The fate of the Earth?

Hi.

I saw this discussion:
http://www.sciforums.com/archive/index.php/t-41880.html

One poster posted:
"Well I'm about to finish the book on that. Venus has stopped spinning
by an internal mechanism that was feeded by chaotic resonance in its
orbit. Consequently the planet heated up tremendously melting it
completely. This happened one to two billion years ago. We still see
the residual heat of that process and this has nothing to do with
greenhouse gas effect.

There are many details supporting that hypothesis, like the shaping
and geologic frequencies of the plains indicating melting, the
exponential declining of volcanic activity indicates strong cooling
etc. The new paradigm rthat is currently emerging is "radiogenic heat"
and a lot of it. But what is the source. The most likely element -
potassium40- (40K) is also much more rare on Venus?

It was the big brake."

Is any of this good theory? If so, what sort of implication would it
have for the far future of the Earth, when the Sun's luminosity
increases to the point it begins to evaporate the oceans from the
globe? (Note that this happens quite far in advance of the red giant
phase.) As it seems to suggest things other than greenhouse are
necessary to get the Venus-like environment. If melting it down is
required to keep it so hot, not just greenhouse, then could it be that
the Earth might instead of becoming like Venus become more like Mars
with a depleted, thin and wispy atmosphere? Or is this bad theory?
It's been about 5 years since this was posted, so I suppose more work
has been done now on this subject.

mike3 wrote:
Hi.

I saw this discussion:
http://www.sciforums.com/archive/index.php/t-41880.html

One poster posted:
"Well I'm about to finish the book on that. Venus has stopped spinning
by an internal mechanism that was feeded by chaotic resonance in its
orbit. Consequently the planet heated up tremendously melting it
completely. This happened one to two billion years ago. We still see
the residual heat of that process and this has nothing to do with
greenhouse gas effect.

There are many details supporting that hypothesis, like the shaping
and geologic frequencies of the plains indicating melting, the
exponential declining of volcanic activity indicates strong cooling
etc. The new paradigm rthat is currently emerging is "radiogenic heat"
and a lot of it. But what is the source. The most likely element -
potassium40- (40K) is also much more rare on Venus?

It was the big brake."

Is any of this good theory? If so, what sort of implication would it
have for the far future of the Earth, when the Sun's luminosity
increases to the point it begins to evaporate the oceans from the
globe? (Note that this happens quite far in advance of the red giant
phase.) As it seems to suggest things other than greenhouse are
necessary to get the Venus-like environment. If melting it down is
required to keep it so hot, not just greenhouse, then could it be that
the Earth might instead of becoming like Venus become more like Mars
with a depleted, thin and wispy atmosphere? Or is this bad theory?
It's been about 5 years since this was posted, so I suppose more work
has been done now on this subject.


No, I don't think it's good theory. The Venus greenhouse was caused by a
lack of magnetic field. The lack of magnetic field was caused by Venus'
lack of rotation. Venus' lack of rotation was caused by god-knows-what.

I don't think there is any good theory as to what caused Venus to stop
spinning, although the favourite theory seems to suggest a resonance
with Jupiter caused it. But that doesn't explain why Earth and Mars
weren't affected, but why Mercury and Venus might have been.

Regarding Earth's greenhouse fate in the future. It's been suggested
that within 1 billion years, the Sun will be 10% hotter than it is
today, rendering habitation on Earth impossible. That ignores the fact
that the Sun was 10% cooler, 1 billion years ago too. The Earth adjusted
to the cooler Sun then, and it may very well adjust to the warmer Sun.
Certain theories suggest that lifeforms on Earth itself alter the
atmosphere enough to keep the planet habitable.

Yousuf Khan

On Sep 2, 10:55*pm, Yousuf Khan wrote:
mike3 wrote:
Hi.

I saw this discussion:
http://www.sciforums.com/archive/index.php/t-41880.html

One poster posted:
"Well I'm about to finish the book on that. Venus has stopped spinning
by an internal mechanism that was feeded by chaotic resonance in its
orbit. Consequently the planet heated up tremendously melting it
completely. This happened one to two billion years ago. We still see
the residual heat of that process and this has nothing to do with
greenhouse gas effect.

There are many details supporting that hypothesis, like the shaping
and geologic frequencies of the plains indicating melting, the
exponential declining of volcanic activity indicates strong cooling
etc. The new paradigm rthat is currently emerging is "radiogenic heat"
and a lot of it. But what is the source. The most likely element -
potassium40- (40K) is also much more rare on Venus?

It was the big brake."

