Venus' Crust Heals Too Fast For Plate Tectonics

An anonymous reader writes in with an interesting look at how important plate tectonics may be to life and why the crust on Venus works differently than it does on Earth. "Without plate tectonics, carbon would build up in the atmosphere. Venus, which does not have tectonics, shows the results: an atmosphere that is 96 percent carbon dioxide. It's toxic. Yet Venus is about the same size and composition as our planet, so why doesn't it have plate tectonics? Some researchers made a model to explore how Earth initiated plate movements, and these same researchers made one model of its neighbor for comparison. A 1.5-billion-year-old Earth and a similarly aged Venus were modeled as a hot, mushy material made of tiny particles of rock. The model uses physics at the one-millimeter rock grain scale to explain how the whole planet behaves. According to David Bercovici, a geophysicist at Yale who was an author on the paper, the model also shows how plate tectonics emerged on Earth but not on her twin."

Comments

Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

Is it very surprising that a completely different orbit around the sun and different composition result in different crust phenomena?

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

Is it very surprising that a completely different orbit around the sun and different composition result in different crust phenomena?

No, but that's not what the article is about either. The article is saying that they've found a causal mechanism linking the known differences in venus's orbit/formation to the observed lack of tectonic plates. And more importantly they have a model that may allow them to predict what planets would/would not have tectonic plates based on their temperature.

Re:Venus isn't Earth's "twin" really at all.

[rubycodez]

you are mistaken, the composition of Venus rock from surface on down is nearly identical to Earth.

Re:Venus isn't Earth's "twin" really at all.

[darthlurker]

There's a big difference between Earth and Venus.

Later doesn't have an over-sized moon.

Re:Venus isn't Earth's "twin" really at all.

[mmell]

Currently theorized to have resulted from an impact so severe that it nearly shattered the planet, an impact so severe that the entire surface of the planet was blasted loose and redeposited on the surface.

Re:Venus isn't Earth's "twin" really at all.

[NatasRevol]

blasted loose, cooled, and redeposited on the surface.

Hmmm. that might make some nice big rocky plates.

Re:Venus isn't Earth's "twin" really at all.

[VernonNemitz]

I think the authors of the paper have overlooked something. It has been discovered that if we pump water into the ground along a fault line, we can literally lubricate the fault and help the plates slide past each other. (Side note: sounds like a good way to prevent major earthquakes, but nobody wants to be responsible for causing the initial quakes associated with unlocking long-locked plates. The problem with that attitude is, those quakes are eventually going to happen anyway, except they will be bigger and more catastrophic then, than if deliberately caused now.)

Anyway, on Earth we have lots of water, including water deep underground, presumably doing SOME assisting of tectonic plate motion. Meanwhile, on Venus it has always been too hot for much water to percolate deep underground....

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

I think the authors of the paper have overlooked something. It has been discovered that if we pump water into the ground along a fault line, we can literally lubricate the fault and help the plates slide past each other. (Side note: sounds like a good way to prevent major earthquakes, but nobody wants to be responsible for causing the initial quakes associated with unlocking long-locked plates. The problem with that attitude is, those quakes are eventually going to happen anyway, except they will be bigger and more catastrophic then, than if deliberately caused now.)

Next your going say something crazy like the steam generated by lubricating these tectonics could be used to generate power of the electrical kind. Some fantasy world you live in.

Re:Venus isn't Earth's "twin" really at all.

[FatdogHaiku]

There's a big difference between Earth and Venus.

Later doesn't have an over-sized moon.

That adds a lot of stress. Then pile on 1.3 billion cubic kilometres of water that tends to try to follow the moon around...
1,400,000,000,000,000,000 metric tons sloshing around would put cracks in pretty much anything.

Re:Venus isn't Earth's "twin" really at all.

[Will.Woodhull]

Is it surprising that there is a difference in the behavioral history of a single planet and a similar planet that happens to be part of a binary planet system?

Hint: Venus does not have tides; has never had tides. Earth tides were a lot larger when Earth was young and the Moon was closer. They are still large enough to put a significant do-si-do waggle in the Earth's orbit about the Sun. Despite what dumb-ass astronomer conventions might say, when a satellite is so large that it deflects its primary from its orbit by 4,000 miles, you have a binary planet.

Why do so many Earth "scientists" fail to see that you cannot talk sensibly about Earth's mechanics without acknowledging the Moon's influence? Of course there is going to be a difference between the pot that sits on the stove undisturbed, and the one that is constantly stirred.

</rant>

Re:Venus isn't Earth's "twin" really at all.

[able1234au]

which "dumb-ass" scientists that do not influence the impact of the moon on the earth are you talking about?

The Moon is considered a moon as the barycentre is within the Earth. Pluto on the other hand has its barycentre outside of it, though in its case we usually refer to it as a Dwarf planet rather than Dward binary. ...or am i missing something?

Re:Venus isn't Earth's "twin" really at all.

[Will.Woodhull]

No, you have not missed anything. You are parroting the "logic" of the Committee for Small Body Nomenclature of the International Astronomical Union. This is a true committee of fifteen members whose job it has been to decide on definitions of words. There was and is no science here. Nor was there any logic based on science; the logic was that of taxonomy: making pigeonholes to classify stuff. Nor was logic used in making the final determinations; what the pigeonholes were to be called was decided by vote. It was a "let's make new words" party, having nothing to do with astronomy, geology, or selenology. (See? It is both easy and fun to add words to the pseudoscientific jargon. Even scientists can do it!)

The Moon is considered a moon as the barycentre is within the Earth.

The barycenter of the Earth-Moon binary system (and that is a legitimate phrase) is always 1,000 miles below the lithosphere of the Earth, and 3,000 miles above the Earth's core. Quito, Equador, is a city on the equator. When there is a lunar eclipse on either the Spring or Autumn equinox at Quito, an interplanetary voyager arriving from Mars would find that Quito was 1,500 miles closer to the Sun than usual, but 12 hours earlier or later it was almost 1,500 miles further from the Sun than the navigator's first order approximation*. The communications officer of that interplanerary ship had better take into account the way the Earth spins about the barycenter of the binary system if he is to stay in laser beam contact with the Quito space port.

More significantly over the Earth's history is that its rotation around the barycenter raises tides. Not just the noticeable ones in the hydrophere, but large ones in the various layers of the atmosphere, and smaller, but significant, ones in the lithosphere. Geology has yet to develop an effective model on how the tidal strains on the lithosphere affect plate tectonics. But there can be little question that significant tidal forces are at work, alternately stretching and compressing faults.

