Minimum mass of habitable planet
Crown-Horned Snorkack
Mars is not habitable now (7 mbar atmosphere) but once upon a time
Mars had flowing rivers, steady dendritic drainage and occasional
outburst floods.
What was the atmospheric pressure on Mars back then?
How much more massive than Mars would a planet have to be to keep
atmosphere breathable for people? Assuming that the planet is also
warmer than Mars, in Earth´s orbit more vulnerable to atmospheric
escape?
Does this depend on what is defined as "breathable"?
It is alleged that Venus and Mars have less atmospheric escape because
they have cold exosphere, and exosphere is cold because carbon dioxide
radiates heat. Whereas nitrogen and oxygen exosphere of Earth (just
0,03 % carbon dioxide) tends to heat and escape.
Carbon dioxide is poisonous.
However, the Earth´s 0,3 mbar is far less than the poisonous amount to
people. People have 50 mbar carbon dioxide in lungs. In submarines,
there is normally 10 to 20 mbar carbon dioxide, which is perceivable
but quite tolerable.
People have no need for nitrogen. As for oxygen, people are adapted to
210 mbar, but they can do with 100 mbar under stress, and 150 mbar
comfortably.
Suppose that there were a planet with total of 165 mbar surface
pressure - 15 mbar carbon dioxide, 150 mbar oxygen, little nitrogen. 9
% carbon dioxide mixing ratio.
Can (unmodified) people breathe it comfortably?
Would the exosphere with 9 % carbon dioxide get hot in sunlight?
What would be minimum escape speed to keep the same atmosphere?
Now, the density of the planet/body has options. Moon has low density.
Mercury is very dense - denser than uncompressed Earth or Venus.
For a given escape speed, the lowest total mass would be small but
high density planet. A planet with the escape speed higher than that
of Mars would be heavier and bigger than Mercury - but it could be
denser (if it is bigger, it would be more compressed). You could
nevertheless have a planet which is smaller and denser than Mars.
So, what would be the minimum mass of habitable planet?
Androcles
"Crown-Horned Snorkack" <chorned...@hush.ai> wrote in message
news:73c10a24-c4ee-474b...@m36g2000hse.googlegroups.com...
Carbon dioxide is poisonous.
========================
Earth was not "habitable" for its first 3,000,000,000 years,
although it did support bacteria which changed the atmosphere
from CO2 rich to oxygen rich.
Mass is the least of your problems in being "habitable", but as
as minimum it should high enough to retain an atmosphere.
--
This message is brought to you by Androcles
http://www.androcles01.pwp.blueyonder.co.uk/
Robert J. Kolker
>
> How much more massive than Mars would a planet have to be to keep
> atmosphere breathable for people? Assuming that the planet is also
> warmer than Mars, in Earth´s orbit more vulnerable to atmospheric
> escape?
In addition to being massive, Mars would need a magnetic field.
Bob Kolker
Crown-Horned Snorkack
a massive atmosphere.
How much less massive than Venus would a nonmagnetic planet need to be
to lose atmosphere?
MWill...@gmail.com
wrote:
>
> So, what would be the minimum mass of habitable planet?
Titan manages a 1.5 bar pressure despite being smaller than Mars.
Granted, it's cold.
Can you even have a pure oxygen atmosphere without anything else?
Don't plants need to convert atmosphere to oxygen?
Bernard Peek
<14850294-86ae-4d97...@p25g2000pri.googlegroups.com>,
MWill...@gmail.com writes
Oxygen gas is so reactive that it's unlikely to be found free except
where there is a process that continually generates it.
--
Bernard Peek
London, UK. DBA, Manager, Trainer & Author.
Anthony Buckland
<MWill...@gmail.com> wrote in message
news:14850294-86ae-4d97...@p25g2000pri.googlegroups.com...
> ...
> Can you even have a pure oxygen atmosphere without anything else?
It turned out to be a really bad idea in the Apollo capsule fire.
A pure oxygen atmosphere has a boundless enthusiasm for
oxidizing, really rapidly, anything vaguely burnable given a
start.
pete...@gmail.com
<anthonybucklandnos...@telus.net> wrote:
> <MWillMar...@gmail.com> wrote in message
The fact that the capsule while sitting on the pad was held
at 1 full atmosphere was also part of the problem. I'm under
the impression that in flight, the pressure was considerably
reduced. I suspect this would also reduce the firehazard.
pt
pete...@gmail.com
The magnetic field reduces the solar radiation flux in the
upper atmosphere. In the case of Mars, the lack of a
magnetic field is thought to have allowed the radiation
to dissociate water molecules. The hydrogen escaped
into space, and the oxygen reacted with iron in the soil.
Thus, Mars dried out.
One factor you haven't mentioned is how *long* it has to
be habitable - billions of years? A few decades? If you
dumped enough oxygen on the Moon, you could create
a breathable atmosphere, but it would dissipate after
a while. I don't know what the duration would be, but
I'm under the impression it might take a few years or
decades to lose half the oxygen.
pt
Brian Davis
>> In addition to being massive, Mars would need a magnetic field.
>
> The magnetic field reduces the solar radiation flux in the
> upper atmosphere.
No. Photons are most certainly non-magnetic :)
> In the case of Mars, the lack of a magnetic field is thought
> to have allowed the radiation to dissociate water molecules.
Um, again, planetary magnetic fields actually have zero effect on
solar radiation. Charged particles, yes, but water is disassociated by
solar UV.
In fact, the only point I can think of in favor of a magnetic field is
to possibly prevent atmospheric stripping by the solar wind over time
(one factor thought to contribute to Mars' low surface pressure).
Venus maintains an atmosphere just fine without it, as would Earth,
and those atmospheres are nicely thick from the standpoint of
radiation shielding as well (in other words, you again don't need a
planetary magnetic field).
> One factor you haven't mentioned is how *long* it has to
> be habitable - billions of years? A few decades? If you
> dumped enough oxygen on the Moon, you could create
> a breathable atmosphere, but it would dissipate after
> a while. I don't know what the duration would be
Estimates are a few million years to ten million or so - plenty long
enough to be comfortably habitable, just not enough for natural
evolution. I'd agree, timescale is a critical assumption here, one
that's not really stated. I also have to assume that by "habitable",
the poster was postulating a shirtsleeve-for-unmodified-humans sort of
situation (as opposed to habitable = ability to support liquid water).
--
Brian Davis
Brian Davis
> Oxygen gas is so reactive that it's unlikely to be found free except
> where there is a process that continually generates it.
There are others ways of producing oxygen besides biology - like
having global oceans (or even ice - think Europa), and UV-
disassociating the water leaving O2 as the H escapes. The trick is not
to have a copious source of O2, but to have matched source and sink
rates. Put all your reduced material deep under an ocean, or an ice
sheet, and you can build up significant O2... but this probably isn't
"habitable" in the sense the poster wanted either.
> Can you even have a pure oxygen atmosphere without anything else?