Is any of this good theory? If so, what sort of implication would it
have for the far future of the Earth, when the Sun's luminosity
increases to the point it begins to evaporate the oceans from the
globe? (Note that this happens quite far in advance of the red giant
phase.) As it seems to suggest things other than greenhouse are
necessary to get the Venus-like environment. If melting it down is
required to keep it so hot, not just greenhouse, then could it be that
the Earth might instead of becoming like Venus become more like Mars
with a depleted, thin and wispy atmosphere? Or is this bad theory?
It's been about 5 years since this was posted, so I suppose more work
has been done now on this subject.

No, I don't think it's good theory. The Venus greenhouse was caused by a
lack of magnetic field. The lack of magnetic field was caused by Venus'
lack of rotation. Venus' lack of rotation was caused by god-knows-what.

I think you have that slightly sideways; as I understand it the
greenhouse stopped plate tectonics, vulcanism, and the core
circulation that creates a planetary magnetic field by eliminating
(well, strongly suppressing) the usual temperature differential
between the core and the surface.

But I agree the "theory" doesn't sound right either.

I don't think there is any good theory as to what caused Venus to stop
spinning, although the favourite theory seems to suggest a resonance
with Jupiter caused it. But that doesn't explain why Earth and Mars
weren't affected, but why Mercury and Venus might have been.

Worse, neither Venus nor Earth have large mascons like Earth's moon
and Mars do.

OTOH Venus' orbit is the most nearly perfectly circular of all the
planets. Since there are two glaring anomalies there, no spin and a
nearly perfectly circular orbit, it wold seem there's a connection,
but it sure isn't obvious.

Regarding Earth's greenhouse fate in the future. It's been suggested
that within 1 billion years, the Sun will be 10% hotter than it is
today, rendering habitation on Earth impossible. That ignores the fact
that the Sun was 10% cooler, 1 billion years ago too. The Earth adjusted
to the cooler Sun then, and it may very well adjust to the warmer Sun.
Certain theories suggest that lifeforms on Earth itself alter the
atmosphere enough to keep the planet habitable.

But then the Earth is also slowly fleeing the sun as its orbital
energy radiates away as (theoretical) gravitons.

Different timescales for all these processes though, and life can
only do so much if the sun gets bright enough to compensate for the
increasing distance.


Mark L. Fergerson

On Sep 3, 2:39*am, alien8er wrote:
On Sep 2, 10:55*pm, Yousuf Khan wrote:
No, I don't think it's good theory. The Venus greenhouse was caused by a
lack of magnetic field. The lack of magnetic field was caused by Venus'
lack of rotation. Venus' lack of rotation was caused by god-knows-what.

* I think you have that slightly sideways; as I understand it the
greenhouse stopped plate tectonics, vulcanism, and the core
circulation that creates a planetary magnetic field by eliminating
(well, strongly suppressing) the usual temperature differential
between the core and the surface.

The temperature at the surface of Venus is still nothing compared to
the temperature at the core. The Earth's core temperature is estimated
at between 5000-7000K, which would be presumably the estimate for
Venus' core temperature since they are of nearly the same mass. Venus'
surface temperature is only 750K.

Besides, it's highly unlikely that the atmosphere has enough power to
stop plate tectonics. It's not even clear if plate tectonics on Venus
has actually stopped as there seems to be volcanos on Venus, some of
which may or may not be active.

I don't think there is any good theory as to what caused Venus to stop
spinning, although the favourite theory seems to suggest a resonance
with Jupiter caused it. But that doesn't explain why Earth and Mars
weren't affected, but why Mercury and Venus might have been.

* Worse, neither Venus nor Earth have large mascons like Earth's moon
and Mars do.

I'll assume you were comparing Venus and _Mercury_ against Earth and
Mars. Mars' moons are nothing more than captured asteroids. They
aren't big enough to affect Mars' rotation. Mars' moons would actually
look insignificant next to Earth's Moon, and they could in fact easily
orbit the Moon as its own moons. Phobos, the biggest one, is only on
average 22 km in diameter, whereas the Moon is 3500 km. Mars diameter
is 6800 km, and Earth is 12800 km.

This one shows the relative size of the Moon versus the rocky planets
(but doesn't show Phobos or Deimos):

http://www.saintjoe.edu/~dept14/envi..._systems01.jpg

* OTOH Venus' orbit is the most nearly perfectly circular of all the
planets. Since there are two glaring anomalies there, no spin and a
nearly perfectly circular orbit, it wold seem there's a connection,
but it sure isn't obvious.

Here's a size comparison of what the Sun looks like at aphelion vs.
perihelion from Earth.

