# The End of the Earth.



## Scifi fan (Dec 9, 2008)

OK, this is a spin off from a thread I started, when we began talking of how the Earth would end. The first and most obvious is, BANG, when alien invaders blow up the planet. The second and, possibly, just as obvious is if the sun turns into a red giant and incinerates the Earth. Of course, it is very possible that, if the sun does expand, it could push the Earth away. 

We know very little of the solar system now, and our astronomers are scratching their heads as to why there seems to be some force that seems to either pull our spacecraft towards some destination or slow their travels. So far, there's not even theory to describe it. So, to get back to the topic, regarding the end of the Earth, anything goes. Just keep the discussion civil.


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## jojajihisc (Dec 9, 2008)

If you are talking about the actual disintegration of the planet itself then I would say our Sun is going to be the most likely candidate to do it. I'm not sure the Earth would be pushed away when the Sun begins to expand. I suppose it depends on which is going to be the stronger force - the repelling force of radiation pressure or the attraction of gravity from a less massive but much more voluminous star.

If you are talking about how humanity comes to an end on this planet then I would say nuclear holocaust. This has been the biggest threat since they were invented and will continue to be so for a long time.


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## Lillyanna (Dec 9, 2008)

Scifi fan said:


> Of course, it is very possible that, if the sun does expand, it could push the Earth away.


 
Do you mean that as the sun loses mass, the Earth might have a larger orbit?  I'm not sure if the orbit equation can be used this way (maybe just as a thought experiment?), but I could imagine that the distance between the sun and Earth would increase late in the star's life.

I'm not so sure about the "push"-ing part, though.

Where did you hear about this?


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## Zubi-Ondo (Dec 9, 2008)

This is the scoop from Wiki: The Sun is expected to become a red giant approximately 5 billion years from now. It is calculated that the Sun will become sufficiently large to engulf the current orbits of the solar system's inner planets, up to Earth, and its radius will expand to a minimum of 200 times its current value. The Sun will lose a significant fraction of its mass in the process of becoming a red giant, and there is a chance that Mars and all the outer planets will escape as their resulting orbits will widen. Mercury and most likely Venus will have been swallowed by sun's outer layer at this time. Earth's fate is less clear. Earth could technically achieve a widening of its orbit and could potentially maintain a sufficiently high angular velocity to keep it from becoming engulfed. In order to do so, its orbit needs to increase to between 1.3 AU (190,000,000 km) and 1.7 AU (250,000,000 km). However the results of studies announced in 2008 show that due to tidal interaction between sun and Earth, Earth would actually fall back into a lower orbit, and get engulfed and incorporated inside the sun before the sun reaches its largest size, despite the sun losing about 38% of its mass.  Before this happens, Earth's biosphere will have long been destroyed by the Sun's steady increase in brightness as its hydrogen supply dwindles and its core contracts, even before the transition to a Red Giant. After just over 1 billion years, the extra solar energy input will cause Earth's oceans to evaporate and the hydrogen from the water to be lost permanently to space, with total loss of water by 3 billion years. Earth's atmosphere and lithosphere will become like that of Venus. Over another billion years, most of the atmosphere will get lost in space as well; ultimately leaving Earth as a desiccated, dead planet with a surface of molten rock.

 - Z


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## Drachir (Dec 9, 2008)

I have a bit of a problem with the "pushing away" idea as well.  Anything that can push away the Earth almost certainly won't leave anything alive on it.


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## Scifi fan (Dec 9, 2008)

Well, there seems to be two sub threads - the first is how life on Earth would end, and the second is how the Earth would end.

I've never heard of the pushing away the Earth theory until now, but I know very little about astronomy. My gut instinct is that, left to nature, the planet would be engulfed by fire when the sun becomes a red giant. 

That said, I'm not convinced humanity wouldn't intervene. In a billion years, we may have enough technological know how to push the Earth into a further orbit or even drive it out of the solar system altogether. Remember what the puppeteers did with their five planets?


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## TheEndIsNigh (Dec 9, 2008)

Course we could just fire up the Hadron collider again and have ourselves a black hole party


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## Zubi-Ondo (Dec 9, 2008)

TheEndIsNigh said:


> Course we could just fire up the Hadron collider again and have ourselves a black hole party.




So I guess you were pretty disappointed when the collider didn't reverse the atomic spin on every atom in a 12,000 KM radius and send us all into oblivion then, huh? Don't worry TEIN, They're bound to come up with _something_ that will destroy the earth by accident eventually. The problem is, you may not live long enough to see it happen. There's always hope! 

 - Z.


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## TheEndIsNigh (Dec 9, 2008)

Oh I'll be there Z.

Forget not my motto:- in the short time we *ALL* have left


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## Zubi-Ondo (Dec 9, 2008)

Drachir said:


> I have a bit of a problem with the "pushing away" idea as well.  Anything that can push away the Earth almost certainly won't leave anything alive on it.