Well... I suspect it's unlikely, but I can't think of a reason why
it's not possible. For terrestrial life there would be some issues -
you need at least a certain (trace) level of CO2 for terrestrial
plants (at 150 ppm at 1 Atm C3 plants are really at a standstill, so
lower than this all you'd have is C4's or maybe CAM-based
photosynthesis), but it's really trace. A bigger issue that I don't
know the limits on is N2 fixation - this is rather flaky & delicate
now (with 0.78 Atm of N2 handy, and only 0.2 Atm O2), and I've no idea
how low you can go on pN2 before nitrogen fixation essentially stops.
And that's a rather hard limit for an unassisted terrestrial biosphere
to cross.
--
Brian Davis
David Johnson
c4ee-474b-9ac...@m36g2000hse.googlegroups.com:
> However, the Earthïs 0,3 mbar is far less than the poisonous amount to
> people. People have 50 mbar carbon dioxide in lungs. In submarines,
> there is normally 10 to 20 mbar carbon dioxide, which is perceivable
> but quite tolerable.
>
> People have no need for nitrogen.
Well, actually, yeah, they do. Without nitrogen (fixed as nitrates)
plants don't grow. Which means no oxygen, no biosphere, no people. So
it's kinda important. Oh, you can suppose an ecosystem that _doesn't_ use
nitrogen - but then its chance that it's produced a "breathable"
atmosphere for people is very, very small.
> As for oxygen, people are adapted to 210 mbar, but they can do with 100
> mbar under stress, and 150 mbar comfortably.
So "comfortable" is a good 75% of current levels.
The O2 level's been higher in the past too. As high as 35% of the
atmosphere - or a good 165% of current levels. That tends to be hard on
plants if some sort of flame is introduced, however.
A pure (or nearly pure) oxygen atmosphere is probably impossible, if for
no other reason than how would you get _rid_ of all the other gasses?
Even Mars, whose gravity is so low only CO2 is heavy enough to really
hang around, still has 2.7% nitrogen in its atmosphere. Venus's is only
3.5%...but given Venus's pressure, that's still a _lot_ of nitrogen.
Standard answer given is that the planet's gravity has to be more than
Mars, but less than Earth to hang onto a (human viable pressure)
atmosphere - though exactly _how_ much more/less is also dependent on
other factors (where in the Solar system it is, etc.).
On the whole, I'd plonk for roughly half a G as a good minimum break
point.
David
--
_______________________________________________________________________
David Johnson home.earthlink.net/~trolleyfan
"So many of you come time and time again to watch this final end of
everything which I think is really wonderful and then to return home to
your own eras and raise families and strive for new and better societies
and fight terrible wars for what you know is right, it gives one real
hope for the whole future of lifekind...
...Except of course we know it hasn't got one."
David Johnson
0f6e-409b-a77...@z72g2000hsb.googlegroups.com:
> On 15 mai, 13:11, "Robert J. Kolker" <bobkol...@comcast.net> wrote:
>> Crown-Horned Snorkack wrote:
>>
>> > How much more massive than Mars would a planet have to be to keep
>> > atmosphere breathable for people? Assuming that the planet is also
>> > warmer than Mars, in Earth愀 orbit more vulnerable to atmospheric
>> > escape?
>>
>> In addition to being massive, Mars would need a magnetic field.
>>
> Mercury has magnetic field. Venus has none, but nevertheless possesses
> a massive atmosphere.
>
> How much less massive than Venus would a nonmagnetic planet need to be
> to lose atmosphere?
I'm not sure that is actually much of a factor unless you're really close
to the Sun. At Mercury distance, I _think_ having a magnetic field would
slightly slow down atmosphere loss, but I'm not sure.
IAE, even Venus _is_ losing atmosphere (very, very slowly) as is Earth so
"smaller than a Sun"* would be your cut-off point.
David
* And only then because - as a Sun - it's no longer a planet, magnetic or
otherwise.
Crown-Horned Snorkack
> On May 15, 1:33 pm, petert...@gmail.com wrote:
>
>
> > One factor you haven't mentioned is how *long* it has to
> > be habitable - billions of years?
> > A few decades?
Earth has been habitable a few hundred millions of years and it is not
known how long it shall be habitable. I think a few tens of millions
of years is enough to consider a planet as habitable because this is
the time it would take to evolve from uninhabitable through almost
habitable to barely habitable.
> > If you
> > dumped enough oxygen on the Moon, you could create
> > a breathable atmosphere, but it would dissipate after
> > a while. I don't know what the duration would be
>
> Estimates are a few million years to ten million or so - plenty long
> enough to be comfortably habitable, just not enough for natural
> evolution. I'd agree, timescale is a critical assumption here, one
> that's not really stated. I also have to assume that by "habitable",
> the poster was postulating a shirtsleeve-for-unmodified-humans sort of
> situation (as opposed to habitable = ability to support liquid water).
>
Ability to support liquid water (and plants, algae or both) is
necessary but not sufficient. Shirtsleeve environment is not required
(a situation where unmodified humans better wear a raincoat is still
habitable). But what is the essential part is that unmodified humans
should not need masks (And that, for example, rules out all planets
with more than 3000...5000 mbar nitrogen, irrespective of climate or
biosphere - even if native animals are perfectly adapted, humans are
too crippled by nitrogen narcosis).
Robert J. Kolker
>
>
> Earth has been habitable a few hundred millions of years and it is not
> known how long it shall be habitable. I think a few tens of millions
> of years is enough to consider a planet as habitable because this is
> the time it would take to evolve from uninhabitable through almost
> habitable to barely habitable.
Life originated on earth about 3.5 billion years ago. So it has been
habitable by something living for that long.
The Archea, the predicessors to the cyano bacterium go back over 2.5
billion years.
Bob Kolker
Harri Tavaila
4a2447...@y21g2000hsf.googlegroups.com:
> On May 15, 6:11 am, "Robert J. Kolker" <bobkol...@comcast.net> wrote:
>> Crown-Horned Snorkack wrote:
>>
>> > How much more massive than Mars would a planet have to be to keep
>> > atmosphere breathable for people? Assuming that the planet is also
>> > warmer than Mars, in Earth´s orbit more vulnerable to atmospheric
>> > escape?
>>
>> In addition to being massive, Mars would need a magnetic field.
-clip-
> One factor you haven't mentioned is how *long* it has to
> be habitable - billions of years? A few decades? If you
> dumped enough oxygen on the Moon, you could create
> a breathable atmosphere, but it would dissipate after
> a while. I don't know what the duration would be, but
> I'm under the impression it might take a few years or
> decades to lose half the oxygen.
I believe it would take something in the order of millennia - though
this figure is based on a vague recollection on a book I once read.
H Tavaila
Michael G. Koerner
> Crown-Horned Snorkack <chorned...@hush.ai> wrote in news:a39a03c6-
> 0f6e-409b-a77...@z72g2000hsb.googlegroups.com:
>
>> On 15 mai, 13:11, "Robert J. Kolker" <bobkol...@comcast.net> wrote:
>>> Crown-Horned Snorkack wrote:
>>>
>>>> How much more massive than Mars would a planet have to be to keep
>>>> atmosphere breathable for people? Assuming that the planet is also
>>>> escape?
>>> In addition to being massive, Mars would need a magnetic field.
>>>
>> Mercury has magnetic field. Venus has none, but nevertheless possesses
>> a massive atmosphere.
>>
>> How much less massive than Venus would a nonmagnetic planet need to be
>> to lose atmosphere?
