
Billion-year-old air reveals surprise about oxygen on ancient Earth - miraj
http://www.cbc.ca/news/technology/ancient-air-oxygen-life-1.3698842
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rebelde
I see articles like this one every once in a while.

A chemistry professor once told my class that due to the rate of diffusion,
that we had just learned, the test of the "old air" would be wrong.

I don't know chemistry well. My question is if the salt completely stopped all
diffusion over the last billion years. Maybe somebody here can answer.

~~~
bduerst
If I remember correctly, NaCl atoms are packed pretty closely together in
crystallized form. They seem to be only looking at large crystalline
structures, which do not have evidence of disruption.

Of course, they also said they used the same method with modern salt, and the
O2 levels were lower than atmosphere by 9.2% for one of those samples.

It seems fairly legit but it would be great if they could test salt from the
same period but from a different mine.

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TimGremalm
"What they found may have implications for the origin of complex life.

The air, which has been preserved, undisturbed, in tiny pockets in the
crystals for about 815 million years, appears to contain 10.9 per cent oxygen
— just half the amount in the atmosphere today.

But it's about five times more than scientists expected for that time period,
which is about 200 million years before the first known multicellular
fossils."

~~~
Udo
_> 200 million years before the first known multicellular fossils_

This is a weird angle for the article to pursue. We have a monocellular fossil
record that dates back 4.1 billion years, and I don't think anyone is
proposing that we assumed up to this point oxygen levels took off _because_ of
multicellular life. A high oxygen level is probably one of many
_prerequisites_ for complex life, but that doesn't mean the genetic machinery
was available as soon as it reached a certain concentration.

~~~
omarchowdhury
Wouldn't oxygen producing organisms such as plants and trees be a cause for
oxygen levels taking off?

~~~
adrianratnapala
I thought even today phytoplankton produced more oxygen than all the
multicellular plants put together.

I might just be imagining that factoid though.

~~~
HCIdivision17
That was my understanding as well. The idea being that there is a _lot_ of
volume in the first few meters of ocean surface area churn. It's not hard to
imagine that does better in surface area than (even a lot) of plants.

~~~
ethbro
Not forgetting the fact that it seems like it would be substantially easier
for a faintly mobile fluid filled bag(s) of DNA to survive and reproduce in an
aqueous environment!

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dghughes
What I find so interesting is why is the oxygen on Earth 21% why not 5%.

I can understand why not 90% since it's so reactive but 21% seems so high.
Even more so now in modern times with seven billion people and billions of
other animals plus industrialization I'd expect atmospheric oxygen to be
falling rapidly.

We humans are pretty lucky to be able to breath, thank you ocean algae!
Honorable mention to trees, good job.

~~~
dmd
Just to give some scale here:

A human uses about 0.84 kilograms O2 per day. There is about 5e18 kg O2 in the
atmosphere.

Excluding all other sources of O2 consumption and replenishment, it would take
about 500000 years for the current population of humans to "use up" all the
current O2.

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keithwhor
Would be interesting to hear a discussion about how this impacts the timeline
of the Great Oxygenation Event [1], and where there's conflict with what's
proposed. If there's somebody a little more familiar with the geological
evidence it would be great to know a little more.

[1]
[https://en.m.wikipedia.org/wiki/Great_Oxygenation_Event](https://en.m.wikipedia.org/wiki/Great_Oxygenation_Event)

~~~
peter303
You are talking about seperated events, one 800 MY and other 2400 MY.

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IanDrake
Here's what worries me about this type of extrapolation:

"The researchers also compared salt samples from other halite deposits of
different ages — including the modern day — when oxygen concentrations were
known and found their results matched up with known concentrations. That gave
them confidence in their result, they said."

OK, so you take a recent sample and it matches up. Great.

But this seems to assume there is some sort of barrier at the atomic level
that "traps" the atmosphere at the time the salt crystals were formed and that
time and pressure will never have an impact on what components of the
atmosphere remain in the salt crystal.

~~~
zdkl
I don't know who downvotes this because parent does have a point: there are
extensive chemical transfers involved in the creation of minerals and
crystals, it's not obvious at all that the atmospheric bubbles where
chemically isolated from the encasing crystal afaict

~~~
maxerickson
I didn't down vote the above comment, but when the paper is available,
complaints should usually be about something specific in the paper, not hand
wavy concerns about methodology.

[http://geology.gsapubs.org/content/early/2016/07/08/G37937.1...](http://geology.gsapubs.org/content/early/2016/07/08/G37937.1.full.pdf)

The paper discusses the type of crystal they studied and how they formed (and
cites further work on those topics).

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adamkruszewski
But how do we know that those crystals were formed during "normal" conditions?
ie. why is it valid to interpolate the air structure for the whole "ancient
Earth"? I'm just curious how is it done?

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pvaldes
Dissolved oxygen in water decrease when temperature and salts increase. Sea
water have two hydrogen by each oxygen, and contains also atoms of sodium,
chloride, magnesium, sulphur, among other. Therefore, saltwater will not have
a 21% of oxygen normally, and a 10% of oxygen in salt should not be translated
as: "wow, in that time there was only the half of the current oxygen in the
air, how animals could live?". Aquatic organisms are adapted to the normal
rate of between 6 and 12 mg of dissolved oxygen for each L of saltwater.

On the other side, if saltwater becoming brine releases gradually its oxygen,
maybe the oxygen in an unknow mass X of water, could be trapped and slowly
accumulate in a bubble under tons of silt.

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Zenst
Nice to measure it but wasn't there already proof of larger amounts of oxygen
in the past and the earliest life (one of from what we know) was a bacteria
that produced the first oxygen in abundance and explains the higher levels and
is indeed thought why, or least factor in why early mammals were larger and
during the dinosaur days (sorry but easier to call it that for many) the
oxygen levels were higher than today by far.

Nice article to matchup with this
[http://www.scientificamerican.com/article/timeline-of-
photos...](http://www.scientificamerican.com/article/timeline-of-
photosynthesis-on-earth/)

~~~
smhenderson
Well this is talking about 200,000 years before the explosive emergence of
life on Earth. Before this discovery it was thought that there was much less
oxygen at that time (the Neoproterozoic era according to the article). And
that life had to wait until more oxygen came along before it could happen. Now
they are basically saying the oldest fossils we have found are probably not
the oldest we could find. Time to look for older signs of life!

~~~
_kst_
I think you mean 200 million, not 200 thousand.

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misiti3780
Does this affect any of the conclusions in Nick Lane's books (for anyone here
that has read them)? (It seems like it doesnt to me)

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known
Earth is ~4 billion years old

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smcg
So... how did it smell?

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philbarr
It couldn't. It had no nose...

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northisup
Click bait headline.