In retrospect, what this august body of astronomers should probably have done is given their naming problem over to the experts who have recognized degrees in the appropriate field of study: these kinds of taxonomic decisions are better left to the linguists and other language experts. There are probably very few astronomers who have done any study of language arts at all. No wonder they bungled the thing so badly. They probably did not even know they were not doing astronomy any more. *

I would not mind having someone check my geometry here. I think the difference is actually 3,000 miles (displacement of the Earth's center from the barycenter) but I'm going with the more conservative number.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

Venus has tides from the Sun. For comparison, Earth's tidal acceleration at its surface from the Moon is a little over twice that of the tidal acceleration caused by the Sun. The tidal acceleration caused by the Sun on Venus is three times that of the solar tides on Earth, giving a larger stress on Venus than Earth gets from the moon. The only big difference is that the rotation of Venus is a lot slower.

Re:Venus isn't Earth's "twin" really at all.

[able1234au]

Well you do need a naming system and Planet is a useful naming system. What is evil about that? There are only 8 planets so you don't really need to subdivide them more. And if the earth-moon is a binary then what are Mars, Jupiter, Saturn, Uranus and Neptune? Pluto on the hand was relabelled by that evil committee not because it is also a binary, quaternary or whatever, simply because there are potentially thousands of dwarf planets, so calling them planets was not useful. That is usually the big complaint about that committee. I hadn't heard that people were unhappy about the Moon's status.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

Well, to start with, Earth is from Mars. And Venus is from Venus, you insensitive clod!

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

2040: Anyone who thinks "The Moon" is a moon is considered backwards and uneducated. English is an evolving language after all.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

The tides actually run ahead of the moon. which causes it to slow down and move further and further away. Fortunately the process is slow enough that the earth will be destroyed before the moon leaves its orbit.

Re:Venus isn't Earth's "twin" really at all.

[Will.Woodhull]

The barycenter of any planet and the Sun is far outside the planet's surface. Excepting Jupiter, whose barycenter with the Sun is approximately coincident with the Sun's surface, the barycenters are all deep within the Sun.

This means that the solar induced tides, no matter what their strength might be, do not perturb the planet's orbit. Nor do they distort the planet's shape to the degree that lunar tides distort the Earth's shape (and significantly perturb its solar orbit).

The study of geologic processes on Earth will continue to be significantly incomplete until it is recognized that the Earth and Moon function as a binary planet. Not as bodies that can be understood in isolation.

One would think that the International Astronomy Union and other professional organizations of astronomers would recognize this, but-- alas-- their heads appear to be too full of empty space to concern themselves with what is going on beneath their feet.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

You seem rather bitter about the IAU, and drag it back up in response to a post that had nothing to do with them or their definition...

Regardless of the position of the barycenter, the effects of the tidal force in terms of changed shape is directly proportional to the tidal acceleration and force. You can see this clearly with Earth's water tides, where the effect of the Sun is half that of the Moon, in proportion to the tidal acceleration. If there were no Moon around Earth, the Earth would still have easily noticeable tides, just about a third of the current peak size and much more regular in size. It has proportionately the same effects on the lithosphere, and likewise will have larger effects on Venus since tidal acceleration scales with the inverse cube of distance. There is plenty of academic work on the effects of the tide on things other than the oceans, including the shape of Earth and its atmosphere too, none of which is being held back by nomenclature.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

I don't think the post you were responding to was about the intensity of the tidal influence. The way I read it, he was talking about the place where the tidal forces are in balance being removed from the center of the planet to a location 2/3rds (3/4ths?) the distance from the center to the surface. I can see where that would probably affect the internal mechanics of the planet.

I think it is a valid point that astronomers are more involved in physics, etc, than they are in language. And trying to develop a set of categories, presumably for the purpose of making astronomy more clear to non-astronomers (like maybe geologists and biologists), has more to do with language skills than with the things astronomers study. Maybe they should have farmed out the work to some English majors. Maybe that would have the confusions and arguments of the last few years.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

The way I read it, he was talking about the place where the tidal forces are in balance being removed from the center of the planet to a location 2/3rds (3/4ths?)

What do you mean by "in balance"? There isn't anything particularly special about the barycenter when it comes to tidal forces, especially when you have tidal forces from more than two objects, and the only place the tidal force could be balanced by gravity would be within a meter of the center of the Earth (not barycenter) since it is very week compared to Earth's gravity. There is still a gradient in forces at the barycenter, which only varies by a couple parts per million across the Earth.

And trying to develop a set of categories, presumably for the purpose of making astronomy more clear to non-astronomers (like maybe geologists and biologists), has more to do with language skills than with the things astronomers study.

Except that is not the reason such categories were created. They were created for the purpose of communicating between astronomers, not for communicating to non-astronomers.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

. Despite what dumb-ass astronomer conventions might say, when a satellite is so large that it deflects its primary from its orbit by 4,000 miles, you have a binary planet.

All moons perturb their parent body's orbit. What is your arbitrary cutoff then? 4000 miles? Some number of kilometers? Half the radius of the surface? At least instead of picking an arbitrary number, some people want to go with a barycenter above the surface, although that has its own issues (very far away small objects, orbits that have the barycenter moving in and out of a body). Just exclaiming "Charon deflects Pluto only by 1200 miles in its orbit," or, "Titan deflects Saturn in its orbit by over 300 miles" seems kind of disingenuously throwing out large numbers.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

The way I read it, he was talking about the place where the tidal forces are in balance being removed from the center of the planet to a location 2/3rds (3/4ths?) the distance from the center to the surface. I can see where that would probably affect the internal mechanics of the planet.

Then this would be a fundamental misunderstanding of how tides work, something that is covered in an intro level text book on geophysics despite someone trying to claim geologists don't know about it.

Re:Venus isn't Earth's "twin" really at all.

[gzuckier]

But.... isn't Venus warmer because of the excess CO2, which is the result of lack of plate tectonics, which these guys say is the result of Venus being warmer? Who lit the fuse?

Re:Venus isn't Earth's "twin" really at all.

[gzuckier]

Good point. Tidal forces pull the crust up and down. On the other hand, this might be construed as heating it, which would be anti-tectonic.

Re:Venus isn't Earth's "twin" really at all.

[gzuckier]

But the pot which is NOT stirred is the one that will build up layers of floating junk on top, earthstyle.

Re:Venus isn't Earth's "twin" really at all.

[RockDoctor]

The amount of water injected into the mantle by subduction is sufficient to have a major effect on the mantle's stiffness. Without that water, plate tectonics is likely to stop considerably sooner than otherwise as the Earth cools.

Re:Venus isn't Earth's "twin" really at all.

[RockDoctor]

To segregate low-density material to the surface you need to have mass movement. Without external stirring, then you'll need to have internal stirring, which seems to be achieved with convection as a result of self-heating by radioactive decay in the mantle. The resulting movement results in the accumulation of low-density material at the surface and high density material at the core-mantle boundary.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

And trying to develop a set of categories, presumably for the purpose of making astronomy more clear to non-astronomers (like maybe geologists and biologists), has more to do with language skills than with the things astronomers study.

Except that is not the reason such categories were created. They were created for the purpose of communicating between astronomers, not for communicating to non-astronomers.

