They only have a whole planet to search...

[apestench]

Does it bother anyone else the way sci-fi movies tend to treat whole planets as if they are small areas? For example, Luke Skywalker saying, after landing on Dagobah, "Now all I have to do is find this Yoda..." One creature to find and a whole planet to search? (Granted in that example the force may have led him to the right spot) This is like saying it should be easy to find Osama, we know he's somewhere on Earth.
Also, do any other planet in the sci-fi realm have individual nations? It seems the vast majority of planets have one world governments.
Just some thoughts for possible discussion.

[Swift]

Welcome apestench

Yeah, the thing about searching the planet is pretty stupid. When helpful for the plot, I remember various Star Trek episodes (both original and NG) where searching the planet was made a big issue, but it is inconsistent.

There have occasionally been Star Trek episodes where there were more than one nation on the planet, again it usually has been an important part of the plot, though it's usually just two nations. I think there have been a couple of Stargate ones like that too. My guess is the assumption is that once you have interplanetary interactions, that subdivisions below the planetary government level become less important (or disappear completely). Judging by Earth, that is true to some extent, but not completely. Even given the UN, the US government, and state and county governments, my local school board has considerable power over some issues, but that probably don't include declaring war on the Klingons. :wink:

[ToSeek]

Or the entire planet has one ecosystem: "swamp planet," "desert planet," "ice planet," etc. If it's inhabitable, how likely is that?

[The Bear]

I guess it's just a matter of keeping things simple. The writers want to have a clear villain (or at least one clear point of view), so they have the starship captain negotiate with ONE leader rather than 165 leaders. :o
Then again, it might make an interesting episode to have a starship captain try to negotiate with a planet that actually has multiple cultures, multiple forms of government, etc. Perhaps it would end up as a really looooooooooong episode, but an interesting one nonetheless.

[Grand Vizier]

To be fair to Trek (reluctantly), they do usually scan for life signs or 'tetrion emissions' or some treknobabble. Sad to say, Doctor Who used to a be a worse sinner here. Particularly in the old days, when he couldn't steer the Tardis at all (time-space capacitor was broken or something, so it just went to a randow destination) it would still always end up at a historically significant event, or the only inhabited spot on the whole planet, or right in the middle of the bad guys' installation. And for some reason it was particularly attracted by Daleks...

[ToSeek]

To be fair to Trek (reluctantly), they do usually scan for life signs or 'tetrion emissions' or some treknobabble. Sad to say, Doctor Who used to a be a worse sinner here. Particularly in the old days, when he couldn't steer the Tardis at all (time-space capacitor was broken or something, so it just went to a randow destination) it would still always end up at a historically significant event, or the only inhabited spot on the whole planet, or right in the middle of the bad guys' installation. And for some reason it was particularly attracted by Daleks...

I always figured that the TARDIS generally ended up at significant spots in space-time because the web of time had a sort of nexus there - that any sort of decision point had some sort of attractive quality to it so far as time-traveling devices are concerned.

[Swift]

I guess it's just a matter of keeping things simple. The writers want to have a clear villain (or at least one clear point of view), so they have the starship captain negotiate with ONE leader rather than 165 leaders. :o
Then again, it might make an interesting episode to have a starship captain try to negotiate with a planet that actually has multiple cultures, multiple forms of government, etc. Perhaps it would end up as a really looooooooooong episode, but an interesting one nonetheless.
An interesting idea. Too bad Enterprise didn't go that way. It might have been interesting to deal with different factions of the Klingons or the Vulcans. Maybe their own world governments didn't form until they united to deal with the Earth world government?

Thinking about it more, Babylon 5 did get into some of the political stuff. Even though Earth had a world government in that series, there were definitely factions.

[Jpax2003]

Thinking about it more, Babylon 5 did get into some of the political stuff. Even though Earth had a world government in that series, there were definitely factions.Babylon 5 did it well, but could have been better. I am a big fan of B5 but admit it was only mentioned culture where it was necessary to the major storyline. There was politiking in the Earth Alliance and the Minbari Federation, but not much anywhere else. There were differences between the two Vorlons we saw, but they were ultra-powerful individuals, not necessarily significant of different Vorlon cultures. The Centauri had class structure, battling houses of nobility, and different dialects, but nothing indicative of separate cultures. The Narn were one people, but kinda expected after 100 years of abject slavery by the Centauri. The other alien civilizations were mostly single cultures, and were often treated as a single political bloc, except for the ocasional foray into Drazi purple and green "culture".

[Grand Vizier]

To be fair to Trek (reluctantly), they do usually scan for life signs or 'tetrion emissions' or some treknobabble. Sad to say, Doctor Who used to a be a worse sinner here. Particularly in the old days, when he couldn't steer the Tardis at all (time-space capacitor was broken or something, so it just went to a randow destination) it would still always end up at a historically significant event, or the only inhabited spot on the whole planet, or right in the middle of the bad guys' installation. And for some reason it was particularly attracted by Daleks...

I always figured that the TARDIS generally ended up at significant spots in space-time because the web of time had a sort of nexus there - that any sort of decision point had some sort of attractive quality to it so far as time-traveling devices are concerned.

They kept changing the rationale later on. (For example, the Timelords stuck Doctor #3 on Earth for ages, which was a bit tiresome of them, I thought.) It was always a bit vague really.

But Doctors #1 and #2 definitely couldn't steer, and I don't remember anything about the Tardis being attracted to anything. But I could be wrong - I don't know what's canonical in the Hoovian world these days. They were definitely sometimes pulled in by someone meddling with the space-time continuum, though.

[papageno]

Or the entire planet has one ecosystem: "swamp planet," "desert planet," "ice planet," etc.

Or a "third-rate variety show" planet. :)

[Humots]

I believe Jerry Pournelle called this the "it was raining on Mongo that morning" fallacy.

I could believe in an ice planet. Earth is supposed to have been pretty much an ice planet (glaciers from pole to pole) during one of the pre-human ice ages.

Also, I believe there is a "White Earth" environment catastrophe, where the planet freezes up permanently. I don't know how cold it would get, but I'd bet it would be more than just winter everywhere, all the time.

[Humphrey]

I could see a habitable swamp like planet.

