Is Earth's Atmosphere an Import?

garg0yle writes "One of the questions about the formation of our planet is: where did the atmosphere come from? One theory is that the oxygen, nitrogen, and other gases were part of the coalescing ball, and 'seeped out' during the final stages of the planet's formation. However, a new article at Wired says isotopic analysis of krypton and xenon indicates that they (and the rest of our atmosphere) may be of extraterrestrial origin, either arriving via comets or being swept up from gas clouds."

Comments

Wha...?

[Anonymous Coward]

It's hard to understand how you can extrapolate a whole atmosphere's origins by looking at a couple of very rare gases like krypton and xenon.

Given that all the elements that make up the Earth were manufactured in the same solar furnace(s) why is it necessary that some originated separately from others? How do you then explain the huge atmospheres of the Gas Giants? It would take an unlikely number of very large asteroids to do the job.

This hypothesis suffers from the same shortcomings as the Transpermia idea. It just moves the problem elsewhere, at best.

Re:Wha...?

[Antique Geekmeister]

Oh, dear me. I can *see* the little propellers tied to your wrists helping you wave your hands.

In this case, the isotopic ratios are small fractions of the differences between the masses of different actual elements. The profound mass differences and related escape velocities of different gaseous _elements_ far overwhelms the differences in masses between the distinct isotopes: thus, any atomic weight related differences are nearly irrelevant. The possible exceptions are tritium and deuterium, which are respectively 3 and 2 times the mass of hydrogen atoms, but they're unstable enough that they're unlikely to come from ancient sources. Rather, they arise as byproducts of certain types of fission, especially tritium. In their cases, plain hydrogen ions or molecules can be lost to interplanetary or interstellar space relatively easily. Deuterium lasts, tritium has a half-life of 12.5 years, so it's long-gone.

But do _not_ confuse the "density of the nebula" with the mass or the atmosphere of Earth and other planets. I can see where that would be dominated by the overall mass of the nebula from which they formed, but the proximity of the planets to the Sun influences the elimination of atmospheric hydrogen and light chemicals by keeping the planets warmer and allowing them to lose their lighter chemicals to space.

Some Krypton isotopes are stable and thus more likely to reflect ancient conditions than tritium, for example. And refinement via normal, chemical means available on a planetary mass or its crust are unlikely to refine the isotopes, so it's reasonable to make some guesses about the original materials of the atmosphere's creation from the isotopic ratios.

Look at the science

[JadeBuddha23]

Vegetation on this planet has been here a huge amount of time. How much time? If all of human existence, in it's entirety, were a single pixel, the age of the earth would be nearly 6000 pixels long. Vegetation have been here for 1300 pixels. That's an awful long time for the plants (completely unencumbered by man) to create oxygen.

Re:Science?

[MightyMartian]

None of the planets you list have the proportionally large amounts of O2 that Earth does. It's not that Earth has a large atmosphere, it's that the atmosphere is in so many ways different from even the other Earth-like bodies (hint Venus and Mars' atmospheres are dominated by CO2). The gas giants are a totally different creature; they are largely made up of hydrogen.

Re:Science?

[TapeCutter]

Life is reponsible for the O2 we see today, it's the waste product of plants photosynthesisng CO2. It's not that farfetched to think we could terraform the venutian atmosphere to contain a lot more O2 by simply sprinkling airborne photosynthetic micro-oganisimis on it.

Re:Science?

[TapeCutter]

"Granted, if the time frame were to match that of what it took on earth, it would take a billion years or two."

Modern micro-organisims are many orders of magnitute more effcient at breeding and CO2 cracking than ancient stromatolites but yes it would still be a fairly slow process compared to a human life span.