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Fraser
2005-Apr-19, 05:37 PM
SUMMARY: The biggest mass extinction in the Earth's history happened approximately 250 million years ago. During the "Great Dying", more than 90% of creatures in the ocean, and 75% of life on land went extinct. What caused the extinction is still up for debate, but a researcher from the University of Washington thinks that low levels of oxygen in the atmosphere sure didn't help. Oxygen went down to 12% (currently it's 21%), and this made standing at sea level the same as being atop a 5,300 metre mountain (17,000 feet).

View full article (http://www.universetoday.com/am/publish/low_oxygen_great_dying.html)

What do you think about this story? Post your comments below.

Jeff
2005-Apr-19, 07:43 PM
I guess the next logical question is WHY did Oxygen levels drop?

lswinford
2005-Apr-19, 07:51 PM
Wow! So where was the oxygen? In carbon dioxide from animal expiration and dead plant decay? In additional water from the release of hydrogen compounds from the organic matter decompositions that we now recognize as coal, oil, and natural gas? In soil rusts as the water of heavy rains catalyze the oxidation of iron in the soil? In approximately the same physical quantities today but in different proportions because other gasses (from volcanic activity perhaps) predominated (maybe there was more nitrogen, maybe hydrocarbon gasses were more prevalent and later broke up, perhaps by the solar energy disassociation that happens in the higher reaches of the atmosphere)? Maybe we lost a lot of the atmosphere (ala Mars) and of what later remained oxygen was in differing proportion? Tantalizing piece of the puzzle that needs more data, a broader picture.

TuTone
2005-Apr-19, 08:51 PM
How did the oxygen level drops and how did they rise again?

qraal
2005-Apr-20, 12:50 AM
Hi All

Oxygen imbalances can come about from previously oxygen-free minerals being exposed and reacting with oxygen in the air. Biological productivity can also be a big net sink if too much old biological carbon is being exposed for consumption in the oceans so creatures can use it and form carbon dioxide again. Or, as someone has mentioned, volcanic gases like hydrogen, methane and sulphur can use up the oxygen too. Perhaps a lot of CO2 and SO2 was being sunk in the oceans steadily robbing the air. The volcanism at the end of Permian upset the sequstered gases and caused sporadic and highly deadly gas releases over the hundred thousand or so years of the Great Dying.

The big oxygen spike prior to this Big Gasp could have come from more biological material being buried than exposed to be turned back into carbon dioxide. Since the big coal forests were growing and undergoing burial in the preceeding Carboniferous that makes sense. All these processes have been suggested prior so I'm not being original.

qraal

daddy
2005-Apr-20, 01:45 AM
It would be horrible to think that a universal flood wiped out all oxygen producing plants in pangea and that the earth was pummelled with asteroids at the same time to help deplete o2 levels by all that nasty volcanic stuff happening.
badbuckbuckbreaker

sam_lelime
2005-Apr-20, 02:52 AM
Obviously there where several factors, today human civilaisation in the source of and the controller of many of these factors.... good to see some nations following through with the Kyoto reform... hopefully the rest will come to the party.

Eric Vaxxine
2005-Apr-20, 12:54 PM
...and what kind of O2 trend are we on? How is this balance maintained? By luck?

I overheard somewhere that it is possible that the dinosaurs grew so BIG was because more oxygen was available than is present today.

qraal
2005-Apr-20, 11:24 PM
Hi Eric

The trend is hard to gauge. Currently an increase is indicated by some researchers, but it's a slow, slow rise.

Some have predicted disaster when the O2 levels hit 23.5% because they think all the forests will burn down based on some old experiments that measured burning in O2 rich atmospheres. We now know that the original experiment used paper as its plant analogue and this is actually horribly wrong. Plants don't erupt in flames due to sparks even at high oxygen levels, unlike paper, so that particular disaster has been ruled out.

The various gases are controlled by biology and geology - different oxygen using processes soak up any excess. Likewise carbon dioxide and even nitrogen is ultimately cycled through life/geology. Carbon dioxide will be the crucial factor in a billion years time because the rise in average temperature as the Sun brightens will cause more of it to be lost to geology and eventually life on land will be unable to survive. Plants need CO2 - photosynthesis makes it into sugars. C4 (mostly trees) photosynthesis needs higher levels than C3 (mostly grasses), but eventually it will drop below even C3 levels. Ocean life gets carbon from geology as well as atmosphere and can tolerate lower levels.

qraal

qraal
2005-Apr-20, 11:30 PM
BTW dinosaurs evolved during the low-oxygen era of the Triassic and probably developed their unique pneumatic-sac supplementary breathing system to compensate for the low O2. Some species got big long before O2 levels rose significantly in the later Jurassic and Cretaceous, so there's not much going for the theory they grew big on high O2.