Well if astronomy has nothing of value to communicate outside its domain, then I guess that is ok. Once things were different, what with Kepler and Galileo and those guys, but now astronomy is just one big circle jerk among the telescope boys, huh?

Every member of the IAU should be ashamed for letting this total fuck-up in the use of language be done in their name.

Re:Venus isn't Earth's "twin" really at all.

[Anonymous Coward]

Because a committee deciding what jargon to recommend for use in a field is equivalent to having "nothing of value to communicate outside its domain"? After all, astronomy has a different definition of metal than chemistry, so of course there must never have been any overlap or exchange of work between those two fields... And I guess every other field takes understanding by public as their top priority when defining jargon, instead of precision or usefulness within the field, like IUPAC who have never defined or named things that different from common names...

Carbon dioxide is *NOT* toxic.

[Anonymous Coward]

Hundreds of millions of plants would challenge the notion that carbon dioxide is toxic.

Re:Carbon dioxide is *NOT* toxic.

[Anonymous Coward]

It tends to get a bit inhospitable when it's at a temperature of 737K and about 9.2 MPa of pressure (92 times what we have here), though...

Re:Carbon dioxide is *NOT* toxic.

[LordLimecat]

Amanita phalloides (Deathcap mushrooms) are NOT toxic.

Hundreds of thousands of rabbits would challenge the notion that it is toxic.

Re:Carbon dioxide is *NOT* toxic.

[Eunuchswear]

Are you a plant?

Re:Carbon dioxide is *NOT* toxic.

[arfonrg]

Wait, so it's NOT the lack of tectonics that prevents life on Venus but this "737K @ 9.2MPa" thing?

Re:Carbon dioxide is *NOT* toxic.

[Anonymous Coward]

Um, are you stupid, very stupid, extremely stupid or full-on inbred retarded? Oxygen isn't toxic either I guess, except at 100% concentrations... Idiot.

Re:Carbon dioxide is *NOT* toxic.

[Anonymous Coward]

At sufficiently low doses, nothing is toxic. At sufficiently high doses, everything is toxic.

Did you know you can (and people do every year) die from water toxicity?

Re:Carbon dioxide is *NOT* toxic.

[mmell]

Well, yes - but that

"737K @ 9.2MPa" thing?

might theoretically have been caused by the lack of plate tectonics.

Re:Carbon dioxide is *NOT* toxic.

[Anonymous Coward]

Well, yes - but that

"737K @ 9.2MPa" thing?

might theoretically have been caused by the lack of plate tectonics.

RTFA.

The starting point was the heat on Venus. That's what made the Venusian crust softer, thus preventing the creation of tectonic plates.

Re:Carbon dioxide is *NOT* toxic.

[mmell]

Badly worded on my part.

I was trying to express the idea that being closer to the Sun might not be the only factor involved. I personally suspect that it's the primary cause (and might be enough even if all other conditions were identical on Earth and Venus), but TFA is only positing a theory that there are other factors contributing to the differences we see.

Re:Carbon dioxide is *NOT* toxic.

[Anonymous Coward]

The real question is why venus has such a thick atmosphere. If you compare the temperature at the same pressures as earth troposphere it is nearly exactly as would be predicted due to being closer to the sun. Isn't mars supposed to have lost its atmosphere due to lack of a magnetic field? But venus also has no magnetic field and has a much thicker atmosphere.

Re:Carbon dioxide is *NOT* toxic.

[LifesABeach]

Are there mountains on Venus?

Re:Carbon dioxide is *NOT* toxic.

[mmell]

Mountains and volcanos. Venus most certainly is subject to geologic forces; but current theories and observations do not indicate the presence of geologic plates - therefore, no plate tectonics. Venus' crust appears to be a single, contiguous solid whole, not the fractured group of mechanically separate massive plates found here in Earth.

Re:Carbon dioxide is *NOT* toxic.

[arth1]

Are there mountains on Venus?

Through first hand experience, I can verify the abundance of Venus Mons.

Re:Carbon dioxide is *NOT* toxic.

[Anonymous Coward]

As the proverb goes, it's the dosage that does the damage.

Re:Carbon dioxide is *NOT* toxic.

[RockDoctor]

As Paracelsus pointed out in the 16th (15th?) century, it's the dose that makes the poison.

Re:Carbon dioxide is *NOT* toxic.

[RockDoctor]

The headline (strapline? whatever) picture in TFA is a radar-derived depiction of one of the larger mountains on Venus. I forget the name, unfortunately. (Wikipedia and my memory tells me that it's Maxwell Montes, which is 11km above the average level of the surface, making Venus somewhat more irregular than the Earth, but not hugely more irregular.)

Rare Earth?

[K. S. Kyosuke]

I believe I've read similar arguments some time ago in a book titled Rare Earth: Why Complex Life is Uncommon in the Universe. It was published a decade ago. So it's a slow news day again, I guess. ;-)

Re:Rare Earth?

[K. S. Kyosuke]

(Just to be a little bit more specific, this was about the "how important plate tectonics may be to life" part, not about new findings in the area of plate tectonics mechanisms which I'm sure are new.)

Re:Rare Earth?

[radtea]

You added your own addendum, but it's worth repeating: the idea that plate tectonics is important to life is not new.

The detailed model as to how and why plate tectonics got going on Earth and that also explains why it didn't get going on Venus is both new and interesting, which is pretty much the definition of "news for nerds, stuff that matters", eh?

Re:Rare Earth?

[K. S. Kyosuke]

It's the editing of the submission that I find (mis)leading.

Re:Rare Earth?

[Tablizer]

But we don't know if Earth's path to complex life is the only viable path. There may be "other angles" to get to complex life. We only have one sample to judge on.

Re:Rare Earth?

[RockDoctor]

the "how important plate tectonics may be to life"

To complicate matters (and yes, I read Ward & Brownlee's book when it came out too. It was an interesting read, but not 100% convincing. But then I am a geologist, not an OOL researcher.), when life started around 3800 million years ago (possibly as early as 4300 million years ago) the tectonic regime was decidedly different to today. This was probably driven by the higher heat flow of the early Earth, as there were more radioactive materials around then.

Modern plate tectonics seems to have started around 2500 million years ago. In the Archean, the tectonic style seemed to have much smaller microplates with narrower oceans and narrower subduction belts.

Why?

[StripedCow]

Without plate tectonics, carbon would build up in the atmosphere

Why is that?

Re:Why?

[Anonymous Coward]

How much limestone do you think is on earth?

Re:Why?

[K. S. Kyosuke]

If you bothered to read the article (or the book I linked), you'd find out that plate tectonics is crucial in the long-term carbon cycle that snatches carbon-containing minerals and, passing through subduction zones, deposits them in the depths of the Earth. (I'm not a geologist but I also vaguely recall that the hydration of these minerals contributes to the increased levels volcanic activity near the subduction zones, by means of lowering the melting point of rocks - which is how the cycle gets closed, since this volcanic activity releases the carbon back.)

Re:Why?