Desert planet would just be stupid. How the planet makes breathable air is beyond me.

[PhantomWolf]

Or the entire planet has one ecosystem: "swamp planet," "desert planet," "ice planet," etc. If it's inhabitable, how likely is that?

These seem to be shots at Dagobah, Tatoonie, and Hoth respectively?

Actually none of them are exclusively one terrain type as such. Tatoonie tends to have quite different desert terrains, consider Mars, but bigger and hotter. It has sand dunes, salt flats, mountains, canyons, vast rocky plains, and even a few greener areas where there is more mositure. The difference between Tatoonie and Mars is that due to Tatoonie being much hotter, it doesn't have the ability to sustain ice caps of any sort. Also that Tatooine does have areas of mositure and plant life. (These oasis tend to be well gaurded and protected by the sand peoples or Jawas, though not all.) Remember that Bantha and Dewbacks need to be able to eat. Even on Earth most desert has plant life in it.

Hoth has regions where it is not entirely polar and during it's "summer" their are areas above and below the equator that defrost to allow lichens and other plants to grow. There are the main source of food for the Tauntauns. There are also hot springs and volcanic vents that also provide habitable areas and planet life. Hoth also has massive oceans under its ice, teeming with algae and plankton type life which when ejected from the oceans by the tides created by its three moons also provide food sources for creatures. Again Mars would be a good example here. Hoth would be what Mars would be if it had more mostiure and was slightly further from the sun.

Dagobah is closer to a jungle world than a total swamp, though there is a lot of sawmp. It does have mountainous regions and lakes as well though. With vast stretches of rain forests and a high humidity, the surface of Dagobah has become rather soggy as a whole, but there are other areas beside that Luke and Yoda were.

I think that one mistake that is made is assuming that all the planet is like the little area shown. The forest moon of Endor was shown as a huge redwood forest, but this misses the grasslands, lakes, seas, rivers, mountains and other areas of the moon that were nothing like the forested parts.

About the only planets I know of in the SW Universe that could truely be said to have a single terrain would be Komino and Mon Calamari which are both water worlds with small muddy islands. Coruscant could be, except it is just a planet sized city whereas once it was similar to Earth.

[Invader Spleen]

can all be explained by $$$, the mysterious source of power of these universes gods, known as 'The Producers'

[CTM VT 2K]

can all be explained by $$$, the mysterious source of power of these universes gods, known as 'The Producers'

Are you trying to tell me that the great and powerful "Producers" are motivated by $? [-X
Say it isn't so! Certainly they are motivated by an altruistic nature and the search for truth.... :^o :wink:

[Chip]

I guess it's just a matter of keeping things simple. The writers want to have a clear villain (or at least one clear point of view), so they have the starship captain negotiate with ONE leader rather than 165 leaders. :o
Then again, it might make an interesting episode to have a starship captain try to negotiate with a planet that actually has multiple cultures, multiple forms of government...

You may recall in the movie Day the Earth Stood Still, the central character, Klaatu, was somewhat surprised to find that the various leaders of Earth would not talk to him if he held his meeting in the location of a rival nation. He somewhat solved that problem by throwing the "Earth off-switch" for an hour. He nevertheless ended up making his speech to the scientists representing the countries.

I always figured that the TARDIS generally ended up at significant spots in space-time because the web of time had a sort of nexus there - that any sort of decision point had some sort of attractive quality to it so far as time-traveling devices are concerned.

I always thought it was more to do with the proximity of Leighton-Buzzard's ubiquitous sand-pits to Elstree Sudios? :D

Now, where did I leave my Sonic Screwdriver? I think one of my transponders has broken... 8-[ 8-[ 8-[ #-o

Come along now, Susan - we need to get to Metabeelis-3! :oops: :roll:

[eburacum45]

The problems of searching a planet pale against the problems of searching an artificial megastructure like a ringworld or dyson sphere;

but characters seem to have no problems in that regard either.

[ToSeek]

Or the entire planet has one ecosystem: "swamp planet," "desert planet," "ice planet," etc. If it's inhabitable, how likely is that?

These seem to be shots at Dagobah, Tatoonie, and Hoth respectively?


I was thinking of those, but just as examples of a wider phenomenon. I have the impression that Star Trek and other programs have succumbed to similar generalizations.

[AndrewGPaul]

desert and ice planets seem reasonable to me, if they're on the extremes of the habitable zone of their star. a planet-wide swamp (or redwood forest) seems less obvious, but I'm sure someone could explain it, with a modicum of handwaving :)

[The Supreme Canuck]

I can see desert or frozen planets, just not with a breathable atmosphere. In fact, we have a few just next door...

[Humphrey]

Well technically a ice planet can have air if its water ice. Just need someway to seperate the molecules.

[The Supreme Canuck]

But then we'd have a lot of hydrogen in the atmosphere. Would it be breathable?

[PhantomWolf]

But then we'd have a lot of hydrogen in the atmosphere. Would it be breathable?
Why? Just because there is a layer of ice water doesn't mean that the atmosphere can't be a Nitrogen/Oxygen mix, especially when there are alges and planktons in the oceans. Are the levels of Hydrogen greater in the Artic or Antartic?

[Mellow]

It is still the concept of a desert planet that gets me annoyed, simply because I can't fathom from where ay sustainable / recycling atmosphere could be maintained.

Unless..... It's sand Jim, but not as we know it....

[PhantomWolf]

It is still the concept of a desert planet that gets me annoyed, simply because I can't fathom from where ay sustainable / recycling atmosphere could be maintained.

Unless..... It's sand Jim, but not as we know it....

That's because you are assuming that a desert is barren of life. They aren't though, lichens, fungi, cacti, wildflowers, grasses, shrubs and trees can all live in a desert environment. You're making the mistake of assuming that all of a desert planet would be covered in dunes.

[Mellow]

Hmm, yes I understand that, I'm just not overly convinced that lichen could produce enough breathable air of whatever composition.

I guess I'm thinking about the size of the "air factory" if you like. Perhaps my mistake is to assume you'd need a big "air factory" like the Algae in earth's oceans.

Incidentally, I love it when people call the rain forests the lungs of the earth or similar, nice bit of bad biology. Nobody thanks the oceans...

