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lpetrich
2001-Nov-17, 02:02 PM
Some questions about:

http://www.astronomy.com/photogallery/gallery_large.asp?idObjectLibraryGUID={D99E68AC-5A09-11D5-9190-000629551DBC}

There is no supporting discussion or any links to such discussion /phpBB/images/smiles/icon_frown.gif

However, that diagram displays the results of some recent work on the near future of the Earth and when it will become uninhabitable for most complex life.

Basically, the Earth becomes too hot in a range of 60 - 1300 myr, the Earth runs out of CO2 from 350 to 1300 myr, and it runs out of water from 350 to 1200 myr. I wonder if these are reasonable figures; the proposed mechanisms are entirely reasonable ones.

The CO2 mechanism is a sort of geochemical thermostat; CO2 is released by volcanoes and is mainly fixed by weathering.

CO2 is a greenhouse gas; it helps the Earth's atmosphere retain heat. But this retained heat speeds up weathering fixation until the fixation rate is equal to he release rate. This mechanism is a proposed resolution of the "faint early Sun" paradox; in the past, the Earth's atmosphere had continued much more CO2, which kept it at near-present temperatures despite there being less sunlight.

However, as the Sun brightens, the CO2 level has gone down, and the present level is almost dangerously low. If it becomes much lower, then it could interfere with plant photosynthetic productivity, since much light energy may have to be assigned to the task of collecting CO2.

And as the Earth heats from the brightening Sun, the stratosphere will also heat enough to allow water vapor to travel up to the ozone layer, where it will be dissociated into hydrogen and oxygen. The hydrogen will escape, draining the Earth's water supply and making the entire Earth a bone-dry desert.

As to heat as a limitation for life, there is indirect evidence from the biotas of hot springs; at higher temperatures, their biotas become more and more simplified, with whole ecological niches, such as for "grazers", unpopulated. Could it be that it is too difficult for the more complex organisms to evolve adaptation to high temperatures because of excessive interdepedence in their biochemistry?


Fish 38 C (122 F)
Arthropods (insects, ostracods): 45-50 C (113-122 F)
Vascular Plants: 45 C (113 F)
Mosses: 50 C (122 F)
Protozoa: 56 C (133 F)
Algae (eukaryotic): 55-60 C (131-140 F)
Fungi: 60-62 C (140-144 F)
Photosynthetic bacteria: 70-73 C (158-163 C)
Organic-eating bacteria: 90 C (194 F)
Methanogens: 110 C (230 F)
Sulfur-dependent archaea: 115 C (239 F)


Note: photosynthetic bacteria include cyanobacteria, with their plantlike oxygen-releasing photosynthesis.

URL: http://www.bact.wisc.edu/Bact303/b10

Finally, there is a distinction between "Red Giant" and "Red Giant II". Could that be a division between hydrogen shell burning and helium core burning?

Note: myr = million years

Kaptain K
2001-Nov-17, 03:02 PM
Let's see now. The Earth "may" become too hot for habitation as soon as 60 million years from now. 60 million years ago, the dinosaurs had been extinct for 5 million years. I absolutely refuse to worry about something that far in the future.

David Simmons
2001-Nov-17, 03:39 PM
Isaac Asimov speculated that the greatest and most immediate threat is the depletion of phosphorous. I think that element is essential for vegetation and animals are all parasitic on vegetation, directly or indirectly.

Asimov's contention (I've forgotten what the title of the essay is, maybe someone will know) was that all of the phosphorus is gradually being washed into the oceans and not recovered. When it is depleted, vegetation will die and so will everything else on land.

That, of course, wouldn't be the end of the world, only the end of present land life. But even if it is - as one individual remarked concerning the atomic destruction of the earth. "After all, it isn't as if it were a major planet."

Of course, I don't think Asimov, or anyone else at the time, was aware of the life forms in the vicinity of the hot, deep sea vents.



<font size=-1>[ This Message was edited by: David Simmons on 2001-11-17 10:41 ]</font>

Hat Monster
2001-Nov-17, 08:39 PM
Kaptain K: The dinosaurs did not become extinct 55Ma ago. 65Ma, not 55Ma.

Kaptain K
2001-Nov-17, 09:11 PM
Kaptain K: The dinosaurs did not become extinct 55Ma ago. 65Ma, not 55Ma.
/phpBB/images/smiles/icon_confused.gif
Me thinks you need another cup of coffee or three. /phpBB/images/smiles/icon_smile.gif
I stand by what I wrote. /phpBB/images/smiles/icon_rolleyes.gif

ToSeek
2001-Nov-17, 10:16 PM
On 2001-11-17 15:39, Hat Monster wrote:
Kaptain K: The dinosaurs did not become extinct 55Ma ago. 65Ma, not 55Ma.