>
> I'm not sure that is actually much of a factor unless you're really close
> to the Sun. At Mercury distance, I _think_ having a magnetic field would
> slightly slow down atmosphere loss, but I'm not sure.
>
> IAE, even Venus _is_ losing atmosphere (very, very slowly) as is Earth so
> "smaller than a Sun"* would be your cut-off point.
Both are losing atmosphere, but it both cases it is at an equilibrium with
replenishment through volcanic activity.
Also, as for a magnetic field, it also protects the inhabitants from cosmic
radiation, something that would be fatal to life without it.
--
___________________________________________ ____ _______________
Regards, | |\ ____
| | | | |\
Michael G. Koerner May they | | | | | | rise again!
Appleton, Wisconsin USA | | | | | |
___________________________________________ | | | | | | _______________
Martin Brown
> David Johnson wrote:
>> Crown-Horned Snorkack <chorned...@hush.ai> wrote in news:a39a03c6-
>> 0f6e-409b-a77...@z72g2000hsb.googlegroups.com:
>>
>>> On 15 mai, 13:11, "Robert J. Kolker" <bobkol...@comcast.net> wrote:
>>>> Crown-Horned Snorkack wrote:
>>>>
>>>>> How much more massive than Mars would a planet have to be to keep
>>>>> atmosphere breathable for people? Assuming that the planet is also
>>>>> escape?
>>>> In addition to being massive, Mars would need a magnetic field.
>>>>
>>> Mercury has magnetic field. Venus has none, but nevertheless possesses
>>> a massive atmosphere.
>>>
>>> How much less massive than Venus would a nonmagnetic planet need to be
>>> to lose atmosphere?
>>
>> I'm not sure that is actually much of a factor unless you're really
>> close to the Sun. At Mercury distance, I _think_ having a magnetic
>> field would slightly slow down atmosphere loss, but I'm not sure.
>>
>> IAE, even Venus _is_ losing atmosphere (very, very slowly) as is Earth
>> so "smaller than a Sun"* would be your cut-off point.
>
> Both are losing atmosphere, but it both cases it is at an equilibrium
> with replenishment through volcanic activity.
And it is the lighter components for the most part escaping.
>
> Also, as for a magnetic field, it also protects the inhabitants from
> cosmic radiation, something that would be fatal to life without it.
>
Not sure the magnetic field is all that critical. The atmosphere already
provides a reasonable amount of protection from most solar storm charged
particles. In density terms roughly equivalent I suppose to 32 foot of
water. Mutation rates would be higher with no magnetic field.
Having a magnetic field provides the inhabitants with nice displays near
the poles.
Regards,
Martin Brown
** Posted from http://www.teranews.com **
Dimensional Traveler
> What is the minimum mass of a habitable planet?
>
--
.-- - ..-. ..--..
Crown-Horned Snorkack
> Crown-Horned Snorkack wrote:
>
> > Earth has been habitable a few hundred millions of years and it is not
> > known how long it shall be habitable. I think a few tens of millions
> > of years is enough to consider a planet as habitable because this is
> > the time it would take to evolve from uninhabitable through almost
> > habitable to barely habitable.
>
> Life originated on earth about 3.5 billion years ago. So it has been
> habitable by something living for that long.
>
Late archean Earth (a bit more than 2,5 milliards of years ago) had
rivers which abraded pyrite and uraninite into rounded pebbles and did
not oxidize them. Thus, no oxygen in air. Not inhabitable for people!
don findlay
Crown-Horned Snorkack wrote:
> On 16 mai, 00:36, "Robert J. Kolker" <bobkol...@comcast.net> wrote:
> > Crown-Horned Snorkack wrote:
> >
> > > Earth has been habitable a few hundred millions of years and it is not
> > > known how long it shall be habitable. I think a few tens of millions
> > > of years is enough to consider a planet as habitable because this is
> > > the time it would take to evolve from uninhabitable through almost
> > > habitable to barely habitable.
> >
> > Life originated on earth about 3.5 billion years ago. So it has been
> > habitable by something living for that long.
> >
> But not by people.
"Stromatolites for dinner, anyone?" asked Alice?
"Yum, ..." Replied the gryphon,
"You mean soup?" sobbed the Mock Turtle
"No," said Alice, clouting him round the lughole with the ladle she
held in her hand. "I meant exactly what I said, not whatever you take
it to mean. I said 'straw', 'mat', 'o'lights'. Where on Earth were
you brought up, to think that when a person says something, they mean
exactly the opposite of what they clearly enunciate?"
Crown-Horned Snorkack
oxygen, did the extra oxygen interfere with nitrogen fixation?
Robert J. Kolker
> What is the minimum mass of a habitable planet?
Habitable for what or for whom?
If a planet could retain water and a methane atmosphere for a half
billion years it could cook of Archae or the chemical replicators thereto.
Bob Kolker
Remus
wrote:
> So, what would be the minimum mass of habitable planet?
I've not directly seen any calculations showing
exactly how long it would take and atmosphere
derived from comets to bleed away from the
Moon. I am also not sure how quickly the
geology of the moon would react to some
type of atmosphere or water and lock up
water or carbon dioxide into the crust as
hydrates or carbonates if one were to bombard
it with a small ice moon or an array of
comets. Probably one of the most
major difficulties involved with terraforming
the moon could have to do with side effects
from its rotation period with respect to the sun.
Anyway, I think that the standard reason
why Mars has as thin of an atmosphere
as it does is not because it can not
retain a thicker atmosphere, but because
vulcanism is required to convert carbonates
in the crust of Mars or Earth and convert
it back to carbon dioxide in the atmosphere.
A vast amount of Earth's carbon is locked
up in the Earth's crust in carbonate rocks,
a small amount of it is in Earth's life, leaving
only trace amounts of CO2 left in the Earth's
atmosphere. The atmosphere of Mars has
a greater partial pressure of CO2 than the
atmosphere of Earth does. Water on Earth
helps to condense the CO2 on Earth into
carbonate rocks, and that CO2 is then
liberated back into the atmosphere
from volcanism.
Because, Mars has a lower level of
volcanism than Earth does, however,
residual water from a long time ago
allowed much of Mars's CO2 to
be locked into carbonate rocks. It
stayed there because the lack of
volcanoes kept it from being cycled
back into the atmosphere again.
It might be that an Earth like atmosphere
is therefore not limited by the planet's
ability to hold on to an atmosphere, however,
but rather its ability to retain volcanism
so that it might continue to cycle potential
gaseous material between the crust and
the atmosphere.
Venus, however, lost its ability to retain
hydrogen because it was close enough
to the sun for water to be wafted high
enough for UV light to split the hydrogen
from the oxygen in water and then dissipate
the hydrogen in water into space. Volcanism
kept the CO2 out of rocks, and the net result
is a CO2 atmosphere on the order of a hundred
times more dense than the earth's atmosphere,
one that approaches the density of a liquid.
If all of the CO2 that were in Earth's carbonate
rocks were released into the atmosphere,
the Earth's atmosphere would be very similar
to that of Venus. Indeed, the Sun is heating up.