So, not a well thought out issue that I have, just a gut reaction to what I'm shown on television and film. There, desert planets are just miles and miles of sand. I don't recall seeing cacti or anything on Dune and Star Wars IV. Apologies to the fans if I'm incorrect in that... :D

[Mellow]

By the way, I do believe there's a certain degree of debate about the absolute figures....


Incidentally, I love it when people call the rain forests the lungs of the earth or similar, nice bit of bad biology. Nobody thanks the oceans...

And I'd like to point out, I'm a big fan of the rainforests lest anyone think otherwise.

Ta
:D

[PhantomWolf]

Hmm, yes I understand that, I'm just not overly convinced that lichen could produce enough breathable air of whatever composition.

I guess I'm thinking about the size of the "air factory" if you like. Perhaps my mistake is to assume you'd need a big "air factory" like the Algae in earth's oceans.

More likely you're assuming that you -need- an air factory like the algae in the oceans. Without oceans you do have a lot more room for land plants to grow, vasting increasing the numbers and thus the output, you might not get sea level concentrations of oxygen, but humns can live on lesser amounts (consider high altitude.)


So, not a well thought out issue that I have, just a gut reaction to what I'm shown on television and film. There, desert planets are just miles and miles of sand. I don't recall seeing cacti or anything on Dune and Star Wars IV. Apologies to the fans if I'm incorrect in that... :D

Again, seeing part of the planet doesn't show you its entire surface any more than viewing a documentary on the Sahara shows you all of Earth's. Most of the scenes in SW's on Tatooine occur in a small area of the planet, mostly near the Dune Sea, however other areas are shown as well that are more rocky and even green about areas such as Mos Eisley.

[eburacum45]

It is possible to have a planet with an atmosphere rich in oxygen and with little or no photosynthesis;

Most of the oxygen in our own atmosphere was not created by the plants we have on Earth today, so an Earth-like world could lose all its atmosphere and retain a high oxygen level for tens of millions of years.

Addiionally an atmosphere of a waterworld about the size of the Earth might have an atmosphere rich in oxygen; water vapour in the atmosphere could be split by photolysis, the hydrogen would excape, leaving the oxygen. Depending on what other components exist in the planet's atmosphere you might get a breathable mix with no life at all.

[ZaphodBeeblebrox]

It is possible to have a planet with an atmosphere rich in oxygen and with little or no photosynthesis;

Most of the oxygen in our own atmosphere was not created by the plants we have on Earth today, so an Earth-like world could lose all its atmosphere and retain a high oxygen level for tens of millions of years.

Addiionally an atmosphere of a waterworld about the size of the Earth might have an atmosphere rich in oxygen; water vapour in the atmosphere could be split by photolysis, the hydrogen would excape, leaving the oxygen. Depending on what other components exist in the planet's atmosphere you might get a breathable mix with no life at all.

But ...

With Little or No, Chance of Replenishment.

Once you Breathe it, it's Gone ...

[Mellow]

Yup,

it's the replenishment I wonder about, thats why I refer to a factory. Interesting discussion though

Also, whilst I agree about the clips we see are not neccessarily representative of the whole planet, the discussion continues because other posters have suggested that that could be the case. ie: a whole planet of desert (Dune?)

I enjoyed reading Science of Discworld (Jack Cohen and Ian Stewart) a book full of up to the minute good science, and wonder if there's a bulleting board for "BadScience"?

[Swift]

It is possible to have a planet with an atmosphere rich in oxygen and with little or no photosynthesis;

Most of the oxygen in our own atmosphere was not created by the plants we have on Earth today, so an Earth-like world could lose all its atmosphere and retain a high oxygen level for tens of millions of years.
I don't think it would be tens of millions of years.
This (http://paos.colorado.edu/~fasullo/pjw_class/wksheet20_ans.html)website gives the residence time of oxygen in the atmosphere as 5500 years. Free oxygen (O2) is extremely reactive. If I remember correctly, the vast majority of the oxygen on the Earth is tied up in compounds, such as water, silica (SiO2, sand and silica minerals) or iron and other metal oxides.



Addiionally an atmosphere of a waterworld about the size of the Earth might have an atmosphere rich in oxygen; water vapour in the atmosphere could be split by photolysis, the hydrogen would excape, leaving the oxygen. Depending on what other components exist in the planet's atmosphere you might get a breathable mix with no life at all.

Why would the water vapor be split into oxygen and hydrogen? This is a pretty high energy reaction. You need about 1000C to thermally split water (reference (http://www.eere.energy.gov/hydrogenandfuelcells/production/basics.html)), or some sort of other means like electrochemical cells.

[eburacum45]

Where would the oxygen go? Your link is irrelevant to the actual amount of oxygen present in our atmosphere right now; if you burnt all the carbon in the biosphere it would reduce the oxygen level by no more than a couple of percent; the rest of the surface of the Earth is already oxidised by contact with an oxygen rich atmosphere.


and as far as splitting water vapour goes, ultraviolet light is plenty strong enough to split water vapour in a planet's atmosphere- especially if the local star is a little hotter and bluer than our own. UV photolysis had an important role in the dehydration of both Mars and Venus.

[AndrewGPaul]

Yup,

it's the replenishment I wonder about, thats why I refer to a factory. Interesting discussion though

Also, whilst I agree about the clips we see are not neccessarily representative of the whole planet, the discussion continues because other posters have suggested that that could be the case. ie: a whole planet of desert (Dune?)?

In the case of Arrakis, the biology of the Worms created the oxygen - it was exhaled by them, IIRC.

[Swift]

Where would the oxygen go? Your link is irrelevant to the actual amount of oxygen present in our atmosphere right now; if you burnt all the carbon in the biosphere it would reduce the oxygen level by no more than a couple of percent; the rest of the surface of the Earth is already oxidised by contact with an oxygen rich atmosphere.
I guess, though I don't have the data. I suppose it depends on if we are talking about a world where there was life and photosynthesis, which created an oxygen atmosphere, and then somehow died away, versus a world that never had photosynthesis. But I'll turn it around, where do you get a number like tens of millions of years? My gut feeling is, even if somehow you shutdown photosynthesis on Earth (big dust cloud?) that we would not have breathable amounts of oxygen for tens of millions of years. But I don't have the data.



and as far as splitting water vapour goes, ultraviolet light is plenty strong enough to split water vapour in a planet's atmosphere- especially if the local star is a little hotter and bluer than our own. UV photolysis had an important role in the dehydration of both Mars and Venus.
But for UV light to split water, you have to absorb the UV light, and water absorbs UV poorly scroll down for spectra (http://www.lsbu.ac.uk/water/vibrat.html). The normal way to do this as an "industrial" process is to have something like TiO2 absorb the UV and that drive the reaction to split the water. I say industrial in quotes, because no one has gotten this reaction to proceed at anything like commercial rates (I did research on this years ago).