And if you're wondering if dinos are just big lizards centuries old - that's another fringe idea - it's a load of coswallop. Dinosaur bones contain annual growth rings just like other diapsid amniotes (commonly, and incorrectly, called reptiles) and the rings indicate that dinos grew BIG in just a few years. Adult sauropods might have lived centuries, but their growth took only a decade or so.

starlight
2005-Apr-21, 09:00 AM
Originally posted by TuTone@Apr 19 2005, 08:51 PM
How did the oxygen level drops and how did they rise again?
I've been away for a while and only just read this article but my first thought was that the sunlight had been gone and photosynthesis levels dropped in consequence:

One of the theories for the great extinction involves some sort of crash from an alien body. This would have projected a lot of debris that could have been floating in the atmosphere, blocking the sun, reducing the photosynthesis and consequently the oxygen levels...

but this is just a thought :blink:

lswinford
2005-Apr-25, 01:46 PM
Graal, I follow you, but couldn't help a chuckle when you remarked "Plants don't erupt in flames due to sparks even at high oxygen levels, unlike paper, so that particular disaster has been ruled out."

Now adays they call those "sparks" lightning and the results forest fires. :lol:

shery
2005-Apr-26, 10:20 PM
holla iam doing a reserach on the Planets Neptunes and i need help on finding what neptunes mantle is made of... ;)

antoniseb
2005-Apr-26, 10:47 PM
Originally posted by shery@Apr 26 2005, 10:20 PM
I am doing a reserach on the Planet Neptune and I need help on finding what Neptune's mantle is made of.
We can only guess as to whether it even HAS a mantle, let alone what, if anything it is made of. What we see on Neptune is the top of a VERY deep atmosphere. Perhaps under there is some combination of ices.

TuTone
2005-Apr-27, 01:45 AM
Originally posted by pauloaguia+Apr 21 2005, 09:00 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (pauloaguia @ Apr 21 2005, 09:00 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-TuTone@Apr 19 2005, 08:51 PM
How did the oxygen level drops and how did they rise again?
I&#39;ve been away for a while and only just read this article but my first thought was that the sunlight had been gone and photosynthesis levels dropped in consequence:

One of the theories for the great extinction involves some sort of crash from an alien body. This would have projected a lot of debris that could have been floating in the atmosphere, blocking the sun, reducing the photosynthesis and consequently the oxygen levels...

but this is just a thought :blink: [/b][/quote]
I heard about that in a movie once....I believe it was Deep Impact.

GOURDHEAD
2005-Apr-27, 01:35 PM
Perhaps under there is some combination of ices. Probably of silicon, iron and such and even they may be a bit mushy.

lswinford
2005-Apr-27, 09:00 PM
Sherry, this may help

Jupiter probably has a core of rocky material amounting to something like 10 to 15 Earth-masses.

Above the core lies the main bulk of the planet in the form of liquid metallic hydrogen. This exotic form of the most common of elements is possible only at pressures exceeding 4 million bars, as is the case in the interior of Jupiter (and Saturn). Liquid metallic hydrogen consists of ionized protons and electrons (like the interior of the Sun but at a far lower temperature). At the temperature and pressure of Jupiter&#39;s interior hydrogen is a liquid, not a gas. It is an electrical conductor and the source of Jupiter&#39;s magnetic field. This layer probably also contains some helium and traces of various "ices".

The outermost layer is composed primarily of ordinary molecular hydrogen and helium which is liquid in the interior and gaseous further out. The atmosphere we see is just the very top of this deep layer. Water, carbon dioxide, methane and other simple molecules are also present in tiny amounts.

Recent experiments have shown that hydrogen does not change phase suddenly. Therefore the interiors of the jovian planets probably have indistinct boundaries between their various interior layers.

As it relates to Jupiter, a better observed gas giant. You can find the link at http://www.seds.org/nineplanets/nineplanet...ts/jupiter.html (http://www.seds.org/nineplanets/nineplanets/jupiter.html)

The URL for Neptune is http://www.seds.org/nineplanets/nineplanet...ts/neptune.html (http://www.seds.org/nineplanets/nineplanets/neptune.html)

Their estimate, however, is saying
Neptune&#39;s composition is probably similar to Uranus&#39;: various "ices" and rock with about 15% hydrogen and a little helium. Like Uranus, but unlike Jupiter and Saturn, it may not have a distinct internal layering but rather to be more or less uniform in composition. But there is most likely a small core (about the mass of the Earth) of rocky material. Its atmosphere is mostly hydrogen and helium with a small amount of methane.

Like Antonisub noted, we don&#39;t really know, but there are guesses out there from people qualified to make good guesses. Good luck on your study.