[Anonymous Coward]

Not a whole lot, really. It's a fucking huge planet.

Re:Why?

[Anonymous Coward]

Volcanos release carbon in the atmosphere. This carbon can be fixated in carbonate rocks or in organic carbon (mainly in carbonate rocks), but only up to a point. Plate tectonics provide a good way of putting carbon back in the mantle by subduction (sinking plates in the deep Earth).
 

Re:Why?

[tomhath]

which is how the cycle gets closed, since this volcanic activity releases the carbon back

That's kind of the question though. A huge amount of carbon is tied up in the Earth's crust. Some gets pulled down into the mantle, some gets released. From what I've read that cycle is in balance. So why wouldn't the carbon in the limestone stay there without tectonics?

Re:Why?

[K. S. Kyosuke]

I'm not sure it's about the limestone "not staying there", I always understood it as a matter of increasing the crust's overall absorbing capability, by circulating it over greater thickness of rock layers. If you absorb as much CO2 in a comparatively thin (but static) layer of rocks near the surface as you can (with the absorption speed steadily decreasing), what happens then to the rest of atmospheric CO2? That might just be the thing that happened to Venus. Or not. I'm not the expert, I'm afraid.

Re:Why?

[BitZtream]

So basically you're just making shit up as you go? Somehow you think that the crust wouldn't be layered without plate tectonics even though that isn't the reason the crust is layered in the first place ...

In that situation, when you can just make up silly answers to the holes in your theory, any theory can look sound.

Re:Why?

[K. S. Kyosuke]

If by "making shit up as I go", you mean "recalling interesting stuff from books I've read years ago", then yes. Otherwise you're not making too much sense.

Re:Why?

[Anonymous Coward]

So why wouldn't the carbon in the limestone stay there without tectonics?

Because no tectonics does not mean no volcanoes.

Re:Why?

[Anonymous Coward]

Angry internet nerd is angry internet tough guy nerd.

The geology department is trying to...

[Anonymous Coward]

The geology department is trying to justify themselves again - "Some scientists think that plate tectonics are essential for life". What a load of crap!

What a dumb article, the dirt monkeys make this supposition: "Venus doesn't have life because there are no tectonics (we think)". Maybe it doesn't have life because it's being scorched by a nuclear furnace????

Re:The geology department is trying to...

[oodaloop]

Maybe it doesn't have life because it's being scorched by a nuclear furnace????

Whew! Good thing Earth isn't being heated by a giant thermo-nuclear oven too!

Re:The geology department is trying to...

[Anonymous Coward]

"Heated" and "Scorched" are two different things... Thank you for playing, come again.

Re:The geology department is trying to...

[Tablizer]

but we are being "lightly toasted", not "scorched"; that's the difference. (Time to use cooking terms, for libraries-of-congress analogies are getting old.)

Re:The geology department is trying to...

[CrimsonAvenger]

Maybe it doesn't have life because it's being scorched by a nuclear furnace????

Whew! Good thing Earth isn't being heated by a giant thermo-nuclear oven too!

Venus gets about twice the solar irradiation we do here. If we got 2.5kw or so per square meter here, this planet would be uninhabitable too.

And since the Great Oxygen Event had a biological cause, it's probable we'd have a CO2 atmosphere too, with or without plate tectonics, if we had Venus levels of solar irradiation.

Re:The geology department is trying to...

[Eunuchswear]

Venus gets about twice the insolation that the Earth gets, not an amazingly large amount more.

Re:The geology department is trying to...

[Hognoxious]

"Some scientists think that plate tectonics are essential for life"

I think it are singular, but I might be wrong because I studied a physic and a small economic.

Re:The geology department is trying to...

[Anonymous Coward]

Insolation isn't the issue. Mercury gets around 3.5 times that of Venus, but is cooler.

Venus' temperature is largely due to an extreme case of the greenhouse effect, arising from a dense, CO2-rich atmosphere.

Re:The geology department is trying to...

[dryeo]

Venus is still in the Goldilocks zone, which is why it was expected that Venus would be covered with steaming jungles and inhabitable until we actually measured the temperature and it was such a surprise that it was so hot. This would have been even more true early in the Solar Systems history when the Sun itself was 25% cooler.
BTW, even the Earth would be an iceball at our distance from the Sun without the greenhouse effect which raises temperatures something like 40K

Re:The geology department is trying to...

[Anonymous Coward]

"BTW, even the Earth would be an iceball at our distance from the Sun without the greenhouse effect which raises temperatures something like 40K"

If this were true, why when you compare the temperatures on earth and venus at the same pressures, is the venus temp ~1.176x that of earth. This happens to be the temperature difference we would predict based on distance from the sun alone. I have read that venus' high temperature is caused by greenhouse effect, but also that the clouds reflect light thus preventing a greenhouse effect there. The theory does not seem to make sense or be able to explain the data I mention above.

Re:The geology department is trying to...

[Anonymous Coward]

If you want to ignore the effects of trapped heat, then just use the Stefan-Boltzmann law to find the equilibrium temperature of Earth. If you ignore Earth's albedo, you get a temperature just above freezing, and taking into account the albedo you get a temperature about -15 C, when the actual average surface temperature is about 15 C. The same could be done for Venus, It wouldn't be surprising that at the same pressure level you get the 1/sqrt(r_orbit) effect, since at the same pressure that means you have about the same amount of atmosphere above you in both cases. Although an amount of coincidence is involved because of the different compositions, and the comparison fails for comparing higher parts of the atmospheres since Venus lacks a stratosphere

Re:The geology department is trying to...

[Anonymous Coward]

I'm not clear on whether you are disagreeing with my point or not. The 1/sqrt(r-orbit) effect (perhaps we could call it "Huffman effect" since that is the name of the guy who appears to have first noted it) means either
1) An extremely unlikely coincidence has occurred, although I do not know how we could give a probability to this
2) Greenhouse effect does not exist
3) There is some kind of balancing mechanism that is driving the earth and venus atmospheres to the same/similar state. The primary difference between the two planets (with respect to determining temperature) seems to be input from the sun and the thickness of the atmosphere. The system then finds some combination of albedo, composition, etc that achieves a stable temperature/pressure for a given amount of incident energy.

Re:The geology department is trying to...

[Anonymous Coward]

Number 2 doesn't follow, as we can measure the albedo, incoming and outgoing energy, and see that some is being trapped. As to number one and three, you can see it doesn't work when comparing Mars to Earth's upper atmosphere, and it doesn't work comparing other parts of Earth's atmosphere to Venus. But there is some feedback considering that temperature affects how easily a planet's atmosphere is stripped off, among other factors like magnetic field.

Re:The geology department is trying to...

[Anonymous Coward]

First, the energy can be trapped without "greenhouse effect". Second, yes, the Huffman effect only works for earth troposphere pressures (and perhaps higher?). Also, #3 does not claim that there is only one stable state, only that some states are more stable than others and the earth/venus systems appear to have found the same solution.

Re:The geology department is trying to...