Very high up in the atmosphere, UV does drive the O2 to O3 (ozone) reaction, but this would not drive the water splitting.

I'll admit I'm a little ignorant about the UV photolysis mechanism on Mars. But Mars seems to prove the point - the available oxygen all reacted with the solids on the surface (thus all the red iron oxide) and did not leave an oxygen atmosphere.

[snowcelt]

Swift. I do not think that ALL the O2 was absorbed by the planet. It seems to me that the O2 would have been absorbed over millions of years when the planet was still in a dynamic stage. When there was no medium left as a catalyst to absorb O2 the remaining O2 would have leaked of the planet over a relatively short amount of time.

[eburacum45]

I think the reason an abiotic oxygen atmosphere is expected on a waterworld is that the oxygen would have no land surface to oxidize;
a waterworld would have an ocean tens of kilometers thick, overlaying a layer of high pressure ice denser than water;
UV photolysis would split the water vapour in the upper atmosphere, and the hydrogen would split off;
http://www.geocities.com/alt_cosmos/evap.html
shows the process as it occured on Mars, but if we imagine a waterworld halfway between the mass of Mars and Earth, the O2 might find little to combine with and remain in the atmosphere.

It has been suggested that a planet with an abiotic nitrogen/oxygen atmosphere would eventually develop a NO atmosphere, producing nitric acid seas...

[The Supreme Canuck]

But then we'd have a lot of hydrogen in the atmosphere. Would it be breathable?
Why? Just because there is a layer of ice water doesn't mean that the atmosphere can't be a Nitrogen/Oxygen mix, especially when there are alges and planktons in the oceans. Are the levels of Hydrogen greater in the Artic or Antartic?

I was going on Humphrey's suggestion that breathable air could be created by splitting water molecules. I was also assuming an ice-ball planet - no open oceans. Just ice and snow.

Added: Whoah! Sorry about being a bit slow on the response.

[ZaphodBeeblebrox]

I think the reason an abiotic oxygen atmosphere is expected on a waterworld is that the oxygen would have no land surface to oxidize;
a waterworld would have an ocean tens of kilometers thick, overlaying a layer of high pressure ice denser than water;
UV photolysis would split the water vapour in the upper atmosphere, and the hydrogen would split off;
http://www.geocities.com/alt_cosmos/evap.html
shows the process as it occured on Mars, but if we imagine a waterworld halfway between the mass of Mars and Earth, the O2 might find little to combine with and remain in the atmosphere.

It has been suggested that a planet with an abiotic nitrogen/oxygen atmosphere would eventually develop a NO atmosphere, producing nitric acid seas...

Fun!

Sizzle ...

[Swift]

I think the reason an abiotic oxygen atmosphere is expected on a waterworld is that the oxygen would have no land surface to oxidize;
a waterworld would have an ocean tens of kilometers thick, overlaying a layer of high pressure ice denser than water;
UV photolysis would split the water vapour in the upper atmosphere, and the hydrogen would split off;
http://www.geocities.com/alt_cosmos/evap.html
shows the process as it occured on Mars, but if we imagine a waterworld halfway between the mass of Mars and Earth, the O2 might find little to combine with and remain in the atmosphere.

It has been suggested that a planet with an abiotic nitrogen/oxygen atmosphere would eventually develop a NO atmosphere, producing nitric acid seas...

Fun!

Sizzle ...
And that's why you shouldn't splashland your steel or aluminum spaceship on such an ocean. :wink:

[Chip]

In the 1966 Star Trek episode "The Man Trap" a member of the crew makes a reference to "Wrigley's Pleasure Planet." Imagine, a whole planet devoted to "pleasure." :wink:

[JonClarke]

Just a couple of quick comments on atmosphere, lithosphere, and ocean chemsitry. If all O2 production would magically stop it would indeed be rapidly consumed. For example most iron-bearing rocks are ferrous, not ferric. Exposure of fresh, ferrous rocks (mafic and ultramafic rocks in particular) by uplift and erosion allows ongoing weathering to take place. Furthermore, hydrothermal circulation of seawater through the ocean crust also pulls oxygen out of solution through alteration of the ferrous iron in the mafic and ultramafic rocks of that crust.

Nitric acid oceans are a charming idea, but again, once pH tends towards being too extreme rock buffering becomes significant. There is a reason why natural waters rarely have pH below 5 for any great area. Localised low pH does occur, but always related to point source effects such as sulphide oxidation. So the nitric acid is going to be quite dilute.

Even the acid ocean proponetents for Mars are not talking about pH below 5, as I recall. Coca-Cola has a pH of 2.5.

Getting back to the oxygen on a desert planet idea, didn't Frank Herbert have the sand worms as a major source of oxygen (or was it the sand plankton)?

Cheers

Jon

[Mellow]

I have to say, I love this BB.

I joined in some posts because I had a gut feeling that a desert planet or Ice planet couldn't replenish an atmosphere. (almost guilty of handwaving) and then people with much better subject knowledge than I join in and post, quality thinking, bravo friends, really appreciated.

Thanks

[eburacum45]

Just a couple of quick comments on atmosphere, lithosphere, and ocean chemsitry. If all O2 production would magically stop it would indeed be rapidly consumed. For example most iron-bearing rocks are ferrous, not ferric. Exposure of fresh, ferrous rocks (mafic and ultramafic rocks in particular) by uplift and erosion allows ongoing weathering to take place.
No, that can't be right;
consider the amount of oxygen in the air...
where did it come from?
How long has it been there?
How much of it has been 'produced' in the last hundred million years?
Remember there is 10e18kg of oxygen in the atmosphere, but only 10e16 carbon in the biosphere...
if it was that easy to get rid of, we would only have 10e16 kg of oxygen in the atmosphere.