A blast as powerful as a super-nova would definitely have the energy to send all of the planets flying out into space. The problem is, it would most likely vaporize them all in a matter of seconds before they got "pushed" very far. Our sun is not big enough to go "super-nova". Our sun is in the 'G' category, and a star must be at least 8 times bigger than the Sun before it even has a chance of going super nova: 

Star classification - Scientia Astrophysical Organization

As far as the "shockwave" or "pushing" that we've talked about here is an example of it (read the text next to the picture):

NASA - Vivid View of Tycho's Supernova Remnant

 - Z.


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## Nik (Dec 9, 2008)

IIRC, the 'push' would not be solar pressure, which only works on *rather small* bodies, but due to reduction in Sun's mass while Earth/Moon pair's momentum is unchanged.

IMHO, other terrible ends include a 'dinosaur-killer' asteroid impactor, a crust-cracker 'dwarf planet' disturbed from eg Oort cloud, or a nearby supernova...

There's also a danger from middle-distance pulsars-- Not *eating* us, we seem to be well out of that zone but, if their beam crosses us, we're toast...

FWIW, the count of potentially hazardous 'low flying lumps' has jumped to 1010 after a long time around ~990...
SpaceWeather.com -- News and information about meteor showers, solar flares, auroras, and near-Earth asteroids


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## jojajihisc (Dec 10, 2008)

Nik said:


> IIRC, the 'push' would not be solar pressure, which only works on *rather small* bodies, but due to reduction in Sun's mass while Earth/Moon pair's momentum is unchanged.
> 
> IMHO, other terrible ends include a 'dinosaur-killer' asteroid impactor, a crust-cracker 'dwarf planet' disturbed from eg Oort cloud, or a nearby supernova...
> 
> ...



All good stuff. You're right about the radiation pressure not being the cause of a new orbit for Earth. A better way of thinking about it I should have considered is really a lack of being pulled quite so hard by the Sun with a decreased gravitational pull. It's an interesting idea though because while the Sun loses mass it is also potentially moving closer to Earth and gravity's force depends on both.

Another distant threat will be once the core of the Earth solidifies and the magnetosphere dwindles. Say hello sunblock with SPF 1,000,000,000 from the ultra-violet bath.

Gamma ray bursts certainly have the power to cleanse this planet of all life but it would apparently have to be pretty close.


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## TheEndIsNigh (Dec 10, 2008)

jojajihisc said:


> All good stuff. You're right about the radiation pressure not being the cause of a new orbit for Earth. A better way of thinking about it I should have considered is really a lack of being pulled quite so hard by the Sun with a decreased gravitational pull. It's an interesting idea though because while the Sun loses mass it is also potentially moving closer to Earth and gravity's force depends on both.
> 
> Another distant threat will be once the core of the Earth solidifies and the magnetosphere dwindles. Say hello sunblock with SPF 1,000,000,000 from the ultra-violet bath.
> 
> Gamma ray bursts certainly have the power to cleanse this planet of all life but it would apparently have to be pretty close.


 
Whoa there Joja, What is it about a solid core that removes it's magnetic qualities. It's mad of iron and will presumably freeze with a dominant N-S poles so it will still be a rotating magnetic field.

Anyway who cares, these time scales go well beyond the short time we all have left.


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## Karn Maeshalanadae (Dec 10, 2008)

I'm far more inclined to believe that neither nature nor an outside biological force will have anything to do with the end of the world. Humans are perfectly capable-and indeed, performing in-the destruction of this world, and I'm not just talking about the end of our race. Mining operations, bomb explosions, the wipeout of large amounts of plant and animal life.....


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## jojajihisc (Dec 11, 2008)

TheEndIsNigh said:


> Whoa there Joja, What is it about a solid core that removes it's magnetic qualities. It's mad of iron and will presumably freeze with a dominant N-S poles so it will still be a rotating magnetic field.
> 
> Anyway who cares, these time scales go well beyond the short time we all have left.


 
No, TheEndIsNigh iron itself is not why we have a magnetic field. It's not the material, the smaller, inner solid iron core that creates the field it is the moving, liquid outer core that generates an electric field as a giant dynamo. It is possible it could cool, much like we suspect happened on Mars and greatly weaken or bring to an end the geomagnetic field.


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## Nik (Dec 11, 2008)

IMHO, solidification may be delayed some-what as Earth/Moon tides keep the interior stirred...

Of course, the effect will diminish as tidal drag causes Moon to recede. IIRC, that drag is some-what dependent on continental drift opening / closing sea-ways etc, so impossible to accurately predict for far-future...

Basics From Wiki...

Tidal effects result in an increase of the mean Earth-Moon distance of about 3.8 m per century, or 3.8 cm per year.[52] As a result of the conservation of angular momentum, the increasing semimajor axis of the Moon is accompanied by a gradual slowing of the Earth's rotation by about 0.002 seconds per day per century.