Astrophotography by Anthony Ayiomamitis
http://www.perseus.gr/Astro-Solar-Sc...Perihelion.htm

Regarding Earth's greenhouse fate in the future. It's been suggested
that within 1 billion years, the Sun will be 10% hotter than it is
today, rendering habitation on Earth impossible. That ignores the fact
that the Sun was 10% cooler, 1 billion years ago too. The Earth adjusted
to the cooler Sun then, and it may very well adjust to the warmer Sun.
Certain theories suggest that lifeforms on Earth itself alter the
atmosphere enough to keep the planet habitable.

* But then the Earth is also slowly fleeing the sun as its orbital
energy radiates away as (theoretical) gravitons.

That's not happening. The Earth won't move away from the Sun until the
Sun loses a significant amount of its mass, when it goes into its red
giant phase. The Sun might puff out a large amount of matter as a
planetary nebula at that point, and it would thus reduce in mass, thus
Earth would move away from it.

But losses due to gravitational friction don't happen until the two
bodies are significantly closer to each other. And those energy losses
would result in the Earth getting closer not further away.

* Different timescales for all these processes though, and life can
only do so much if the sun gets bright enough to compensate for the
increasing distance.

Life has already completely changed the entire composition of the
Earth's atmosphere. For example, prior to Life, there was no oxygen
molecules on Earth. Then the Great Oxidation Event made the Earth rich
in oxygen nearly 2.5 billion years ago.

The Rise of Oxygen
"Oxygen has not always been as abundant as it is today. Most
scientists believe that for half of Earth's 4.6-billion-year history,
the atmosphere contained almost no oxygen."
http://www.astrobio.net/exclusive/54...rise-of-oxygen

It is expected that Life will begin to pull greenhouse gases out of
the atmosphere and bury it into the sea or land, as the Sun heats up.
It's already happening now. Despite the mass hysteria about carbon
dioxide and global warming, the long term trend is actually that CO2
has been going down, not up.

Yousuf Khan

On Sep 3, 9:00*am, YKhan wrote:
On Sep 3, 2:39*am, alien8er wrote:

On Sep 2, 10:55*pm, Yousuf Khan wrote:
No, I don't think it's good theory. The Venus greenhouse was caused by a
lack of magnetic field. The lack of magnetic field was caused by Venus'
lack of rotation. Venus' lack of rotation was caused by god-knows-what.

On Sep 6, 1:54*am, alien8er wrote:

* If Venus were tidelocked due strictly to tidal deformation one would
expect, as I think you were implying, to see Mercury also perfectly
tidelocked.

* But we don't, and Mercury does have mascons:


Mercury is tidelocked so it rotates three times in the time that it
takes to go around the sun twice. This situation is fairly stable
because Mercury's orbit is quite eccentric (elliptical). When it is
near perihelion, its angular orbital velocity is about 1.5 times the
average, and that is the time when the tidal effect of the sun on it
is the greatest. So the tidal effect makes the rotation speed 1.5
times the average orbital speed. The mascons make this synchronization
exact.

However, tidal friction is occurring, which is slowly removing energy
from Mercury's orbit (without altering the total angular momentum),
with the result that the orbit is very slowly becoming more circular.
Eventually, unless the sun engulfs Mercury first, the 3:2 tidelock
will be broken, and Mercury's rotation will be slowed by tidal
friction until it is exactly synchronized with its orbital motion.

That's not happening. The Earth won't move away from the Sun until the
Sun loses a significant amount of its mass, when it goes into its red
giant phase. The Sun might puff out a large amount of matter as a
planetary nebula at that point, and it would thus reduce in mass, thus
Earth would move away from it.

* Whoops, can't believe I wrote that. Of course Earth is slowly
falling into the Sun.

I don't think so. The sun raises substantial tides on the earth
(about 1/3 as high as the tides that are raised by the moon), so tidal
friction is occurring that is transferring angular momentum from the
earth's rotation to its orbital motion. As a result, the earth is,
VERY slowly, moving away from the sun.

Also, the sun is losing mass as the solar wind takes material away
from it. This also causes the orbits of the earth and the other
planets to spiral outward. At present, this effect is very small, but
when the sun expands to become a red giant the solar wind will become
much stronger, causing more rapid spiralling.

dow

alien8er wrote:
On Sep 3, 9:00 am, YKhan wrote:
On Sep 3, 2:39 am, alien8er wrote:
I think you have that slightly sideways; as I understand it the
greenhouse stopped plate tectonics, vulcanism, and the core
circulation that creates a planetary magnetic field by eliminating
(well, strongly suppressing) the usual temperature differential
between the core and the surface.
The temperature at the surface of Venus is still nothing compared to
the temperature at the core. The Earth's core temperature is estimated
at between 5000-7000K, which would be presumably the estimate for
Venus' core temperature since they are of nearly the same mass. Venus'
surface temperature is only 750K.