This reminds me of a joke that I hope the BA will permit.

It seems a touring lecturer on dinosaurs - let's call him Dr. Smith - came to the local library to give a talk. He was pleased to see that there was a good audience, and he began his talk, as he usually did.

"Sixty-five million years ago, the dinosaurs became extinct-"

He was somewhat nonplussed to see a hand go up at that point, but he had agreed to take questions at any time, so he called on the woman with her hand up.

She stood up. "Excuse me, Dr. Smith, but you were here five years ago and said exactly the same thing. Shouldn't it be 65 million and five years now?"

David Simmons
2001-Nov-18, 05:39 AM
On 2001-11-17 15:39, Hat Monster wrote:

Kaptain K: The dinosaurs did not become extinct 55Ma ago. 65Ma, not 55Ma.
/phpBB/images/smiles/icon_confused.gif

On 2001-11-17 16:11, Kaptain K wrote:

Me thinks you need another cup of coffee or three. /phpBB/images/smiles/icon_smile.gif
I stand by what I wrote. /phpBB/images/smiles/icon_rolleyes.gif




The Britannica gives the final extinction of dinosaurs as the end of the Cretaceous - 66.4 million years ago.

<font size=-1>[ This Message was edited by: David Simmons on 2001-11-18 00:41 ]</font>

Donnie B.
2001-Nov-18, 11:55 AM
On 2001-11-18 00:39, David Simmons wrote:


On 2001-11-17 15:39, Hat Monster wrote:

Kaptain K: The dinosaurs did not become extinct 55Ma ago. 65Ma, not 55Ma.
/phpBB/images/smiles/icon_confused.gif

On 2001-11-17 16:11, Kaptain K wrote:

Me thinks you need another cup of coffee or three. /phpBB/images/smiles/icon_smile.gif
I stand by what I wrote. /phpBB/images/smiles/icon_rolleyes.gif



The Britannica gives the final extinction of dinosaurs as the end of the Cretaceous - 66.4 million years ago.




... and five years... /phpBB/images/smiles/icon_biggrin.gif

Kaptain K
2001-Nov-18, 12:04 PM
OK! 60 MYA, the dinosaurs had been extinct 6.4 MY + 5 yrs. Is everybody happy now?

David Simmons
2001-Nov-18, 04:08 PM
On 2001-11-18 07:04, Kaptain K wrote:
Is everybody happy now?



Gee, it sure doesn't sound like it.

ljbrs
2001-Nov-24, 12:43 AM
Ipetrich:

As you suggested, the distinction between types of Red Giant stars has to do with the difference between (1) the evolution of stars which end up with lower-than 1.44 Solar masses (after shedding their envelopes from their red-giant days to become planetary nebulae and finally ending up as white dwarf stars); and (2) the evolution of much larger and much more massive Red Giant stars (which undergo the "onion-like" development), leading to Type II Supernovae and ending up as either Neutron stars or as Black Holes. A much clearer and more complete discussion of these distinctions is made in (my favorite) quick-reference books *Facts on File Dictionary of Astronomy* ([probably First], Second, Third, and Fourth Editions). It is also discussed in much greater detail in many books on Astrophysics.

ljbrs /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_biggrin.gif

Chip
2001-Nov-27, 04:59 AM
On 2001-11-17 09:02, lpetrich wrote:
Some questions about:

http://www.astronomy.com/photogallery/gallery_large.asp?idObjectLibraryGUID={D99E68AC-5A09-11D5-9190-000629551DBC}

[The]..."diagram displays the results of some recent work on the near future of the Earth and when it will become uninhabitable for most complex life."


Interesting. Judging from this article, and from what some other posters have written...and...being such an impossible optimist... I would say that if true, this prediction prompts us to continue to develop:

1. Advanced tech allowing us to colonize other worlds (first Mars) then gradually spreading beyond the solar system. (Over maybe 10 million years.) (Of course we'd physically evolve into something different along the way.*)

2. In the meantime, develop plants that don't need phosphorous. (-;

Then when things ran out, or the sun went "red giant" we (i.e. our descendants) would be strewn across a vast distance - but not the whole galaxy. (Not yet.) Ambitious eh?

* (Would we still appreciate Bach?)