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## Jimmy Magnusson (Dec 11, 2008)

Manarion said:


> I'm far more inclined to believe that neither nature nor an outside biological force will have anything to do with the end of the world. Humans are perfectly capable-and indeed, performing in-the destruction of this world, and I'm not just talking about the end of our race. Mining operations, bomb explosions, the wipeout of large amounts of plant and animal life.....



Life is too persistent to be wiped out by humans. If you don't believe me I'd recommend watching the second part of the BBC documentary The Blue Planet (The Deep). Likewise I don't believe that we humans will actually succeed in wiping ourselves out. We might take a hit or two that will start a downward decline, though. I think the most likely end for us will be evolution.

As for the end of the earth itself, that task will lay at the hands of the sun.


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## Delvo (Dec 15, 2008)

jojajihisc said:


> You're right about the radiation pressure not being the cause of a new orbit for Earth. A better way of thinking about it I should have considered is really a lack of being pulled quite so hard by the Sun with a decreased gravitational pull. It's an interesting idea though because while the Sun loses mass it is also potentially moving closer to Earth and gravity's force depends on both.


The near surface gets nearer, but the far surface gets farther, so that cancels out or comes pretty close to it. But also consider what happens with the surfaces around the "sides", where I've drawn the green lines in the attached image. With a bigger sun, those green lines are farther apart and slightly longer. (They're the hypotenuses of right triangles whose horizontal legs remain the same but whose vertical legs get longer.) That means two things:

1. Even though the size increase alone doesn't move the center farther away (and the near and far sides' movements toward and away from us cancel out) it does move the sides a bit farther away because of that more open angle. So the net overall effect is a bit of a shift of the mass away from us even without the sun moving. That weakens the gravitational attraction.

2. To follow this one, you must keep in mind that gravity doesn't just operate between two objects' centers alone; each object is attracted to the ENTIRE mass of the other one, every atom, including the very outermost edges. (For example, if you were anywhere inside a hollow spherical shell, you'd experience no net gravitational force, no matter how massive the shell was.) But attraction to mass at the "right" of the center and attraction to mass at the "left" of the center partially cancel each other out (the left and right components of their vectors add up to zero), so the only vector component which is experienced is the component that they have in common (straight toward the center). But the farther apart the right and left extremes are, the lower is the component of each one's independent gravity vector that points to the center, and the greater is the fraction that points right or left. So a greater fraction of the attraction to the edges gets canceled out by the opposite edge, and a lower fraction of it remains to attract you to the center. Thus, a more spread-out object has weaker gravity than a more compact one at the same distance (and the shorter the distance is, the bigger difference it makes).

So there are two ways that the sun's decrease in density reduces its gravity: by weakening the force itself regardless of distance, and by shifting mass farther away even without the objects themselves moving apart.

Both effects are actually more drastic than my illustration with the green lines shows. Right now, if we made an illustration accurate to scale, starting with the Earth the size of the head of a pin (a twelfth of an inch wide), the sun would be about 9 inches wide and more than 83 feet away. Just picture how big of a difference in the geometry it would make if that 9-inch object were to grow to roughly fill the 83 feet between them (so now it's a 166-foot diameter). The "before & after" for the real-world equivalent to my green lines would be more different than the image shows.



Manarion said:


> I'm far more inclined to believe that neither nature nor an outside biological force will have anything to do with the end of the world. Humans are perfectly capable


How? What specific method of doing so do you believe would be effective and is also within our ability?


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## TheEndIsNigh (Dec 15, 2008)

jojajihisc said:


> No, TheEndIsNigh iron itself is not why we have a magnetic field. It's not the material, the smaller, inner solid iron core that creates the field it is the moving, liquid outer core that generates an electric field as a giant dynamo. It is possible it could cool, much like we suspect happened on Mars and greatly weaken or bring to an end the geomagnetic field.


 
Now I'm no geologist Joja however, as I understand dynamos they rely on a magnetic material to be moved. Since the liquid outer core is just an amorphous mass rotating extremely slowly I don't quite get the mechanism that would cause it to be magnetic in a uniform manner such that it would generate a rotating field.

Whereas if the core is solid and therefore stable it would act like a permanent magnet if only a weak one. My personal view of the core is that it consists of several solid cores each magnetised in different polarisations. As these are shifted around the effective sum of the fields  explains the wobble of the north pole, the variance in intensity and the flip of the N/S poles


My theory about Mars is that the solidifying of it's core is why there is no surface water on the planet. Effectively the water has gone down the plug hole to fill the gaps.


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## Nik (Dec 15, 2008)

"... it consists of several solid cores..."

Um, seismology --and subtle 'shadowing' by liquid portions-- shows but one core, though the layers are nested like an onion...

IIRC, the technique is known as 'seismic tomography', and borrows some of the software tools used in medical imaging...

I remember the recent fuss when it was realised the Earth's 'inner core' might be rotating at a slightly different rate to the surface...

Here's a site you may find interesting:
Geology News | Earth Science Current Events | Geology.com


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