Supposedly in only about a billion years from
now the Sun will become hot enough to start
dissociating hydrogen from water vapor in the
upper atmosphere of Earth, gradually making
it lose all of its water. Then volcanism will
have its way with Earth's carbonates, and
Earth will become a planet very much like
Venus.
Supposedly there are supposed to be about
5 or 6 billion more years after that when the
Sun will remain on the main sequence, then
for about 500 to 700 million years the
Sun will go through various short lived phases
as it passes through the different Giant star
types. A lot of people are not entirely sure
if the Earth will be swallowed up by the Sun
during one of these giant star phases or
whether the Earth will just barely survive.
Then the Sun will shed a lot of its gas into
space leaving a carbon core called a white
dwarf. The tiny but dense and dimmer
stellar remnant will then take literally
billions of years to cool.
Anyway, more than a billion years into
the future, Earth itself will need to be
terraformed to enable it to continue to
support life. Over one and a half billion
years ago also, the Earth's atmosphere
had negligible amounts of free oxygen
and thus would not sustain the type
of animals that exist upon it today.
Depending on the relative age that
you would want the planet to retain
a specific type of atmosphere with
water, you would probably want
to factor in to what extent the planet
would retain volcanism.
Of course, if you have a B or A main
sequence star as your source of light,
the star isn't going to live longer than
a billion years before it goes supernova,
and so the semi-habitable planet is
still going to be subject to impacts
from other objects or planetesimals
in the primordial nebula or ring even
if it does have an atmosphere.
If you have an M class main sequence
star, however, it is going to be so dim
that the planet will have to be very close
to the star to get enough starlight to melt
water ice. Tidal effects at that distance
would lock the planet into always showing
the same face to the star, which in theory
could also have effects on its climactic
conditions at various points on the planet's
surface.
Brian Davis
wrote:
> Back in Carboniferous, when the atmosphere had something like 0,4 atm
> oxygen, did the extra oxygen interfere with nitrogen fixation?
I don't know. But given how oxygen-intolerant the current mechanism
is, it might have been a tougher proposition. I was more concerned
with what the minimum pN2 is that nitrogen-fixation requires... and I
really have no idea.
--
Brian Davis
Crown-Horned Snorkack
> On May 14, 11:22 pm, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> wrote:
>
> > So, what would be the minimum mass of habitable planet?
>
> I've not directly seen any calculations showing
> exactly how long it would take and atmosphere
> derived from comets to bleed away from the
> Moon. I am also not sure how quickly the
> geology of the moon would react to some
> type of atmosphere or water and lock up
> water or carbon dioxide into the crust as
> hydrates or carbonates if one were to bombard
> it with a small ice moon or an array of
> comets. Probably one of the most
> major difficulties involved with terraforming
> the moon could have to do with side effects
> from its rotation period with respect to the sun.
>
> Anyway, I think that the standard reason
> why Mars has as thin of an atmosphere
> as it does is not because it can not
> retain a thicker atmosphere, but because
> vulcanism is required to convert carbonates
> in the crust of Mars or Earth and convert
> it back to carbon dioxide in the atmosphere.
>
The other atmospheres have Earth 800 mbar, Titan 1500 mbar, Venus 3200
mbar. Why those particular numbers?
pyotr filipivich
MWill...@gmail.com wrote on Thu, 15 May 2008 08:59:51 -0700 (PDT)
in soc.history.what-if :
>On May 14, 11:22 pm, Crown-Horned Snorkack <chornedsnork...@hush.ai>
>wrote:
>
>>
>> So, what would be the minimum mass of habitable planet?
>
>Titan manages a 1.5 bar pressure despite being smaller than Mars.
>Granted, it's cold.
>
>Can you even have a pure oxygen atmosphere without anything else?
A pure Oxygen atmosphere will not last a long time, due to the
reaction of oxygen with anything it can. I recall reading that if the
atmosphere were to go over 25% oxygen (up from the current 20%) there
would be a major increase in the number and severity of wild fires.
>Don't plants need to convert atmosphere to oxygen?
Plants, by and large, "breathe" carbon dioxide, and "pee" oxygen,
polluting their environment. Animals do the reverse: breathe oxygen,
and pollute their environment with carbon dioxide.
--
pyotr filipivich
Most of the intelligentsia haven't studied history, so much
as they've absorbed the Correct Position on "History".
Crown-Horned Snorkack
> [Default] I missed the Staff meeting, but the Memos showed that
> in soc.history.what-if :
>
> >On May 14, 11:22 pm, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> >wrote:
>
> >> So, what would be the minimum mass of habitable planet?
>
> >Titan manages a 1.5 bar pressure despite being smaller than Mars.
> >Granted, it's cold.
>
> >Can you even have a pure oxygen atmosphere without anything else?
>
> A pure Oxygen atmosphere will not last a long time, due to the
> reaction of oxygen with anything it can.
Anything it can, but it cannot react with everything.
> I recall reading that if the
> atmosphere were to go over 25% oxygen (up from the current 20%) there
> would be a major increase in the number and severity of wild fires.
>
There would be. There was. And atmosphere did go to 35 % oxygen.
With some interesting effects. Many Carboniferous plants have thick
lignine barks - probably an adaptation to retard fire.
There are a few fires in modern peat bogs. But generally wetland peat
fires are rare, and little charcoal is produced.
In carboniferous bogs, there was a lot of fusain deposition.
Apparently much of the biomass was charred by wetland fires.
Remus
wrote:
> On 17 mai, 17:32, Remus <roamu...@go.com> wrote:
>
> > On May 14, 11:22 pm, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> > wrote:
>
>
> Mars has just 0,2 mbar of nitrogen.
>
> The other atmospheres have Earth 800 mbar, Titan 1500 mbar, Venus 3200
> mbar. Why those particular numbers?
>
>
As for Earth and Venus, I am not sure
specifically how much of the Earth's
gaseous Nitrogen is locked up in life
forms. If negligible, I would suspect
that some of it might have to do with
the relative levels of interaction of
Nitrates both in the acid form and
condensed in rocks in the geology
of both Earth and Venus.
Nitrogen is a very common element
in the universe. When you consider
the total composition of Nitrogen,
Oxygen, and Carbon in a metal-rich
nebula you start wondering where
all of that Nitrogen may have gone
to when you consider how common
oxides are in the crusts of the Moon
and Mercury, Venus, Earth, and
the outer ice moons as frozen water.
This is only speculation, but the
freezing point of Ammonia is at
about the same temperature as
the freezing point of Carbon Dioxide,
and the poles of Mars have ice
caps that consist of frozen Carbon
Dioxide.
I would guess that it might be possible
that Nitrogen on Mars might be locked
up in the crust of Mars as complexes
of ammonia with the rocks that form at
the lower temperatures. It might be that
the geochemistry of Mars favored
Ammonia over free Nitrogen, and
that the Ammonia is then condensed
into the crust at the low Martian
temperatures. Mars is way too hot
for liquid or solid Nitrogen but not
liquid or solid Ammonia. Then again,
maybe not. I am not sure of the
relative abundance of Ammonia vapor
on Mars in comparison with Nitrogen,
and Wikipedia seems to list Nitrogen
as the second most common component
of Mars's atmosphere after CO2, but
doesn't have a listing for Ammonia vapor.