[eburacum45]

In the 1966 Star Trek episode "The Man Trap" a member of the crew makes a reference to "Wrigley's Pleasure Planet." Imagine, a whole planet devoted to "pleasure." :wink:

Yes... for some reason that made me think of chewing gum at the time...

[Ilya]

In the 1966 Star Trek episode "The Man Trap" a member of the crew makes a reference to "Wrigley's Pleasure Planet." Imagine, a whole planet devoted to "pleasure." :wink:

Why not? Basically, it is a planet whose main industry is tourism/gambling/sex/recreation. In a Galaxy-scale economy, such "super Las Vegas" is entirely possible.

[ToSeek]

In the 1966 Star Trek episode "The Man Trap" a member of the crew makes a reference to "Wrigley's Pleasure Planet." Imagine, a whole planet devoted to "pleasure." :wink:

Why not? Basically, it is a planet whose main industry is tourism/gambling/sex/recreation. In a Galaxy-scale economy, such "super Las Vegas" is entirely possible.

We've got islands like that now....

[snowcelt]

[quote=Chip]In the 1966 Star Trek episode "The Man Trap" a member of the crew makes a reference to "Wrigley's Pleasure Planet." Imagine, a whole planet devoted to "pleasure." :wink:

Why not? Basically, it is a planet whose main industry is tourism/gambling/sex/recreation. In a Galaxy-scale economy, such "super Las Vegas" is entirely possible.

We've got islands like that now....[/quote

Great Briton and Ireland?

[Chip]

...We've got islands like that now....

Perhaps ToSeek is thinking of a Tahiti planet, which gets us back to the all tropical planet idea.

StarTrek of course also had those planets where the population was all of one frame of mind:
All logical.
All warlike.
All commercial.

And there was also that episode where the whole planet has underground factories with sensors that pop up and read your mind so as to create whatever you imagine. They get in trouble but eventually realize that its an amusement center for an advanced civilization to come and "play." (For "the more advanced the mind, the more the need for the simplicity of play.") 8)

[JonClarke]

Hi eburacum45

According to this web site: http://paos.colorado.edu/~fasullo/pjw_class/wksheet20_ans.html the residence time for O2 is 5500 years.

I said that is the oxidation of ferrous iron to ferric that consumes most of the oxygen, not the oxidation of carbon. Iron more common than carbon in the crust by two orders of magnitude. But don't worry, I missed the fact that someone else had already commented on the source of oxygen on Arrakis :lol:

Cheers

Jon

[eburacum45]

Yes; but that is not the length of time that the oxygen in our atmosphere would take to disappear.

By far the greatest amount of oxygen in our atmosphere comes from photosynthesis; this reaction occurs as a reduction of CO2 into carbohydrates and oxygen.
The mass of oxygen in the atmosphere is 10e18 kg;

the carbon in the biosphere is no more than 10e16kg.
photosynthesis of the current biosphere is responsible for no more than a couple of percent of the oxygen in the atmosphere; if all photosynthesis stopped today (say we put a big sunshade up like Mr Burns)
respiration would then remove that couple of percent, then stop. Once all the carbon in the biosphere is oxidised it cannot absorb any more.
After that we only have the slow oxidation of newly exposed rocks; I would stick my neck out and suggest that chemical oxidation would take hundreds of millions of years to remove the oxygen.

Where did all the rest of the oxygen come from?
It is fossil oxygen, produced by plants hundreds of millions of years ago;
the carbon side of the photosynthsis equation has been incorporated into the crust, not only as fossil fuels; a vast range of sedimentary rocks contain the balancing carbon; it would take billions of years for that carbon to become oxidised.

(added;)
Chemical oxidation of iron bearing rocks occurs all the time, whether there is a biosphere or not; if it was capable of removing the oxygen from our atmosphere it would already have done so.

[eburacum45]

As far as the 'residence time' goes, that is calculated by estimating the rate that oxygen enters the atmosphere, and as the oxygen level is constant, that also gives the rate at which it leaves the atmosphere;
both rates are almost completely set by the biosphere and photosynthesis.

this rate only applies to a system in steady state, and has no bearing on the length of time it would take to remove all the O2.

[John Dlugosz]

Hmm, yes I understand that, I'm just not overly convinced that lichen could produce enough breathable air of whatever composition.

I guess I'm thinking about the size of the "air factory" if you like. Perhaps my mistake is to assume you'd need a big "air factory" like the Algae in earth's oceans.

Incidentally, I love it when people call the rain forests the lungs of the earth or similar, nice bit of bad biology. Nobody thanks the oceans...

So, not a well thought out issue that I have, just a gut reaction to what I'm shown on television and film. There, desert planets are just miles and miles of sand. I don't recall seeing cacti or anything on Dune and Star Wars IV. Apologies to the fans if I'm incorrect in that... :D

Most of the life on Earth is microscopic. Perhaps on a planet with a more hostile environment it would stay that way longer than it did on Earth.

[JonClarke]

First of all the 5500 year residence time for O2 assumes that oxygen production ceases but oxygen consumption, much of it vi respiration does not. However, with this caveat that is how long it would take to delete the earth's oxygen. Calculating how long it would take to be depleted abiotically it rather more tricky. Especially as all numbers on global rates and cycles are all back of the envelope. However they should give us order of magnitude approximations.

OXIDATION OF ORGANIC CARBON

There is 3 X 10e15 kg of organic carbon in the global biomass and dissolved in water. Complete oxidation of that would consume 8 X 10e15 kg O2. The problem is we (or at least I) don't know the rate at which this occurs. Annual organic production is ~10e10 kg and 99.9% of this is recycled. However much of the recycling is biological. If we assume that 10% is non-biological oxidation we get destruction of 10e9 kg and consumption of 1.3 X 10e9 kg O2.

