Rosetta finds comet's water vapour to be significantly different from Earth's
esa.int
esa.int
Okay, a different isotope ratio in water from a comet as contrasted with water generally found on earth would indeed be a clue to how water might have traveled from one orbiting body to another early in the development of the solar system. This kind of isotype checking (for isotopes of other elements) is one of the things done to confirm that rocks found on earth are presumptively from other parts of the solar system.
DNA has a 'half-life' of ~500 years. Panspermania may still be a viable theory, but it is very restricted in terms of stellar distance/time in transit.
http://en.wikipedia.org/wiki/Standard_conditions_for_tempera...
> One of the leading hypotheses on Earth’s formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. But, today, two thirds of the surface is covered in water, so where did it come from?
Temperature is just an expression of mean kinetic energy of particles. If gases (especially light gases) are hot enough, their kinetic energy can correspond to a velocity that actually exceeds the escape velocity of Earth's gravitational well. This is how hot gases can be removed completely from the Earth's atmosphere (and then solar wind & radiation take care of removing it from there). Even at today's atmospheric temperatures, helium gas (molecular weight of 4 atomic mass units, much lighter than molecular oxygen, nitrogen, etc.) can escape from Earth's atmosphere.
(EDIT: actually, on second thought, N2 would have a higher molar weight than H2O...)
As far as methane, it seems to all mostly be biogenic[1].
[1] - http://www.astrobio.net/news-exclusive/methane-on-earth/
Isn't it possible that early Earth contained many times as much H2O as it does now (like some of those Jovian satellites that are covered in hundreds of miles of ice), and what we have now is simply what's left after the majority "boiled off"? That way, there would be no need for comets and asteroids to return the lost water to Earth.
Other comments in this thread mention vast amounts of water trapped deep inside the Earth, as well as outgassing of nitrogen after the Earth has cooled down. Perhaps the water near the surface of the early Earth did "boil off" entirely, but what we have now is the result of subsequent outgassing?
To address the first part of your question – The Big Bang (which happened 13.8 billion years ago) created ~only hydrogen and helium. So, no water existed in the early Universe (a) because there were no oxygen atoms formed in the Big Bang and (b) the early Universe was too hot to form water molecules even if oxygen was present.
>>> during Earth's creation?
Whether water was present on the Earth from "day one" of its formation (~5 billion years ago, much later than the Big Bang) is still an open question, but part of why it might be unlikely is that the Earth is close enough to the Sun that it was too hot for water to stay as ice or liquid on Earth's surface (before Earth's atmosphere formed). Water that forms in comets (further away from the Sun) doesn't have that problem, as comets would be in colder parts of the early Solar System.
http://en.wikipedia.org/wiki/Supernova_nucleosynthesis.
Nucleosynthesis says that at the end of the life of a star, heavier elemnts are formed as a byproduct.
http://en.wikipedia.org/wiki/Graphical_timeline_of_the_unive...
If you're interested in cosmology, there are a ton of fascinating popular science books on the topic, and research is very active and ongoing. As an introduction, I recommend Cosmos by Carl Sagan. It's a bit outdated these days, but the main points hold and it's a fascinating read from start to finish. Alternatively, if you prefer video, check out Cosmos: A Spacetime Odyssey with Neil deGrasse Tyson. It's an up-to-date retelling of Sagan's original idea.
There weren't any Oxygen atoms around until long after the big bang, and only a handful (in cosmic terms) of non-Hydrogen atoms.[1]
H2O molecules couldn't form until Oxygen had been synthesized, which occurs when a star exhausts its Hydrogen and begins fusing its Helium[2]. So water probably didn't exist until well into the the first or second generation of stars.
It's an interesting finding, but Jovian comets are one population of survivors. We have a lot more data to gather to fill out the most plausible picture of the early solar system and the likely source of terrestrial water.
Has there ever been an estimate made of the number of strikes needed to deliver the volume of water currently on Earth? I have to think it's enormous.
have a look at the image in this link:
>>A reservoir of water three times the volume of all the oceans has been discovered deep beneath the Earth's surface. The finding could help explain where Earth's seas came from.
http://www.newscientist.com/article/dn25723-massive-ocean-di...
Note: at extreme temps and pressures in the core, water as we know it is not a good guidepost. It may be crystallized or associating strongly with other exotic crystals and 'plastic'-y compounds at the Moho layer and other transition zones deep down. Also, just counting O and H elements is likely to not get you far there either. The story of how we got our oceans is FAR from complete. I'd wager we are in the 2nd page of the prologue though, which, for 60 years of real work, is pretty good compared to most fields.
1) http://adsabs.harvard.edu/full/1987A%26A...187..435E
How was it done this time?
Or else, what would have attracted the water away from the earth's atmosphere? And if so, why wouldn't it have attracted away the azote and oxygen and all of the atmosphere at the same time? Or was there not yet an atmosphere?
"One of the leading hypotheses on Earth’s formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. "
So where would it actually have boil to? I thought gravity affected water also in gas state. Just like the atmosphere doesn't "boil off", why would the water?
https://en.wikipedia.org/wiki/Atmospheric_escape
Essentially, because the distribution of thermal energy has a fairly long tail, it is possible for some lighter particles to reach escape velocity. The hotter the atmosphere, the more (and heavier) particles escape.
I don't know why you changed the title to something claiming a stronger result than their title: "ROSETTA FUELS DEBATE ON ORIGIN OF EARTH’S OCEANS". I'm not a planetary guy, but I think while the evidence is moving that way, the claim in your title is definitely premature.
Here's a distillation of their results (from their post) that seems far more in line with their claims than your title:
>“Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans.”
I see what you did there. :)
All we know is that this comet shows a different fraction of deuterium, compared to Earth, and some other comets we've checked are all different. So the jury is still out. We need more data, lots more.