[RockDoctor]

The geology department is trying to justify themselves again

You typed this on a computer that you personally carved from a lump of tree. Oh, but you did the carving with a flint knife.

Sorry, but you've just done the geology department's self-justification task for them. You've left them with nothing to do!

this makes no sense to me.

[Noah Haders]

things that make no sense: 1) that CO2 would be poisonous? 2) venus has no atmosphere because it is so close to the sun 3) it has a molten surface because it is so close, so there is no "crust". 4) it is like that planet in star wars. the one with the molten surface.

Re:this makes no sense to me.

[Anonymous Coward]

It doesn't make sense to you that a 96% CO2 atmosphere is poisonous? Really? How about Mercury? Does it have a molten surface? Why are there so many idiots and morons these days?

Re:this makes no sense to me.

[Anonymous Coward]

Poisonous is not always a question of composition but can be a question of amount.
Oxygen is toxic to humans if you bring the concentrations up high enough.
Increase the O2 even more and you have Apollo 1 all over again.

Re:this makes no sense to me.

[bluefoxlucid]

I want to see a model of a Venus carbon scrub. 96% CO2? Earth is 20% O2, 0.035% CO2. Venus has 3.5% nitrogen. If we brought the CO2 down to Earth levels, the atmosphere would be 1% CO2, 99% nitrogen. Obviously, instead, you'd have a ton of oxygen--but if you could find hydrogen, you could make vast amounts of O2.

I went to research this and ... someone has already worked it out. Bombarding Venus with hydrogen would produce a 3 bar atmosphere, 80% coverage with water, 10% of the water on the earth's surface but Venus is flat. Habitable. Probably not for humans, but we could continuously dump life there and it would eventually adapt. Building an ecosphere would be hard; it would be easier to seed with microbial life and wait a billion years. Rapid terraformation is hard; we could use a temporal bubble to do it, otherwise not so great.

Re:this makes no sense to me.

[atherophage]

Plate tectonics is a theory (http://en.wikipedia.org/wiki/Plate_tectonics); one with a great many believers. Velikovsky writes Venus is hot because it is so young; having been a comet not that long ago, a theory too. An idea based upon another assumption, albeit one sold as fact, remains an idea.

Re:this makes no sense to me.

[BitZtream]

A basic biology class will tell you that CO2 is poisonous to a great many things ... like everything that breaths oxygen.

http://en.wikipedia.org/wiki/H...

The rest of your post could be solved if you opened any 3rd or 4th grade science book ... not sure what planet you're thinking of, but its not venus, which has both an atmosphere and a solid surface.

http://en.wikipedia.org/wiki/V...

It makes no sense because you have absolutely no idea what you're talking about.

Re:this makes no sense to me.

[Noah Haders]

there's a difference between something that's poisonous and something that suffocates you from lack of oxygen. for example, carbon monoxide is poisonous because it neutralizes your red blood cells, so you die even though the % is so low that it doesn't impact O2 %. So my question, is CO2 really poisonous or does it just cause suffocation?

Re:this makes no sense to me.

[Noah Haders]

heliocentrism is also a theory taken as fact, and notbody is even trying to disprove it any more. geocentrism ftw, it's the only one that makes any sense.

Re:this makes no sense to me.

[cant_get_a_good_nick]

Though I don't know the exact mechanism, I'd say to watch Apollo 13. Watch how much effort they put in to the CO2 scrubbers, to remove carbon dioxide from the air. They had sufficient oxygen, it was the CO2 levels that were too high. That's what was making them sick.

Re:this makes no sense to me.

[Anonymous Coward]

http://upload.wikimedia.org/wi...

Re:this makes no sense to me.

[Anonymous Coward]

As the partial pressure of CO2 increases, your blood has trouble getting rid of the CO2 in it. This happens long before the oxygen gets displaced, and you wouldn't be able to live in an environment that had the same amount of oxygen but much higher CO2. In effect, a lot of CO2 acts parallel to carbon monoxide, just it takes a lot more.

Re:this makes no sense to me.

[Noah Haders]

I don't need to watch Apollo 13 because I watched gravity. also Apollo 11 was the more successful one so why would I watch a movie about the less successful one???

Re:this makes no sense to me.

[Anonymous Coward]

The atmosphere is 78% nitrogen, and we breath it just fine. But air of 5 - 10% carbon dioxide is far more than enough to kill you. This happens because carbon dioxide is toxic to humans and nitrogen is not. It has nothing to do with oxygen deprivation.

As anyone who has taken college level biology will know, the hemoglobin found in red blood cells has two functions. The first is to transport oxygen from the lungs to the rest of the body, because oxygen is needed for cellular respiration (mainly the electron transport chain). The second function is to remove CO2 from the body cells and send them to the lungs. CO2 is the byproduct of cellular respiration, so if red blood cells did not transport it out, it would quickly accumulate in the body and make it too acidic to function (carbon dioxide plus water makes carbonic acid). This is why it is so critical for hemoglobin to be able to transport CO2 out of the body. The problem is that since hemoglobin can bind both CO2 and oxygen, high CO2 levels will begin to "crowd out" oxygen and hog up all of the hemoglobin, leading to suffocation. But even though the atmosphere is 78% nitrogen, this does not happen with nitrogen because nitrogen is not able to bind to hemoglobin at all. Evolutionarily, there is no reason for hemoglobin to have this ability.

tl;dr It's not about lack of oxygen. CO2 is toxic, nitrogen is not even though there is much more of it.

Re:this makes no sense to me.

[cant_get_a_good_nick]

1) that CO2 would be poisonous?

Water in sufficient quantities is toxic. I don't even mean in the drowning sense, or the silly DiHydrogen Monoxide jokes, but if you have too much water, it can kill you.

Nitrogen also works this way. Nitrogen in air, normal pressure, is fine. Nitrogen under pressure can kill you.

Too much oxygen can make you space out.

There are a lot of things that follow this - if you think of normal doses of heat, or electricity, you're fine. If too much, you die. It doesn't take a lot of thinking to come up with examples.

Re:this makes no sense to me.

[Anonymous Coward]

heliocentrism is also a theory taken as fact, and notbody is even trying to disprove it any more. geocentrism ftw, it's the only one that makes any sense.

We've known for almost 100 years that heliocentrism isn't accurate.

Re:this makes no sense to me.

[Anonymous Coward]

The problem is that since hemoglobin can bind both CO2 and oxygen, high CO2 levels will begin to "crowd out" oxygen and hog up all of the hemoglobin, leading to suffocation.

You lost me here. If CO2 and O2 both bind equally to hemoglobin, then what causes CO2 to be "released" in favor of O2 in the first place? (i.e. what causes the exchange during a given breath?)

Re:this makes no sense to me.