Chip /phpBB/images/smiles/icon_wink.gif

David Simmons
2001-Nov-28, 02:55 PM
Here is a link that identifies a likely "end of the earth" routine. "Planetary Nebula" (http://news.bbc.co.uk/hi/english/sci/tech/newsid_1679000/1679435.stm)

NottyImp
2001-Nov-29, 09:18 AM
Given that we can hardly predict weather accurately further than 24 hours ahead, I'd be dubious at best about predictions that deal in millions of years. Even un-coupling the multiple effects that lead to present-day global warming is proving a difficult task for environmental scientists. And the ranges given are so large as to be almost meaningless.

Now, where's my pinch of salt...

_________________
Up the Imps!

<font size=-1>[ This Message was edited by: NottyImp on 2001-11-29 04:21 ]</font>

aurorae
2001-Nov-29, 04:19 PM
On 2001-11-17 10:39, David Simmons wrote:
Isaac Asimov speculated that the greatest and most immediate threat is the depletion of phosphorous. I think that element is essential for vegetation and animals are all parasitic on vegetation, directly or indirectly.

Asimov's contention (I've forgotten what the title of the essay is, maybe someone will know) was that all of the phosphorus is gradually being washed into the oceans and not recovered. When it is depleted, vegetation will die and so will everything else on land.

That, of course, wouldn't be the end of the world, only the end of present land life. But even if it is - as one individual remarked concerning the atomic destruction of the earth. "After all, it isn't as if it were a major planet."

Of course, I don't think Asimov, or anyone else at the time, was aware of the life forms in the vicinity of the hot, deep sea vents.



I'm sure he wasn't. It was only in recent years that chemosynthetic life was discovered.

I also wonder if he wrote the aove before the concept of continental drift was generally accepted?

Ocean floor material gets subducted beneath the continental plates. There aren't any truly ancient sea floors.

The ocean material can reach the surface through volcanoes. Including places where plates are spreading, like the mid-Atlantic ridge.

lpetrich
2001-Nov-30, 09:04 PM
NottyImp:
Given that we can hardly predict weather accurately further than 24 hours ahead, I'd be dubious at best about predictions that deal in millions of years. ...

LP:
What is difficult to predict is the day-to-day details; however, predicting overall climate has been much more successful.

Chip:
In the meantime, develop plants that don't need phosphorous. ...

LP:
However, phosphorus appears in several critical biochemical locations, notably in the nucleic acids (DNA and RNA). It also appears in the energy intermediate ATP (the RNA nucleoside adenosine with 3 phosphates whose phosphate-phosphate bonds contain the energy), some coenzymes, and some membrane lipids.

aurorae:
It was only in recent years that chemosynthetic life was discovered.

LP:
That is not quite correct. Chemosynthetic bacteria have been studied for decades. However, what aurorae may be referring to is the sort of ecology present around certain ocean-floor hot springs. These springs have sulfur compounds which some bacteria use for energy; these bacteria are then eaten by some of the other hot-spring inhabitants, which in turn may be eaten by others.

However, these hot springs are not completely independent of photosynthesis; in particular, they depend on reactions like

H2S + 2*O2 -> H2SO4

which depends on photosynthesis-produced oxygen.

Espritch
2001-Dec-01, 02:04 PM
It appears from the article that what we need to do (by "we" I mean our distant descendants) is construct some kind of orbiting sun screens to deflect some of the excess heat from the sun. That ought to keep the planet habital for a billion or so years longer. Once the sun goes red giant we might need to move the earth out to a more distant orbit using close passes by a big asteroid to gradually perturb it's orbit. Assuming that we can find a way to shield it from the effects of the sun going nova (bigger sun screens maybe?), we can then use the same method to move the orbit closer as the sun shrinks down to white dwarf status. Since white dwarfs cool very slowly, this should provide habitability for several billion years more. Phosphates and water can be replenished by mining comets and maybe Mars (I assume there are phosphates on Mars). So it's really just an engineering problem. /phpBB/images/smiles/icon_smile.gif


<font size=-1>[ This Message was edited by: Espritch on 2001-12-01 11:25 ]</font>

David Simmons
2001-Dec-01, 04:58 PM
On 2001-11-29 11:19, aurorae wrote:
Ocean floor material gets subducted beneath the continental plates. There aren't any truly ancient sea floors.

The ocean material can reach the surface through volcanoes. Including places where plates are spreading, like the mid-Atlantic ridge.


I think the point is that the rate of recycling is far, far too slow, given the need for phosphate fertilizers to support such a huge population on the earth.