I think you are under estimate the efficiency of rock weathering and seafloor alteration in sequestering oxygen. For example:

TERRESTRIAL WEATHERING

The continental denudation (weathering) rate is 1.65 cubic kilometers/yr. Essentially all of this is of weathered material so represents a minimum terrestrial weathering rate. To calculate what this means in terms of oxidation of iron:

1.65 km3 X 2.7 (average density of continental crust) X 10e12 (kg per km3) = 4.46 X 10e12 kg per year

Continental crust averages 3% FeO = 1.34 X 10e11 kg. Weathering this to Fe2O3 consumes 1.5 x 10e10 kg O2

OCEANIC ALTERATION

Top 5 km of oceanic crust accretes at 9.0 km3/yr at spreading centres. It is also destroyed at this rate though subduction

9.0 X 3.0 = 27.0 X 10e12 kg per year.

Ocean crust averages 10% FeO = 2.7 X 10e12 kg. If 10% is oxidised (which is reasonable given the extent of hydrothermal alteration) this means that 2.7 X 10e11 kg FeO alters to Fe2O3, consuming 3 X 10e10 kg 02

TOTAL

Therefore every year 4.5 X 10e10 kg O2 is consumed by rock weathering alone. Plus 1.3 10e9 kg through oxidation of carbon (an order of magnitude less). Say approximately 5 X 10e10. If the atmospheric repository is 10e18, this would be consumed in 20 My. Four orders of magnitude longer than if respiration continued unabated, but an order of magnitude less than your estimate of 100's of My. Twenty My is not long, geologically speaking - less than 0.5% of the history of the earth.

Cheers

Jon

[eburacum45]

Oh, well; my first estimate seems to be more accurate.

Nevertheless; if chemical oxidation of rocks was as rapid as your estimates, the oxygen in the air which was placed there during the Carboniferous would have disappeared by now; if the only route by which oxygen enters the atmosphere is via photosynthesis, then we would only have oxygen equal to or slightly above the balancing carbon in the biosphere.

Instead we have two orders of magnitude more oxygen in the atmosphere than there is carbon in the biosphere; this suggests to me that the removal of oxygen by the lithosphere is very slow indeed.

[JonClarke]

eburacum45

The removal of oxygen from the atmosphere by weathering is slow compared to its removal by respiration. Hence the 5000 year residence time with a biosphere as opposed to 20 My without. But it is still short compared to the history of the planet. the landscape I live in goes back 20 My, and the rocks my house is built on at 20 times older than that. And it is less than 0.5% of the history of the earth.

Cheers

Jon

[eburacum45]

My objective was to dispel the urban myth that our present day biosphere is responsible for the oxygen in our atmosphere;
neither the present day forests nor the present day ocean phytoplankton are sufficient to produce the oxygen in our atmosphere, and if photosynthesis stopped, oxygen would remain for millions upon millions of years.

I expect that when we are able to examine terrestrial worlds in detail we may find a small but significant class of planets with oxygen atmospheres but no life-

this does not mean the atmosphere would be breathable, as the CO2 level or other contaminants may prevent that.

[JonClarke]

The earth has had only one biosphere, which has evolved over the past 3.5 to 4 Gy. I don't think there can be any reasonable doubt whatsoever that the oxygen in the earth's atmosphere is the result of that biosphere. Atmospheric O2 and bisophere diversity increase in tandem from the Late Archaean onwards. UV photodisassociation of CO2 and H20 contributes no more than 1% of PAL (present atmospheric level), 0.2% in other words. All potential sources of gases are reduced, the solar nebula, the earth's mantle, comets and meteorites. There just are no abiogenic sources of significant O2 and the minscule amount from photodisassociation is rapidly consumed by mineral weathering which is why it is maintained at such low levels in the atmospheres of Venus and Mars.

Cheers


Jon

[eburacum45]

Yes quite; but it is not the biosphere we have today which has produced the oxygen in our atmosphere, but the biospheres of the past; far from being one biosphere, more than 90% of the carbon in our archaic biospheres is now buried deep underground...
in order to reduce the oxygen in our current atmosphere you would need to dig up all the buried carbon which used to be in our archaic biosphere, all ~10e18 tonnes of it, and add it to the ~10e16 tonnes in our current biosphere.
Only then then could you recreate our prebiotic CO2 atmosphere.

Until you do that the oxygen stays, except for the slow process of chemical oxidation in newly exposed rocks (which I think is less rapid than your estimate).

[JonClarke]

I confess don't see your point.

We agree that there are no alternate sources of oxygen other than the biosphere. Irrespective of whether it was produced in the past or present, oxygen is the result of photosynthesis. Eliminate the biophere and there is no more oyygen produced, what is there will be consumed by weathering of surface organic matter and rocks

Why do you persist in ignoring rock weathering? Please show me the numbers why you think I have overestimated its importance. If anything I have underestimated its importance as I have not factored in the weathering of buried carbon.

Incidently there is no evidence that the earth has had a CO2 atmosphere in the last 3.5 billion years. Geochemical processes mediated by the hydrophere are quite effective in sequesting CO2 in rock as carbonate.

Cheers

Jon

[JonnyWishbone]

Getting back to the oxygen on a desert planet idea, didn't Frank Herbert have the sand worms as a major source of oxygen (or was it the sand plankton)?

Cheers

Jon

Both -- I think it's the appendix to the original Dune that makes it clear that the sand plankton (which are the primary foodstuff of the Sandworms) provide most of the oxygen in the atmosphere of Arrakis, though the Sandworms do produce some, along with all that tasty spice.

TTFN, (also) Jon

[eburacum45]

It is quite simple;
I agree that there is almost no oxygen produced by photodissociation in our atmosphere-
estimates of one percent seem correct.
So where did it come from? Almost all the oxygen in the atmosphere has been created by photosynthesis from carbon dioxide;

although the atmosphere has never been predominantly CO2, this is where the oxygen originates from. How else did 10e18 tonnes of oxygen enter our atmosphere?
Almost all the oxygen in our atmosphere was at one time CO2.

Every two atoms of oxygen now present in our atmosphere (apart from the one percent created by photodissociation) were once combined with one atom of carbon;
(atomic weight of oxygen ~16, carbon is ~12 so by weight we have 32 tonnes of oxygen partnered by 12 tonnes of carbon.)
say one tonne of carbon per 3 tonnes of oxygen.