[Anonymous Coward]

Simple differences in concentration, combined with differences in binding strength between the two molecules.
When there is less 'free' CO2 than O2, more O2 will bind to the available receptors. (Especially as it binds preferentially.)
As CO2 levels rise, less and less O2 is available to 'find' and bind to the receptors on hemoglobin, resulting in less and less O2 being transported into the body.
CO, on the other hand binds *much* more strongly than O2, and as a result, it takes very high concentrations of O2, and/or long periods of time to flush CO from the bloodstream.

Re:this makes no sense to me.

[Anonymous Coward]

To add onto the other AC's helpful response, you can think about it as a sort of diffusion process. When blood reaches the lungs, it (and the hemoglobin within it) is rich in carbon dioxide while the lungs are rich in oxygen, so CO2 diffuses out of the blood and into lungs and oxygen flows from the lungs to the blood. When blood reaches body tissues, the body tissues have lots of CO2 and little oxygen compared to the blood, so the CO2 flows from the tissue to the blood and oxygen in the opposite direction. As the other AC already said, CO2 has a much higher binding affinity for hemoglobin than oxygen, which is why it can be a deadly poison even at low concentrations.

Fun fact: breathing is actually more driven by the need to exhale CO2 than the need to inhale oxygen. This is part of the reason that swimmers continue to exhale while they are holding their breath underwater.

Re:this makes no sense to me.

[Anonymous Coward]

Obvious troll is obvious. Go away, please.

Re:this makes no sense to me.

[dryeo]

Gravity is also a theory and yet hardly anybody argues about its existence.

Re:this makes no sense to me.

[OneAhead]

CO2 also reversibly "neutralizes your red blood cells"; the reason we're alive is that it only does so at a much higher concentration than CO. Once the CO2 level goes above about 10% for more than about 15 minutes, you'll likely suffer brain damage and/or death, no matter how much oxygen there is in the air.

Re:this makes no sense to me.

[Hognoxious]

The law of mass action, you oik.

Re:this makes no sense to me.

[cusco]

Velikovsky? How does his foolishness fit with your 'Electric Universe' foolishness?

Re:this makes no sense to me.

[dryeo]

Much as a broken clock is right twice a day, Velikovsky was the only one who predicted that Venus would be a furnace.

Re:this makes no sense to me.

[Anonymous Coward]

Or that Jupiter would have RF emissions.

Re:this makes no sense to me.

[cusco]

They had a fairly good idea that the surface temperature was well above the boiling point of water by 1940, so I'd hardly say "the only one."

Just found out that Velikovsky was a proponent of the Electric Universe quackery as well. I guess if you're going to be wrong you may as well be extravagantly wrong.

Re:this makes no sense to me.

[RockDoctor]

Because we allowed their parents to breed.

Re:this makes no sense to me.

[RockDoctor]

A basic biology class will tell you that CO2 is poisonous to a great many things ... like everything that breaths oxygen.

Probably the majority of life on Earth needs or can tolerate the presence of oxygen, if you measure it by tonnage of organisms. However if you measure by disparity (number of species and variety of metabolic processes) it's a much more balanced picture.

Re:this makes no sense to me.

[RockDoctor]

for example, carbon monoxide is poisonous because it neutralizes your red blood cells,

Wellll ... actually, what CO does (NB : CO not CO2) is bond onto haemoglobin within the red blood cells and NOT release. So that molecule of haemoglobin becomes effectively useless. Oxygen will cycle onto and off the haemoglobin every couple of minutes (circulation time from lung to capillary and back to lung). CO will take hours on average to be released by the haemoglobin.

so you die even though the % is so low that it doesn't impact O2 %

My diving text books when I was learning quoted that a cigarette with 0.5% CO would knock out between 5 and 10% of your haemoglobin. So don't smoke before a dive. (Yes, people have died to learn this lesson.)

So my question, is CO2 really poisonous or does it just cause suffocation?

CO2 does a number of things : it increases the blood's acidity, which messes up a lot of things including the ability of haemoglobin to pick up oxygen. AND it acts as an asphyxiant (suffocates you). Plus, it's rarely the only thing going on at the time. Most people who are exposed to excessive CO2 do so in the case of fire, when there's a lot going on. We use CO2 floods as a fire-fighting system at work, and the alarm systems are really serious about getting the fuck out of the area if the CO2 flood is going to be released.

Re:Carbon dioxide is *NOT* toxic. [Zepped!]

[Tablizer]

Are you a plant?

Yes, but call me Robert.

geos' theory half-baked

[Thud457]

ob. The Far Side reference

Wow. Talk about ignorance.

[mmell]

I mean here, not from the article's author.

If instead of yelling about how Mr. Bercovici's theory doesn't explain life, the Universe and everything we accept that he has provided a reasonable theory explaining one of the factors which led to the current difference between Earth and Venus, the conversation here might be more productive.

Yes, Venus gets considerably more energy from the Sun than Earth does. Yes, this alone could reasonably be expected to make it very different from Earth. Is that the only thing which caused Venus to be different from the Earth? If not, it might be interesting to know what other factors resulted in the differences we see - hence, the article exploring how plate tectonics may have contributed to the differences we see.

Oh, one last observation - Mr Bercovici has postulated a theory. I'm sure he started with a hypothesis for which he then sought supporting evidence, which he has provided. So far, sounds like good science to me.

Venus assumed to be 200 degrees hotter?

[erice]

From TFA:

the Venus model, which was a couple hundred Kelvin hotter,

So, how does it get so much hotter than Earth? It is certainly that much hotter now but that is attributed almost entirely to the greenhouse effect. However, the article earlier states:

Without plate tectonics, carbon would build up in the atmosphere. Venus, which does not have tectonics, shows the results: an atmosphere that is 96 percent carbon dioxide.

So, because plates did not form, Venus experienced a runaway greenhouse effect and high temperatures. But high temperatures are supposed to prevent plates from forming. A little circular, no?

Don't get me wrong: this is interesting work but it doesn't really answer the question of how Venus became the way it is . To close the gap, you need to assume that:
a) Venus started out 200K hotter though some other means (Proximity to the Sun is not generally considered sufficient for that)
-or-
b) Venus plate tectonics stalled early on for some other reason, allowing the greenhouse effect to take over.

Re:Venus assumed to be 200 degrees hotter?

[Anonymous Coward]

From the paper:

A similar exercise using hotter Venusian surface conditions permits
a comparison to Earth’s putative twin25–27.Using the same material properties
but a lithosphere temperature elevated by 200–400K above the
Earth-like case, the damage number D is reduced by a factor of about
10, and the healing numbers Ci and CI are increased by a factor of up to
10 (see Methods). In this case, as a downwelling migrates to various
positions (see Fig. 2), only very faint weak zones accumulate because
damage itself is weaker while healing is stronger, thereby resulting in
zones of passive divergence and strike-slip vorticity about an order of
magnitude weaker than the convergence rate. The final flowfield is dominated
by convergence, giving the appearance of a subduction-only surface.
This result provides a simple explanation for why Venus possibly
has subduction zones28, but no extant plate tectonics.