It seems to indicate that about 25%
of Mars's atmospheric CO2 is locked
up in the ice caps, but doesn't seem to
show if there is any liquid or solid
ammonia as an ice cap component.
http://en.wikipedia.org/wiki/Atmosphere_of_Mars
http://en.wikipedia.org/wiki/Climate_of_Mars
http://en.wikipedia.org/wiki/Geology_of_Mars
http://en.wikipedia.org/wiki/Ammonia
Nitrogen is a very common element
in the universe. When you consider
the total composition of Nitrogen,
Oxygen, and Carbon in a metal-rich
nebula before stellar ignition you start
wondering where all of that Nitrogen may
have gone to when you consider how
common oxides are in the crusts of the
Moon and Mercury, Venus, Earth, and
the outer ice moons as frozen water.
Probably during the early formation of
the solar system when the Sun first
started shining it was able to from
the early solar radiation drive many
of the more volatile components of
the smaller solar system's
non-hydrogen-helium ring fragments
away at places closer to the star, making
asteroids in the inner solar system and
comets in the outer solar system. It
might be that Nitrogen complexed less
well than Oxygen with the heavy metals
in the inner asteroids, leaving it only
as Ammonia in the outer comets.
Then those smaller fragments came
together to form planetesimals or
added to the condensing planetesimals'
mass.
It seems an interesting subject however,
and this is only speculation. When
you consider that the Earth's atmosphere
is about 4/5ths Nitrogen, one would think
that would be at least a somewhat vital
subject to be acquainted with regardless
of whether in its fixed form, it would help
plants grow or not.
Remus
wrote:
> On 18 mai, 00:26, pyotr filipivich <ph...@mindspring.com> wrote:
>
>
>
> > [Default] I missed the Staff meeting, but the Memos showed that
> > MWillMar...@gmail.com wrote on Thu, 15 May 2008 08:59:51 -0700 (PDT)
> > in soc.history.what-if :
>
> > >On May 14, 11:22 pm, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> > >wrote:
>
> > >> So, what would be the minimum mass of habitable planet?
>
> > >Titan manages a 1.5 bar pressure despite being smaller than Mars.
> > >Granted, it's cold.
>
> > >Can you even have a pure oxygen atmosphere without anything else?
>
> > A pure Oxygen atmosphere will not last a long time, due to the
> > reaction of oxygen with anything it can.
>
> Anything it can, but it cannot react with everything.
>
> > I recall reading that if the
> > atmosphere were to go over 25% oxygen (up from the current 20%) there
> > would be a major increase in the number and severity of wild fires.
>
> There would be. There was. And atmosphere did go to 35 % oxygen.
What specific evidence is there for large changes
in the composition of Oxygen or Carbon Dioxide
in the Earths atmosphere during the Phanerozoic
eon?
I've seen enough wild claims based upon the
molecular clock hypothesis to relegate most
of them to popular news mis-reporting and
junk science.
As far as this is concerned I am not entirely
sure. What specific types of probably
isotopic counting methods have lead to the
idea that there were large variations in
the composition of the Earth's atmosphere
in the last 500 million years? Are these
methods prone to error or is the idea
that the atmosphere has this significantly
changed in these more recent times well
founded?
pyotr filipivich
2008 14:21:12 -0700 (PDT) in soc.history.what-if :
>
>> >Can you even have a pure oxygen atmosphere without anything else?
>>
>> A pure Oxygen atmosphere will not last a long time, due to the
>> reaction of oxygen with anything it can.
>
>Anything it can, but it cannot react with everything.
True. "It all depends." Aluminum forms a tightly bound oxide,
effectively preventing further oxidation of the material. Iron, OTOH,
forms an oxide which "flakes" off - exposing more material. Of
course, in our current condition, most of that has already happened,
but ...
Oxygen is reactive, exceeded only by Fluorine, iirc. There is a
deranged part of me which would like to see a Fluorine breathing life
form, but it would be ... different.
pyotr
pyotr filipivich
soc.history.what-if :
There were all sorts of contributing factors to make the fire
"really bad" - like a hatch which required minutes to open.
But 100% O2 at standard atmospheric pressure was the number one
problem. :-)
>
>pt
Tim McDaniel
pyotr filipivich <ph...@mindspring.com> wrote:
> Oxygen is reactive, exceeded only by Fluorine, iirc. There is
>a deranged part of me which would like to see a Fluorine breathing
>life form, but it would be ... different.
There was a lovely article I read, I believe in Boy's Life (which
would put it in the 1970s). The premise was to design an
extraterrestrial horror. The author started with a fluorine-breathing
giant land lobster under a ultraviolet-heavy sun. But the author
pointed out the square-cube law and the problem of gas exchange
through the skin, so he changed the monster to have an endoskeleton
and lungs. He pointed out that fluorine, being highly reactive,
needed lots of energy to be broken apart, hence the ultraviolet light
... but it's opaque to ultraviolet light and not so transparent in the
visible, and chlorine isn't much better, so he went to oxygen and
visible light. The end result of all the tweaks was pretty much a T
rex. The lesson, of course, was that there are biological, chemical,
and physical constraints on life.
--
Tim McDaniel; Reply-To: tm...@panix.com
George W Harris
<ph...@mindspring.com> wrote:
> Oxygen is reactive, exceeded only by Fluorine, iirc. There is a
>deranged part of me which would like to see a Fluorine breathing life
>form, but it would be ... different.
There is an H. Beam Piper novel, "Uller Uprising",
which features flourine-based life forms.
>
>pyotr
--
Doesn't the fact that there are *exactly* 50 states seem a little suspicious?
George W. Harris For actual email address, replace each 'u' with an 'i'
Alfred Montestruc
wrote:
> What is the minimum mass of a habitable planet?
Depends on the mean temperature of the planet.
See the site below for a discussion.
http://www.astro.princeton.edu/~strauss/FRS113/writeup3/index.html
He is wrong in one thing namely that the escape speed from earth is 11
km/sec not 7, but it is 7 miles/sec
Anyway the tail of the Boltzmann speed distribution of molecules of a
given molecular weight is a major player as is the fact that the
temperature of the earth's upper atmosphere (not the stratosphere,
much higher up) is as high as 1000 C.
better discussion below.
http://cseligman.com/text/planets/retention.htm
Bottom line the ratio of the escape speed of that planet to the mean
speed at the temperature of interest is very important. Quoting from
the second site.
--------------quote
The rate of loss of an atmosphere depends upon the ratio of escape
velocity to average particle speed in the upper atmosphere. IF THE
RATIO IS 5, THE ATMOSPHERE ESCAPES IN TIMES OF THE ORDER OF 100
MILLION YEARS. (General agreement about this result).
As the ratio goes down (4, 3, etc) the atmosphere escapes much more
rapidly (100 to 1000 times more rapidly for each unit change,
depending upon the reference consulted), and as it goes up (6, 7, etc)
the atmosphere escapes much more slowly (100 to 1000 times more
slowly, as per previous statement).
Hence, times to escape are:
About 100 million years, if ratio is 5.
Well under 1 million years, if ratio is 4 (more particles in high-
velocity tail).
Well under 10 thousand years, if ratio is 3 (still more high-velocity
particles).