But there is less than 10e16 tonnes of carbon in the biosphere...


that leaves (10e18 -10e16)/3 tonnes of carbon missing.
we can approximate this as 10e17 tonnes;

all of which has been incorporated into sedimentary rocks over the last 3.5 billion years since the evolution of photosynthesis.

As this carbon is removed from contact with the atmosphere it cannot react with it; the oxygen long ago reached a steady state with the rocky surface of the world, so that the oxygen we now have in our atmosphere wa created by photosynthesis hundreds of millions of years ago.

The consequence of this is that the biosphere cannot remove the oxygen fom the atmosphere; there is not enough carbon in the biosphere to do this.
But if oxygen is being constantly removed by chemical oxidation of rocks why has the oxygen in the atmosphere not all disappeared?

New oxygen reenters the atmosphere from the lithosphere in the form of carbon dioxide outgassing; photosynthesis separates this CO2 into oxygen and carbon-
but as the mass of the biosphere does not increase on average, the same amount of carbon that enters the biosphere from volcanic CO2 must leave it and become incorporated into rocks.

The amount of oxygen entering the atmosphere via CO2 outgassing must equal the loss of oxygen leaving the atmosphere via oxidation; or we would have lost our oxygen atmosphere long ago.

Now remove photosynthesis and respiration will start to combine organic compounds with oxygen, which will quickly convert the biosphere into CO2; this process would take much less time than 500 years.That stll leaves more than 10e17 tonnes of oxygen in the air.

This leaves chemical weathering; this will remove the oxygen at a much slower rate; your estimates say 20my, and you might be right; the oxygen entering the lithosphere will continue to be balanced by CO2 outgassing, but now there is no photosynthesis to split the oxygen off.
CO2 will get incorporated into sedimentary rocks so we will end up with an atmosphere mostly consisting of nitrogen.

One way to estimate the rate of chemical oxidation is to find out how much C02 is released by volcanic outgassing each year; as this is the only way oxygen reenters the atmosphere from the lithosphere, this should match the rate of oxidation by chemical weathering.

Volcanic outgassing of CO2 is between 10e8 and 10e9 tonnes per year;
this means that between 10e8 and 10e9 tonnes (say 10e9) of oxygen must be removed into the lithosphere by oxidation each year (any more and the atmosphere would lose oxygen)...

to get rid of the unbalanced 10e17 tonnes of oxygen which would be left behind by the complete oxidation of our current biosphere, this removal of 10e9 tonnes of oxygen per year would take a hundred million years;


rough, but only one order of magnitude different to your estimate...

[JonClarke]

I think we are in agreement over many points, so following are just the remaining areas of significant disagreement.

”although the atmosphere has never been predominantly CO2, this is where the oxygen originates from. How else did 10e18 tonnes of oxygen enter our atmosphere? Almost all the oxygen in our atmosphere was at one time CO2.”

Whoa there! A few posts back you said it was 10e18 kg, not tones. Please be consistent with units.

”As this carbon is removed from contact with the atmosphere it cannot react with it; the oxygen long ago reached a steady state with the rocky surface of the world, so that the oxygen we now have in our atmosphere wa created by photosynthesis hundreds of millions of years ago.”

There are three issues:

The buried carbon can and does react with the atmosphere through uplift, weathering and erosion. This is called the rock cycle. Some buried carbon is recycled through subduction and volcanic degassing. Some is oxidized through groundwater flow. It is not correct that once carbon is buried in sedimentary rocks cannot interact with oxygen. It is a rough approximation, but not an accurate one

The surface of the earth is not in equilibrium with oxygen which is why it weathers. Because of the rock cycle, which is driven by plate tectonics, there is a constant supply of fresh rock to undergone weathering, both on the sea floor and on the continents. It is incorrect to say that the lithosphere is in a steady state with the atmosphere. Many sedimentary rocks and most igneous rocks are reduced.

The residence time for oxygen is (depending on which source you read) of the order of 2000-5000 years. In hundreds of millions of years the oxygen in the atmosphere will have cycled through the biosphere hundreds of thousands of times. Although the atmosphere has been significantly oxygenated for at least 1.8 billion years we can’t say that the oxygen in this atmosphere is anything like this old. The oxygen in the earth’s atmosphere is in dynamic equilibrium. In such cases it is meaningless to talk about “age”. It is like a lake with an inlet and an outlet. The lake basin may be thousands of years old but the residence time may be only a few months or years.

”The consequence of this is that the biosphere cannot remove the oxygen from the atmosphere; there is not enough carbon in the biosphere to do this.”

Agreed – that is why if the biosphere were to shut down the surplus would be removed by weathering

”But if oxygen is being constantly removed by chemical oxidation of rocks why has the oxygen in the atmosphere not all disappeared?”

Two reasons, first because the rate is trivial compared to the rate of biological removal and production and secondly because the system is in dynamic equilibrium.

”New oxygen reenters the atmosphere from the lithosphere in the form of carbon dioxide outgassing; photosynthesis separates this CO2 into oxygen and carbon-
but as the mass of the biosphere does not increase on average, the same amount of carbon that enters the biosphere from volcanic CO2 must leave it and become incorporated into rocks.”

Why do you say this is new oxygen? Most volcanic CO2 is from breakdown of carbonate not buried organic matter. There is 10X as much carbon locked up as carbonate in the crust than there is as organic carbon. Release and update of oxygen is not a factor in the carbonate cycle, which is controlled by carbonate precipitation during weathering, sedimentation, diagenesis, and hydrothermal alteration.

”The amount of oxygen entering the atmosphere via CO2 outgassing must equal the loss of oxygen leaving the atmosphere via oxidation; or we would have lost our oxygen atmosphere long ago.”

As noted CO2 outgassing is related to the carbonate cycle, not the oxygen cycle. So this is irrelevant

”Now remove photosynthesis and respiration will start to combine organic compounds with oxygen, which will quickly convert the biosphere into CO2; this process would take much less time than 500 years.That stll leaves more than 10e17 tonnes of oxygen in the air.”

Why much less than 500 years? Most organic matter is broken down by biological action- respiration in other words. Without respiration it will occur at a much slower rate. Even with biologic activity, some organic matter lasts on the surface for thousands of years before it is buried.


”One way to estimate the rate of chemical oxidation is to find out how much C02 is released by volcanic outgassing each year; as this is the only way oxygen reenters the atmosphere from the lithosphere, this should match the rate of oxidation by chemical weathering.

