Comets Probably Seeded Earth's Nitrogen Atmosphere 110
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."
Tunguska Clouds an Indication? (Score:5, Interesting)
Space.com brings word of a team using new evidence is suggesting that the mysterious 1908 event in Tunguska was a comet [space.com] despite a team two years ago arguing it was an asteroid [slashdot.org]. 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 [wikipedia.org]. 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 [slashdot.org] 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?
The comets may have seeded life. (Score:2, Interesting)
That seems to make some sense. (Score:2, Interesting)
My guess is that earth started out as a (not -so-giant?) gas giant and bled of most of it's original hydrogen. If that's even vaguely true, then there's little likelihood that the isotope mix would be anywhere near what's in comets.
I'm guessing that the deuterium mix is much higher than in comets (because deuterium, being heavier than hydrogen, is less likely to bleed off).
Not exactly a new theory: The Big Splash (Score:5, Interesting)
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) [wikipedia.org]
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 [uiowa.edu]
Re:It is possible, but not certain (Score:3, Interesting)
What comet63 said. Large primoridal clouds of hydrogen are easy to understand, and oxygen is enough lighter than carbon that it could occur early on in stellar formation, I'd think (IANAAP, IMBFOS). So I can imagine large clouds of the two gases igniting in the early part of our planetary history, with enough being captured by our own gravity well to compress and become water. The rest, as they say, is geography. Add lots of the slightly less reactive nitrogen and you'd get something approaching the mixture we're breathing. But in order to seed both the Earth and the Oort cloud, those gas sources would have to be huge. What happened to the rest of it? Blown away on the solar wind? If so, could we see traces like this around other star systems and make a guess about water atmospheres?
Re:Tunguska Clouds an Indication? (Score:4, Interesting)
The May issue of scientific american had an interesting article about the slow loss of atmospheric gasses into space...
how-planets-lose-their-atmospheres [scientificamerican.com] ...which suggests that the early earth had a lot more water and a denser atmosphere. It also, obviously, had a lot more CO2, vast quantities of which are now locked up in the form of rock (limestone) and organic matter.
Re:But there's soooo much water on (and in) Earth. (Score:3, Interesting)
I was under the impression that the Earth's water precipitated out of the original accretion disc as the early earth cooled. That is, everything accreted, and then as the molten rock and surrounding gases cooled to form a sold surface, the water that became the Earth's oceans and such also cooled and condensed, and basically rained down on the planet over time.
Has there been some reason to doubt this? i.e. evidence that refutes this hypothesis?
Re:But there's soooo much water on (and in) Earth. (Score:3, Interesting)
It's easy (unless you're a fundie) to understand where the heavier elements and such come from, since they melt at high temperatures.
But water and the "stuff" that are gases at STP are volatile. So... what kept them "near" the earth while it was very hot (way past the boiling point of waster) and small and accreting? There wasn't enough of a magnetosphere to protect any atmosphere.
Could it be that H2O, N2 and O2 were created from the decomposition of very hot rocks?
Get up to date on planetary formation theory (Score:4, Interesting)
This is a rapidly evolving field and I don't pretend to have more than a very casual reader's knowledge - but think of it like this. The Earth is, in cosmic terms, a small planet. Its water layer is a minute fraction of its mass. In terms of the solar system as a whole, the percentage of the available water on Earth is extremely small.