Well over 10 billion years, if ratio is 6 (fewer high-velocity
particles).
Well over 1 trillion years, if ratio is 7 (still fewer high-velocity
particles).
SO, NORMAL GASES, with ratio of 16 to 20, are held onto forever (as we
might expect, since we're breathing them, after 4.5 billion years of
Earth history).
HOWEVER, lighter gases move faster (at atomic level) than heavy ones,
because Temperature is proportional to particle mass, as well as
square of speed. Oxygen atoms move 40% faster than oxygen molecules,
helium atoms move 4 times faster, and hydrogen atoms move almost 6
times faster, than the "average" of normal particles. Therefore, the
ratio of 16 to 20 times for normal air molecules is cut to 11 to 14
for oxygen atoms (still high enough to hold on, forever and ever), 4
to 5 for helium (lost in times of the order of millions to tens of
millions of years), and 3 (plus or minus) for hydrogen (lost in times
of the order of thousands or tens of thousands of years).
IN OTHER WORDS, the Earth can hold onto either molecular or atomic
nitrogen and oxygen, but slowly loses helium, and more rapidly loses
hydrogen, so that over long periods of time, all the hydrogen and
helium in the atmosphere should slowly leak into space.
--------------
So if we take the ratio of 7 as being ideal, set the maximum
temperature you can expect of the upper atmosphere, specify the
required gases (oxygen-nitrogen-water vapor) then solve for the
minimum mass the planet must have to hold an atmosphere for 1
trillion years.
Crown-Horned Snorkack
> [Default] I missed the Staff meeting, but the Memos showed that
> 2008 14:21:12 -0700 (PDT) in soc.history.what-if :
>
>
>
> >> >Can you even have a pure oxygen atmosphere without anything else?
>
> >> A pure Oxygen atmosphere will not last a long time, due to the
> >> reaction of oxygen with anything it can.
>
> >Anything it can, but it cannot react with everything.
>
> True. "It all depends." Aluminum forms a tightly bound oxide,
> effectively preventing further oxidation of the material. Iron, OTOH,
> forms an oxide which "flakes" off - exposing more material. Of
> course, in our current condition, most of that has already happened,
Indeed. And most of iron has sunk into the core of Earth. There is no
metallic aluminum on Earth.
Russell Wallace
> Oxygen is reactive, exceeded only by Fluorine, iirc. There is a
> deranged part of me which would like to see a Fluorine breathing life
> form, but it would be ... different.
I asked awhile ago about the possibility of a chlorine-breathing life
form. (Chlorine having similar properties to fluorine, only somewhat
less so.) Sadly, the answer was no; apparently being held together by
only a single bond makes chlorine molecules react more readily than
oxygen molecules, to the point where a living cell suffused with
chlorine would find its constituent molecules rapidly broken down.
Remus
Indeed. If you genetically re-engineered human
beings to be able to live in vacuum, the Moon
or Mars might be habitable now. Much of
space is habitable to someone in a space
suit. Of course, if it is a matter of being
able to not have to ship resources from the
Earth to be able to maintain habitability,
then the problem of habitability would be
one of obtaining resources from the local
environment, and not one involving
terraforming.
Alfred Montestruc
Taking the minimum ratio as 7 such that you have a permanent (trillion
year) atmosphere with water vapor so that your planet will not rapidly
lose water, and if you hold the temperature of the thermosphere
constant (hot part of the outer atms at about 1167 Kelvin), and the
density of the planet constant and the same as the earth, then the
minimum mass of the planet works out to 2.97 e+24 kg or 49.7% of one
earth mass. Holding the density constant means that planet will be
79.2% of the diameter of the earth.
Mess with the density and it changes. If you want I will email you a
spreadsheet so you can solve for it.
Crown-Horned Snorkack
> On May 15, 1:22 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> wrote:
>
> > What is the minimum mass of a habitable planet?
>
> Depends on the mean temperature of the planet.
>
> See the site below for a discussion.
>
> http://www.astro.princeton.edu/~strauss/FRS113/writeup3/index.html
>
> He is wrong in one thing namely that the escape speed from earth is 11
> km/sec not 7, but it is 7 miles/sec
>
> Anyway the tail of the Boltzmann speed distribution of molecules of a
> given molecular weight is a major player as is the fact that the
> temperature of the earth's upper atmosphere (not the stratosphere,
> much higher up) is as high as 1000 C.
>
Observe that Titan has massive atmosphere. Ganymede is more massive -
and lacks atmosphere.
Andrew Usher
wrote:
> On 19 mai, 08:59, Alfred Montestruc <montest...@gmail.com> wrote:
>
> > On May 15, 1:22 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> > wrote:
>
> > > What is the minimum mass of a habitable planet?
>
> > Depends on the mean temperature of the planet.
>
> > See the site below for a discussion.
>
> >http://www.astro.princeton.edu/~strauss/FRS113/writeup3/index.html
>
> > He is wrong in one thing namely that the escape speed from earth is 11
> > km/sec not 7, but it is 7 miles/sec
>
> > Anyway the tail of the Boltzmann speed distribution of molecules of a
> > given molecular weight is a major player as is the fact that the
> > temperature of the earth's upper atmosphere (not the stratosphere,
> > much higher up) is as high as 1000 C.
>
> What are the exosphere temperatures of Venus and Mars?
>
I believe they are much colder than Earth. This is because CO2 is an
efficient radiator of thermal energy and cools the thermosphere (which
is
optically thin at all wavelengths, of course). Earth's atmosphere
however
has less than 0.05% of greenhouse gases. This site:
http://solarphysics.livingreviews.org/open?pubNo=lrsp-2007-3&page=articlesu24.html
gives 290 K for Venus and 220-240 K for Mars.
Indeed, Mars could not hold its current atmosphere if its exospheric
temperature equaled Earth's.
Andrew Usher
Alfred Montestruc
wrote:
> On 19 mai, 08:59, AlfredMontestruc<montest...@gmail.com> wrote:
>
> > On May 15, 1:22 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> > wrote:
>
> > > What is the minimum mass of a habitable planet?
>
> > Depends on the mean temperature of the planet.
>
> > See the site below for a discussion.
>
> >http://www.astro.princeton.edu/~strauss/FRS113/writeup3/index.html
>
> > He is wrong in one thing namely that the escape speed from earth is 11
> > km/sec not 7, but it is 7 miles/sec
>
> > Anyway the tail of the Boltzmann speed distribution of molecules of a
> > given molecular weight is a major player as is the fact that the
> > temperature of the earth's upper atmosphere (not the stratosphere,
> > much higher up) is as high as 1000 C.
>
> What are the exosphere temperatures of Venus and Mars?
I do not know off hand, however I think they are much lower than that
of the earth, and I strongly suspect it may have a lot to do with the
earth having a substantial magnetic field while Venus and Mars do not.
Andrew Usher
> On May 20, 12:13 pm, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> wrote:
>
>
>
> > On 19 mai, 08:59, AlfredMontestruc<montest...@gmail.com> wrote:
>
> > > On May 15, 1:22 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> > > wrote:
>
> > > > What is the minimum mass of a habitable planet?
>
> > > Depends on the mean temperature of the planet.