Azpod
2001-Dec-01, 07:04 PM
On 2001-12-01 09:04, Espritch wrote:
It appears from the article that what we need to do (by "we" I mean our distant descendants) is construct some kind of orbiting sun screens to deflect some of the excess heat from the sun. That ought to keep the planet habital for a billion or so years longer. Once the sun goes red giant we might need to move the earth out to a more distant orbit using close passes by a big asteroid to gradually perturb it's orbit. Assuming that we can find a way to shield it from the effects of the sun going nova (bigger sun screens maybe?), we can then use the same method to move the orbit closer as the sun shrinks down to white dwarf status. Since white dwarfs cool very slowly, this should provide habitability for several billion years more. Phosphates and water can be replenished by mining comets and maybe Mars (I assume there are phosphates on Mars). So it's really just an engineering problem. /phpBB/images/smiles/icon_smile.gif


Build bigger sunscreens to protect the Earth (and other terraformed worlds, such as Mars and possibly Luna, Europa and Callisto as well) from the Sun going nova?! Man, at that point I think it'd be better to just leave! Surely we would have colonized worlds in other nearby star systems by then...!

After the Sun's done with the planetary nebula phase, we could always come back and re-colonize whatever worlds there are left. Assuming the Earth isn't consumed by the red giant phase, we could probably even come back to Earth to live-- for sentimental reasons and all that.

As for me, I hope my descendants get over the whole "mother world" thing and will be kicking it on a world somewhere orbiting in the life zone of a red dwarf that won't go nova for another 50 billion years. Heck, I hope they finally find a cure for death so I can be getting a tan on the beach right along with them! /phpBB/images/smiles/icon_smile.gif

Hey, what's the point of dreaming if you don't dream big?

Kaptain K
2001-Dec-01, 08:18 PM
FWIW - The Sun won't go nova, it is too small. For a Sol sized star, the sequence is: main sequence => red giant => white dwarf + planetary nebula => gradually cooling to black dwarf.

Azpod
2001-Dec-01, 09:45 PM
On 2001-12-01 15:18, Kaptain K wrote:
FWIW - The Sun won't go nova, it is too small. For a Sol sized star, the sequence is: main sequence => red giant => white dwarf + planetary nebula => gradually cooling to black dwarf.


Really...? I thought the cause of the planetary nebula was the star going nova and blowing everything but its core into space. If the Sun won't go nova, what causes the planetary nebula?

_________________
Just my two neurons worth,
Azpod... Formerly known as James Justin

[Edit: Cant spel]

<font size=-1>[ This Message was edited by: Azpod on 2001-12-01 16:45 ]</font>

David Simmons
2001-Dec-01, 11:05 PM
On 2001-12-01 16:45, Azpod wrote:

Really...? I thought the cause of the planetary nebula was the star going nova and blowing everything but its core into space. If the Sun won't go nova, what causes the planetary nebula?


I got a primer on them from Britannica. Here is a link to a recent discovery of one. Planetary Nebula (http://news.bbc.co.uk/hi/english/sci/tech/newsid_1679000/1679435.stm)

Kaptain K
2001-Dec-02, 12:34 AM
Azpod:
Really...? I thought the cause of the planetary nebula was the star going nova and blowing everything but its core into space. If the Sun won't go nova, what causes the planetary nebula?
The planetary nebula is formed by the high volume stellar wind of the red giant stage of the stars life. It is illuminated by radiation from the central stellar remnant. For a Sol type star, the PN is lit by flouressence from ultraviolet light from the white dwarf. The Ring nebula in Lyra is a good example. For a PN from a supernova the illuminating radiation is X-rays from the central neutron star. The Crab nebula in Taurus is a good example of this type.

Azpod
2001-Dec-04, 03:35 AM
On 2001-12-01 19:34, Kaptain K wrote:
The planetary nebula is formed by the high volume stellar wind of the red giant stage of the stars life. It is illuminated by radiation from the central stellar remnant. For a Sol type star, the PN is lit by flouressence from ultraviolet light from the white dwarf. The Ring nebula in Lyra is a good example. For a PN from a supernova the illuminating radiation is X-rays from the central neutron star. The Crab nebula in Taurus is a good example of this type.

So the Sun, when entering the PN stage, will shed most of its mass through intense solar wind...? Wow; so any planets capable of supporting life would likely be rendered uninhabitable because the atmospheres would be poisoned by the stellar material being shed.

Would a gas giant such as Jupiter be able to gain enough mass to ignite into a red dwarf by capturing enough of the nebula...?