So they simply ran the simulation assuming higher temperature at the beginning. The paper does not appear to discuss CO2 at all. All of that greenhouse effect stuff seems to be an aside added by the journalist.

Without plate tectonics, carbon would build up in the atmosphere. Venus, which does not have tectonics, shows the results: an atmosphere that is 96 percent carbon dioxide. It's toxic. Yet Venus is about the same size and composition as our planet, so why doesn't it have plate tectonics?

I do not understand the purpose of this line about "It's toxic". It does not really have any meaning (toxic to what?) and is not related to the point of the article.

Re:Venus assumed to be 200 degrees hotter?

[Anonymous Coward]

May be was the other way:
- Venus started with a cooler core (a few thousands degrees cooler) (may be has not enough radioactive materials (uranium) in the core, so no further heating)
- Because there was not enough heat to maintain a liquid core, the entire planet began to radiate heat to space and to solidify
- Because of the solidification, the plate tectonics stalled

Compute Hours?

[nobdoor]

"The model uses physics at the one-millimeter rock grain scale to explain how the whole planet behaves."

A 3,000 x 3,000 x 3,000 grid is considered very large for modern scientific models. Assuming they are working on a cartesian grid, and an earth diameter of 12,000 km, their model would be 12,000,000 x 12,000,000 x 12,000,000; twelve orders of magnitude larger than the biggest physical model I've ever heard of.

This cannot be the case.

Re:Compute Hours?

[crunchygranola]

"The model uses physics at the one-millimeter rock grain scale to explain how the whole planet behaves."

A 3,000 x 3,000 x 3,000 grid is considered very large for modern scientific models. Assuming they are working on a cartesian grid, and an earth diameter of 12,000 km, their model would be 12,000,000 x 12,000,000 x 12,000,000; twelve orders of magnitude larger than the biggest physical model I've ever heard of.

This cannot be the case.

Whew! Its a good thing they never claimed they were doing any such thing.

"physics at the one-millimeter rock grain scale" does not mean that they were using a model grid of that same scale.

To show that the assumption that it must, or even should, is incorrect consider any engineering model that involves the effects of static friction.

The phenomena that cause static friction exist on the molecular and atomic level, and theoretical predictions of friction under arbitrary conditions need to be analyzed and calculated at that scale.

But once you have determined what the coefficient is under a given set of conditions, you only need to use the single number in a macro scale model.

That is what they did here. If you read TFA you will see that their macro model used coefficients calculated using the detailed physics.

Re:Compute Hours?

[cusco]

Thanks, that makes more sense. I also was wondering how the hell they managed to crunch the numbers for a grid that size, which from TFS sounds like what they were doing.

I wonder what assumptions they are making?

[grantspassalan]

Since nobody was around billions of years ago, many assumptions have to be made about conditions on earth at that time. This is true even more so about Venus. About the only thing these “scientists” can say for sure is that the mathematics and programming of their computer models are likely correct. That is certainly not true about the original assumptions used as a starting point. As the saying goes: “garbage in, garbage out”.

Re:I wonder what assumptions they are making?

[RockDoctor]

Since nobody was around billions of years ago, many assumptions have to be made about conditions on earth at that time.

So you look at proxies. For example, you might ask how we know that there was liquid water on the Earth's surface 3.5 billion years ago, as there were no people to witness it. But there WERE rocks to witness it. In particular, there were pebbles and sand grains that were being transported by the water, and their shape and grain size distributions match the shapes of modern water-transported sediments, so we deduce the presence of water.

These assumptions are cross-correlated. They link together to produce self-consistent models.

Simulation != Reality

[Anonymous Coward]

"According to David Bercovici, a geophysicist at Yale who was an author on the paper, the model also shows how plate tectonics emerged on Earth but not on her twin."

I doubt the actual researcher said this. The model shows how plate tectonics could have emerged.

Re:Wow. Talk about ignorance.

[Anonymous Coward]

I think most people here are taking issue with the journalist and not the researcher. She should read more Feynman if she really believes the tautological narrative presented in paragraph 3 and that simulation=reality as implied by the headline.

Good question.

[mmell]

I'd always thought it might have something to do with lower planetary mass and surface gravity. Works for Mars, but Venus is also smaller than Earth - and close enough to the Sun that solar wind should be stripping the atmosphere off into space.

IANARS.

Re:Good question.

[Anonymous Coward]

I searched around a bit. The answers seem to go something like this:

Venus has a strong ionosphere that protects it against violent solar winds. So, even though Venus has no intrisic magnetic field, it has an effective, induced magnetic field due to the interaction between the solar winds and the atmosphere, that protects it against solar winds.

Venus atmosphere is thick enough to have a consequent ionosphere, that would be the difference between Mars and Venus (and Venus was able to keep a thicker atmosphere due to its greater mass, contrary to Mars).

https://astronomy.stackexchange.com/questions/639/why-has-venuss-atmosphere-not-been-stripped-away-by-solar-wind

The chain of causality of this argument is fuzzy to me. "Venus has an induced magnetic field because of its thick atmosphere, the thick atmosphere is possible due to the induced magnetic field". It is like the chicken/egg problem.

The primary argument seems to be that venus' higher mass allowed it to retain a denser atmosphere originally, but this is always presented as an aside rather than the root cause for some reason.

Re:Good question.

[Anonymous Coward]

Same AC. Actually that argument still doesn't really explain anything because Earth is larger than Venus, has both types of magnetic fields, but has a much thinner atmosphere.

Re:Good question.

[mmell]

I'm guessing "IDGI" is not a good answer. :)

Re:Good question.

[Anonymous Coward]

The controversy stems from recent observations that show Mars and Venus are losing oxygen ions from their atmospheres into space at about the same rate as Earth. This came as something of a surprise, since only Earth has a strong dipolar magnetic field that can prevent solar wind particles from slamming into the upper atmosphere and directly stripping away ions.

My opinion is that the magnetic shield hypothesis is unproven," said Robert Strangeway from UCLA. "There's nothing in the contemporary data to warrant invoking magnetic fields."

http://www.space.com/11187-earth-magnetic-field-solar-wind.html

So apparently no one knows why venus is so hot.

Re:Good question.

[Anonymous Coward]

Probably because the same reason it's spinning so slowly: the colission with a planetoid big enough to make a planet the size of Venus stop spinning must have been MASSIVE. And it surely released a lot of heat, too.

Just Right

[Baron von Daren]

Just another example on how many factors affect a planet’s ability to support life not to mention sentient species and civilizations. The more we learn, the longer the list becomes (e.g. the right kind of star system with the right kind of star, the right planetary materials in the right zone, the right kind of magnetosphere, the right kind of moon, shepherd planets, the right kind of galaxy/cluster, the right place in place in the galaxy/cluster, the right kind of geological tectonics, the right kind of asteroid/comet hits, the right kind of mass extinctions and evolutionary histories, and so on).

The universe (not to mention a potential multiverse) certainly contains many planets capable of supporting civilizations, but the numbers are certainly bleaker than the old Drake equations.