>
> > > See the site below for a discussion.
>
> > >http://www.astro.princeton.edu/~strauss/FRS113/writeup3/index.html
>
> > > He is wrong in one thing namely that the escape speed from earth is 11
> > > km/sec not 7, but it is 7 miles/sec
>
> > > Anyway the tail of the Boltzmann speed distribution of molecules of a
> > > given molecular weight is a major player as is the fact that the
> > > temperature of the earth's upper atmosphere (not the stratosphere,
> > > much higher up) is as high as 1000 C.
>
> > What are the exosphere temperatures of Venus and Mars?
>
> I do not know off hand, however I think they are much lower than that
> of the earth, and I strongly suspect it may have a lot to do with the
> earth having a substantial magnetic field while Venus and Mars do not.
As I just stated in my last post, it is because of their high CO2
concentration.
Andrew Usher
Crown-Horned Snorkack
> On May 20, 11:13 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> wrote:
>
>
>
> > On 19 mai, 08:59, Alfred Montestruc <montest...@gmail.com> wrote:
>
> > > On May 15, 1:22 am, Crown-Horned Snorkack <chornedsnork...@hush.ai>
> > > wrote:
>
> > > > What is the minimum mass of a habitable planet?
>
> > > Depends on the mean temperature of the planet.
>
> > > See the site below for a discussion.
>
> > >http://www.astro.princeton.edu/~strauss/FRS113/writeup3/index.html
>
> > > He is wrong in one thing namely that the escape speed from earth is 11
> > > km/sec not 7, but it is 7 miles/sec
>
> > > Anyway the tail of the Boltzmann speed distribution of molecules of a
> > > given molecular weight is a major player as is the fact that the
> > > temperature of the earth's upper atmosphere (not the stratosphere,
> > > much higher up) is as high as 1000 C.
>
> > What are the exosphere temperatures of Venus and Mars?
>
> I believe they are much colder than Earth. This is because CO2 is an
> efficient radiator of thermal energy and cools the thermosphere (which
> is
> optically thin at all wavelengths, of course). Earth's atmosphere
> however
> has less than 0.05% of greenhouse gases. This site:
>
>
> gives 290 K for Venus and 220-240 K for Mars.
>
> Indeed, Mars could not hold its current atmosphere if its exospheric
> temperature equaled Earth's.
>
> Andrew Usher
So, how hot would the exosphere of Mars get if Mars had just 10 %
carbon dioxide and 90 % oxygen?
Brian Davis
wrote:
> So, how hot would the exosphere of Mars get if Mars had just 10 %
> carbon dioxide and 90 % oxygen?
Short answer - I don't know.
Exosphere temperatures are really tricky things to calculate IMS. The
energy inputs to the exosphere are not terribly well characterized,
but include incoming solar radiation as well as solar wind
interactions (hey, when your atmosphere is so then that it's
collisionally thin, stuff like solar wind or magnetic field
interactions start playing a role). You *could* assume that it scales
linearly with CO2 concentration... but while I'm usually a fan of
first-order approximations, here I wouldn't trust it.
Jeans escape of the atmosphere is only a very very rough first cut at
atmospheric lifetime anyway. Look at methane on Titan, or the wildly
varying exosphere temperatures of the terrestrials, or complications
like impact stripping of the atmosphere.
--
Brian Davis
Russell Wallace
> I believe they are much colder than Earth. This is because CO2 is an
> efficient radiator of thermal energy and cools the thermosphere (which
> is
> optically thin at all wavelengths, of course). Earth's atmosphere
> however
> has less than 0.05% of greenhouse gases. This site:
>
> http://solarphysics.livingreviews.org/open?pubNo=lrsp-2007-3&page=articlesu24.html
>
> gives 290 K for Venus and 220-240 K for Mars.
>
> Indeed, Mars could not hold its current atmosphere if its exospheric
> temperature equaled Earth's.
I'm confused here.
Mars escape velocity = 5 km/s.
Nitrogen average molecular velocity in Earth's exosphere = 600-800 m/s?
Ratio = 6-8?
So at the same exosphere temperature, Mars should be able to hold
nitrogen. I don't understand why it didn't.
But if Mars exosphere temperature = 240 K, then average molecular
velocity for nitrogen is less than 300 m/s. Ratio is over 15.
Molecular weight of N2 = 28.
Molecular weight of helium = 4.
28 / 4 = 7
sqrt(7) = 2.646
2.646 * 300 = 793.
5000 / 793 = 6.3
So Mars should be marginally able to hold helium, let alone nitrogen.
What am I missing?
Robert Martinu
> I'm confused here.
>
> Mars escape velocity = 5 km/s.
>
> Nitrogen average molecular velocity in Earth's exosphere = 600-800 m/s?
> Ratio = 6-8?
> So at the same exosphere temperature, Mars should be able to hold
> nitrogen. I don't understand why it didn't.
> What am I missing?
The point is "average".
Wich means, that some molecules in the upper atmosphere are faster, a
few even much faster.
Certainly not many, but then you have lots of time to loose the gas.
Russell Wallace
> The point is "average".
> Wich means, that some molecules in the upper atmosphere are faster, a
> few even much faster.
> Certainly not many, but then you have lots of time to loose the gas.
Yes, that's why the escape velocity needs to be several times the
average molecular velocity. Specifically, according to the web page an
earlier poster linked and quoted from, at least 6-7 times the average
velocity - which criterion Mars more than meets.
Brian Davis
<russell.wallace.nos...@gmail.invalid> wrote:
> > gives 290 K for Venus and 220-240 K for Mars.
>
> > Indeed, Mars could not hold its current atmosphere if its exospheric
> > temperature equaled Earth's.
>
> I'm confused here.
>
> Mars escape velocity = 5 km/s.
> Nitrogen average molecular velocity in Earth's exosphere = 600-800 m/s?
I get about 940 m/s, but pretty close, giving a ratio of Vesc/Vrms =
5.3. That would tend to imply a lifetime in the 10's of millions of
years (if you use a simple Jeans escape model). Not forever, but
(remember the point of this thread) a very very VERY long time, for
terraforming.
> But if Mars exosphere temperature = 240 K, then average molecular
> velocity for nitrogen is less than 300 m/s. Ratio is over 15.
Yep, that's what I get as well. If you map the "retentivity" (Vesc/
Vrms) of various objects in the solar system, you find that Earth is
around 30, Venus at 25, then Mars comes in at 15, Titan 12, and things
like Ganymede (11), Triton (10ish), Io (10) all come in under that.
Since Titan has retained a thick atmosphere while Mars rather clearly
hasn't, the conclusion is that putting a lot of worldbuilding faith in
a simple Jeans escape model is probably a really bad idea. One of my
textbooks makes a nice sidebar of this, pointing out that with a
realistic thermal structure, atmospheric escape can be as much as 10^6
times faster than a simple Jeans escape model.
> What am I missing?
Not much, except when to realize that some of the approximations
tossed around (here in rasfs or even in the "proper" literature) are
admittedly really really bad approximations... "extreme lower limits"
might be a better term.
