their effects upon impact with the atmosphere are visible from above.

http://en.wikipedia.org/wiki/The_Big_Splash_(book)

Excerpt from The Big Splash
by Louis A. Frank with Patrick Huyghe
Published by Birch Lane Press, 1990.
ISBN 1-55972-033-6

http://smallcomets.physics.uiowa.edu/blackspot.html