Re:Just Right

[cusco]

The Drake Equation didn't come with any numbers pre-decided. Some of the numbers, such as rate of star formation, were known. Some, such as percentage of stars with planets and percentage of planets in the 'Goldilocks Zone', are only becoming known now. Others, such as the percentage of planets that give rise to life, are still unknown. You can plug any numbers you want into any of the variables.

Re:Just Right

[Baron von Daren]

Indeed, but I wasn't commenting on the equation as much as the tendency to plug in optimistic numbers yielding estimates of tens of thousands of advanced civilizations in the Milky Way alone. I don't have the numbers handy (so my memory may be betraying me), but I believe that somewhere around 90% of stars, in our galaxy, reside in areas too violent to support life for the requisite periods of time regardless of all other factors. I'm not qualified in the least to say whether you facter that into R itself, or if fi is more appropriate. Either way, when you start trying to determine a sound value for ne considering myriad variables like magnetosphere, tectonics, temperature, sufficient H2O, etc., I'd guess N is orders of magnitude less than what was in vogue decades ago.

Re:Just Right

[RockDoctor]

the right kind of moon

That's a very popular claim - that the presence of a large Moon was necessary to the origin of life/ complex life/ civilisation - but I've only heard it made by popular science journalists. I've not heard a serious scientist make that assertion and then defend it.

It may be true, but I wouldn't make that claim, because I wouldn't like to try to defend it.

Re:Just Right

[Baron von Daren]

Fair enough; of course I would be hard pressed to defend any of this in a rigorous manner as I am neither a trained scientist nor in the habit of reading scholarly papers, journals, etc. The 'scientific' facets of my worldview are largely informed via popular scientific outlets, some more rigorous than others. I certainly haven't scoured the scientific papers on the subject.

On the other hand, I wonder what you mean by 'very popular claim?' Do you mean a claim made often by non-scientist? Perhaps, but there are easily accessible statements by scientist from various disciplines that speak to the Moon's theorized role in Earth's evolutionary process from the stabilization of the axis, to the early tilde affects on Earth's magma (when the Moon was much closer), to decreasing the amount of asteroid and comet hits we take, to regulating ocean tides, etc. Again, these come to me filtered through popularized media, but they are claims made by scientists.

In any case, I wouldn't argue that a moon like the Moon is necessary for life, nor could I, but don't think its unreasonable to argue that it makes Earth a much more hospitable place to live. And again, the Drake equation isn't about just any kind of life, but about sentient life capable of reaching advancement roughly on par with human culture (or beyond of course). Is a Moon like moon a necessary condition for advanced sentient species? Probably not, but there is probably a critical mass of non-necessary conditions that is necessary...if that makes any sense.

Re:Just Right

[RockDoctor]

On the other hand, I wonder what you mean by 'very popular claim?' Do you mean a claim made often by non-scientist?

It's something that I hear a lot on things like Discovery channel. I do spend quite a lot of time and effort trying to keep up with the literature, and I don't see such claims being made or repeated there.

Moon's theorized role in Earth's evolutionary process

1. from the stabilization of the axis,
2. to the early tilde affects on Earth's magma (when the Moon was much closer)
3. decreasing the amount of asteroid and comet hits we take,
4. to regulating ocean tides, etc

From the top ... stabilisation of the Earth's axis? Yes, the Moon does stabilise the Earth's axis, but how important is that. Mars does suffer considerable excursions of it's axial tilt, but even so it only moves at around a degree per megayear. The rate of movement of climate zones resulting from global warming is much faster than that. Yes it's an efect, but is it fundamentally an important one? We need more examples (i.e. planets with life) to address that question.

early tide effects? Shrug. When the Earth was a magma ocean, it was probably a bit early for the development of life. By a couple of hundred million years later, there was a solid crust with liquid water cycling on it (the oxygen isotope data from the Jack Hills zircons tell us that). So ... the magma ocean phase wasn't significant. And I'm still not sure how "tidal effects" would have changed the origin and development of life.

decreased asteroid and comet hits? Meh. The decrease would be very small, if anything. The Moon covers only a tiny fraction of the sky. It might actually increase the number of hits. However some work about 4 or 5 years ago showed that for most impacts - up to a 100km or so impactor, which are rare - the deep basins of the oceans don't get boiled dry, so again, it's really a "Meh" in terms of it's effects on OOL.

regulating ocean tides? Again, Meh ; the intensity and frequency of tides have changed, greatly, since the origin of life (we don't know exactly how much ; the coupling between Earth's rotation and the Moon's orbit is quite sensitively dependent on the amount of shallow seas and the orientation of coastlines, to change the position of the oceanic tidal bulge with respect to the Earth-centre to Moon-centre line. That affects the torque that the Earth applies to the Moon and vice versa. We don't have enough information (because plate tectonics is destructive of information about previous continental arrangements) calculate the exact trajectory of orbital parameters and Earth's rotation. We aren't even really sure if the Moon originally formed at the Roche limit, or significantly outside it. Or even if the Moon formed in one go, or by the merger of several moonlets in the few decades following the Giant Impact. Indeed, while the "Giant Impact" is by far the consensus for the origin of the Moon, it is turning out to be hard to get it to work exactly correctly.

Given all of these issues, I wouldn't attempt to defend the proposition that "a large moon is necessary for the origin of life". It may be a true proposition, but I don't think that the state of knowledge at the moment allows one to claim it as a fact.

Over to you.

Re:Just Right

[Baron von Daren]

You said:

Given all of these issues, I wouldn't attempt to defend the proposition that "a large moon is necessary for the origin of life". It may be a true proposition, but I don't think that the state of knowledge at the moment allows one to claim it as a fact.

Over to you.

Consider these statements from my last reply:

...I wouldn't argue that a moon like the Moon is necessary for life, nor could I...

and

Is a Moon like moon a necessary condition for advanced sentient species? Probably not...

As such, I'm not sure we disagree significantly on that specific point.

My point is that I once held an fairly optimistic stance regarding the possible numbers of alien civilizations 'out there.' That stance has been tempered and refined as we discover just how many things Earth has going for it. Are all of them strictly necessary? By no means, but there is probably a critical mass in the matrix of variables needed to foster not only life, but an ongoing evolutionary process. Will there be harsh world outliers? Probably so given the number of potential planets out there, but I am simply saying that the known universe is far more inhospitable than I had once imagined.

Just as an aside; I can’t tell you the last time I watched the Discovery channel or its ilk. I do watch Nova and Nature on occasion, and I really enjoyed Brian Cox’s Wonders of the Solar System and Wonders of the Universe (which may actually show on Discovery for all I know). I see other things from time to time, but I find most TV shows repetitive and over-simplified, so I stopped watching them, by and large, many years ago.

Re:Carbon dioxide is *NOT* toxic. [Zepped!]

[Eunuchswear]

Bob is that you?

Why are you so angry?