--
Brian Davis
Juergen Poniatowski
<chorned...@hush.ai> wrote:
>On 15 mai, 22:56, Brian Davis <brda...@iusb.edu> wrote:
>> On May 15, 12:40 pm, Bernard Peek <b...@shrdlu.com> wrote:
>>
>> > Oxygen gas is so reactive that it's unlikely to be found free except
>> > where there is a process that continually generates it.
>>
>> There are others ways of producing oxygen besides biology - like
>> having global oceans (or even ice - think Europa), and UV-
>> disassociating the water leaving O2 as the H escapes. The trick is not
>> to have a copious source of O2, but to have matched source and sink
>> rates. Put all your reduced material deep under an ocean, or an ice
>> sheet, and you can build up significant O2... but this probably isn't
>> "habitable" in the sense the poster wanted either.
>>
>> > Can you even have a pure oxygen atmosphere without anything else?
>>
>> Well... I suspect it's unlikely, but I can't think of a reason why
>> it's not possible. For terrestrial life there would be some issues -
>> you need at least a certain (trace) level of CO2 for terrestrial
>> plants (at 150 ppm at 1 Atm C3 plants are really at a standstill, so
>> lower than this all you'd have is C4's or maybe CAM-based
>> photosynthesis), but it's really trace. A bigger issue that I don't
>> know the limits on is N2 fixation - this is rather flaky & delicate
>> now (with 0.78 Atm of N2 handy, and only 0.2 Atm O2), and I've no idea
>> how low you can go on pN2 before nitrogen fixation essentially stops.
>> And that's a rather hard limit for an unassisted terrestrial biosphere
>> to cross.
>>
>Back in Carboniferous, when the atmosphere had something like 0,4 atm
>oxygen, did the extra oxygen interfere with nitrogen fixation?
There was a considerable different atmospheric composition...
But,
Does anybody know what was the ABSOLUTE atmospheric pressure during
the Carboniferous (and other ancient) ages?
Ok, it is not even easy to define a elevation level of reference
(during ice ages the sea level was considerably (100m?) lower) but was
the pressure about the same as today?
That means something between 950 and 1050mbar?
Maybe higher?
During time gas is lost to space, but how much per Million years?
How can you calculate the yearly loss of Gas of a given atmosphere
(compositon?, Gass mass?) on a Planet mith Mass M and Radius R
?
just curious,
JP
Brian Davis
> Does anybody know what was the ABSOLUTE atmospheric pressure during
> the Carboniferous (and other ancient) ages?
I'm not sure we do... but there is strong evidence it hasn't changed
too much during that time. To change pressure, you'd have to change
the amount of gas, and *most* (all though not all) ways of doing that
would leave isotopic evidence.
> How can you calculate the yearly loss of Gas of a given atmosphere
> (compositon?, Gass mass?) on a Planet mith Mass M and Radius R
> ?
Read back through this thread, and research "Jeans escape". The
problem is while you can make some simple assumptions and calculate
from there, the real situation is much more complex, and the process
is often so sensitive that such "simple approximations" are almost
worthless.
--
Brian Davis
Andrew Usher
> On May 25, 3:06 pm, Juergen Poniatowski <juerg...@gmx.de> wrote:
>
> > Does anybody know what was the ABSOLUTE atmospheric pressure during
> > the Carboniferous (and other ancient) ages?
>
> I'm not sure we do... but there is strong evidence it hasn't changed
> too much during that time. To change pressure, you'd have to change
> the amount of gas, and *most* (all though not all) ways of doing that
> would leave isotopic evidence.
The main constituent of Earth's atmosphere is nitrogen, which is
inert. How
do we determine if the partial pressure of nitrogen has changed
through
geologic history? Since any significant change would have to be
inorganic,
it shouldn't leave any isotopic evidence. In fact, do we even know the
amount
of nitrogen in the whole Earth? - I've never seen any research on it.
Andrew Usher
Brian Davis
> The main constituent of Earth's atmosphere is nitrogen, which is
> inert. How do we determine if the partial pressure of nitrogen has changed
> through geologic history?
Well, for a start, it's hard to see how you could have lost or gained
too much without some isotopic fractionation. And isotopic
fractionation pretty much occurs... well, almost always. In nearly all
chemical reactions (organic ones are just a subset), for instance. As
for loss from the Earth via thermal energy (Jean's escape), that
*certainly* will induce some significant fractionation.
> In fact, do we even know the amount of nitrogen in the whole Earth?
Do a little research on the subject - a quick Google pulls up plenty
of tidbits.
--
Brian Davis
JHR
> But,
> Does anybody know what was the ABSOLUTE atmospheric pressure during
> the Carboniferous (and other ancient) ages?
> Ok, it is not even easy to define a elevation level of reference
> (during ice ages the sea level was considerably (100m?) lower) but was
> the pressure about the same as today?
> That means something between 950 and 1050mbar?
> Maybe higher?
> During time gas is lost to space, but how much per Million years?
> How can you calculate the yearly loss of Gas of a given atmosphere
> (compositon?, Gass mass?) on a Planet mith Mass M and Radius R
> ?
>
> just curious,
> JP
Hi JP.
Judging from biological markers such as the former size and wing span
of flying creatures as opposed to recent ones, I personally put it at
roughly 2-3 times the atmospheric height, volume, density and pressure
of today.
I do realize that this is not a scientific statement. However, it
should not be too difficult for engineers and biologists to work that
one out in better approximation.
See http://home.pages.at/jhinrichs/c1-a1.html for more detail.
:-)
JHR
veritas
Jesus Christ, if we had the answers to all these questions would we be
sending landers to Mars to study it? I don't think so. I believe a
lot of these questions are trying to be answered now. We really don't
know most of them. I'm not engineer or a biologists but surely
someone would have come up with some better answers if they knew for
sure. So, we keep looking. Ken Hogan
Brian Davis
> Judging from biological markers such as the former size and wing span
> of flying creatures as opposed to recent ones, I personally put it at
> roughly 2-3 times the atmospheric height, volume, density and pressure
> of today.
>
> I do realize that this is not a scientific statement.
Well, how about making it a scientific statement? Or even doing a
basic lit search? I've got books from some time ago that propose the
same things you do (or much more outrageous ones - like reduced
gravity). There might be a reason these aren't the accepted reasons
(and yes, biologists & biophysicists have looked into these issues
before).
--
Brian Davis
Bryan Derksen
> Michael G. Koerner wrote:
>> Both are losing atmosphere, but it both cases it is at an equilibrium
>> with replenishment through volcanic activity.
>
> And it is the lighter components for the most part escaping.
This is why Venus no longer has significant quantities of water, BTW.
The water molecules dissociate in the upper atmosphere and the hydrogen
easily escapes.
>> Also, as for a magnetic field, it also protects the inhabitants from
>> cosmic radiation, something that would be fatal to life without it.
>
> Not sure the magnetic field is all that critical. The atmosphere already
> provides a reasonable amount of protection from most solar storm charged
> particles. In density terms roughly equivalent I suppose to 32 foot of
> water. Mutation rates would be higher with no magnetic field.
Mutation rates are strongly affected by the strength of the cell's DNA
repair mechanisms, which are adjusted via evolution. I suspect that
unless you're cranking the background radiation _way_ up you'll wind up
with life adjusting to have a mutation rate similar to what you'd have
with the magnetic field intact.