Volcanic outgassing of CO2 is between 10e8 and 10e9 tonnes per year;
this means that between 10e8 and 10e9 tonnes (say 10e9) of oxygen must be removed into the lithosphere by oxidation each year (any more and the atmosphere would lose oxygen)...”

Again, the oxygen in most of the CO2 in volcanic gases has not been fixed by respiration, but is cycled through carbonates, which are oxygen neutral.

to get rid of the unbalanced 10e17 tonnes of oxygen which would be left behind by the complete oxidation of our current biosphere, this removal of 10e9 tonnes of oxygen per year would take a hundred million years;

rough, but only one order of magnitude different to your estimate...

if we get to an order of magnitude then we are essentially in agreement This is good, but, as in this case, your calculation is based on the carbonate cycle which is irrelevant to the oxygen cycle, I suspect this is coincidence.

Cheers

Jon

[eburacum45]

Yes, you are right; it probably is coincidence. I was trying to find a route out of the lithosphere for oxygen, as the oxygen cycle must be balanced;
the only route that oxygen can take out of the lithosphere that I am aware of is with the carbon dioxide (if you know of another route for oxygen to leave the lithosphere I would be interested).

I was hoping to find a maximum value for this, which would balance the rate of oxidation;
but as I switched from kg to tonnes accidentally, I got the value wrong.

Outgassing of CO2 is therefore 10e12 kg per year- this represents a maximum oxidation rate of 10e12kg (although the oxidation figure will in fact be less, as the recycling of oxygen will be a fraction of the recycling of CO2 by this route)...
if all the oxygen released as CO2 balances the oxidation of the lithosphere,(which it does not) then it would take only a hundred thousand years for lithospheric oxidation to remove the oxygen component left behind after the dead biosphere ceases to oxidise.

This means that the rate of oxidation of the lithosphere could be relatively high, and can't be determined from CO2 outgassing, although this gives a tentative maximum value.
I am still reasonably sure that oxidation is slow, simply because the massive amount of oxygen in the atmosphere is maintained by an insignificantly small biosphere.

What is certain is that respiration could not remove the oxygen in the atmosphere, and fermentation and decay would not even manage to oxidise the whole biosphere (as you pointed out, some organic matter will remain to be buried).
So the present biosphere maintains the dynamic equilibrium of the atmosphere, but has not itself produced the oxygen; every two atoms of oxygen in the air is balanced by an atom of carbon, and by far the greatest part of that balancing carbon is buried in sediments.

Added;

The oxygen cycle is rather poorly depicted in educational material, such as this site;
http://paos.colorado.edu/~fasullo/pjw_class/images/oxygencycle.gif
this presentation ignores non-carbon lithospheric weathering, although it does show the correct ratios between atmospheric oxygen and the biosphere;

later in the same presentation
http://paos.colorado.edu/~fasullo/pjw_class/oxygencycle6.html
it states that weathering and respiration will deplete the atmosphereic oxygen in 5000 years, which cannot be the case.

[eburacum45]

One oxygen cycle that might be relatively common out there among the Terrestrial planets is this one;
the Banded Iron regime;
http://jersey.uoregon.edu/~mstrick/RogueComCollege/RCC_Lectures/Banded_Iron.html
oxygen seems to have been been toxic to many early photosynthetic organisms, and it would become an unwanted pollutant, killing much of the biosphere periodically;
the banded iron regime lasted for 800 million years (according to this link).

[eburacum45]

I suppose I should have dug this stuff out long ago- sorry; apologies for the thread hijack, by the way, but I find this stuff interesting- soon we will be detecting terrestrial planets, and I only want to remind people that the detection of free oxygen does not always mean life. Oxygen has been discovered in the comet-like tail of the hot jupiter planet HD 209458b; oxygen will almost certainly be found elsewhere.

I have found some figures for oxygen sequestration in my old geology textbook (Holmes, 1965)(it is thirty years since I was at college- I only use Holmes for worldbuilding these days)


According to Wickmann, cited by Holmes, there has been a total of
8437 x10e15 kg oxygen produced by photosynthesis over the history of the biosphere;

1109 x10e15 kg oxygen in the current atmosphere
11 x10e15 kg oxygen dissolved in the oceans
1270 x10e15 kg has been lost by the oxidation of iron minerals
3719 x10e15 kg lost to the oxidation of sulphur
2327 x10e15 kg unaccounted for- probably lost to the suspected oxidation of H2 and CO


This is balanced by 91 x10e15 kg fossil fuels
3081 x10e15 kg other buried, reduced carbon.
3 x10e15 kg in biosphere (using your own figure)

So seven times at much oxygen has been sequestrated by chemical weathering over the history of the biosphere as remains in the atmosphere- it does not seem to be a complete cycle at all;

In other words, if we ignore oxygen which has been recycled, chemical weathering has removed more than seven times the equivalent of our present oxygen atmosphere over the history of our biosphere; more than one atmosphere per five hundred million years.

Chemical weathering is a respectable force, and seems to be at least partly unbalanced by emissions of oxygen from the crust.

[JonClarke]

Holmes is a giant and still well worth reading despite the passage of time.

The following web site is interesting as well, although the writer insists on using moles. Darn chemists! :-?

http://ethomas.web.wesleyan.edu/wescourses/2004s/ees227/01/227lect16.htm

Cheers

Jon

[tracer]

The following web site is interesting as well, although the writer insists on using moles. Darn chemists! :-?
In one thesis/dissertation my astro professor told me about, the author listed the amount of alcohol present in an interstellar nebula in units of shot glasses.

When told that a shot glass wasn't an S.I. unit, the author countered by saying, "Sure it is! It's a barn-parsec."

[eburacum45]

The mention of high oxygen values during the carbonioferous is interesting; in my local museum there is a fossil of a giant Carboniferous spider (Megarachne) the size of a small cat.

A high O2 content would make the respiration of such large land arthropods less difficult to explain- but it also would have increase the risk of forest fires, and increased combustion would decrease the O2 level. Perhap this high O2 level was cyclic, rather than long term... the arthropods might have had a range of maximum sizes dependent of the oxygen level.