From:

http://www2.ess.ucla.edu/~nimmo/website/paper25.pdf

"The generation of a global magnetic field requires core convection,
which in turn requires extraction of heat from the core into the
overlying mantle. Plate tectonics cools the Earth’s mantle; on the
basis of elastic thickness estimates and convection models, it is
argued here that the mantle temperature on Venus is currently
increasing. This heating will reduce the heat flux out of the core to
zero over ~1 b.y., halting core convection and magnetic field
generation. If plate tectonics was operating on Venus prior to ca. 0.5
Ga, a magnetic field may also have existed."

Understood, but a build-up of heat in the mantle of Venus wouldn't be
caused by Venus' greenhouse atmosphere. It would be caused by a crust
that is insulating it too much. The heat at mantle-crust junction might
be measured in the thousands of Kelvins, not in the hundreds of Kelvins
like at the crust-atmosphere junction.

It's assumed that a lot of heat in the Earth core is caused by Uranium
decay, thus there is a large source of heat still burning. If Venus'
nuclear core is finished, then it must've had much less Uranium than
Earth's does. So the question would be why the big difference in Uranium
between the two planets? If that is even the reason for it.

Besides, it's highly unlikely that the atmosphere has enough power to
stop plate tectonics. It's not even clear if plate tectonics on Venus
has actually stopped as there seems to be volcanos on Venus, some of
which may or may not be active.

There are a _lot_ of volcanoes on Venus, more than on any other
planet in our system:

http://volcano.oregonstate.edu/volca...nus/intro.html

The above page also, like many others, says there is _no_ evidence
Venus ever supported plate tectonics. I can find no cites saying it
ever did.

To me volcanoes would indicate an active crust. But then again, if the
crustal plates don't move around on Venus, then the volcanoes would be
the only way for heat to be released from the mantle. Volcanoes by
themselves can spew enough magma to create continents.

All of Venus' continents combined seem to be only large enough to fit
into Africa, which may be the result of lack of plate tectonics. Just
volcanic outcroppings turning into continents. If Venus had as much
water as Earth, it would be 90% water, and only the tops of volcanic
mountains would show through for the remaining 10%.

It's still early to tell whether there was any plate tectonics on Venus
or not. We'll really need to land there eventually to really know.

Worse, neither Venus nor Earth have large mascons like Earth's moon
and Mars do.
I'll assume you were comparing Venus and _Mercury_ against Earth and
Mars.

No. Tidelocking is usually assumed to be due mostly to tidal
deformation of the smaller body and resistant to dragging of the
resulting bulges, but the presence of mascons, as on Earth's Moon, can
rapidly accelerate the process.

So what you're talking about when you're talking about a "mascon" is a
"mass concentration"?

This one shows the relative size of the Moon versus the rocky planets
(but doesn't show Phobos or Deimos):

http://www.saintjoe.edu/~dept14/envi...5/solar_system...

Phobos and Deimos are both tidelocked to Mars. I don't know if we've
found mascons in either.

I think since neither of them are spherical moons, we can tell their
mascons simply by looking at their shapes.

That's not happening. The Earth won't move away from the Sun until the
Sun loses a significant amount of its mass, when it goes into its red
giant phase. The Sun might puff out a large amount of matter as a
planetary nebula at that point, and it would thus reduce in mass, thus
Earth would move away from it.

Whoops, can't believe I wrote that. Of course Earth is slowly
falling into the Sun.

Yeah, it probably won't have a chance to even fall into the Sun until
well after the Sun's expected lifespan.

I also don't agree with the Gaia hypothesis (or its variants) which
claim that life regulates the planet's surface environment to its
benefit. That, as far as I'm concerned, is largely blind luck on
life's part. Add enough energy and despite all the tricks life can do,
it will get baked out of existence, even the extremophiles.


Really? Why not? Some of the mildest versions of the theory are stating
nothing more controversial than that life evolves to take advantage of
the environment it's given, and second that life alters the environment
around it.

Yousuf Khan

"Yousuf Khan" wrote in message
...
mike3 wrote:
Hi.

I saw this discussion:
http://www.sciforums.com/archive/index.php/t-41880.html

One poster posted:
"Well I'm about to finish the book on that. Venus has stopped spinning
by an internal mechanism that was feeded by chaotic resonance in its
orbit. Consequently the planet heated up tremendously melting it
completely. This happened one to two billion years ago. We still see
the residual heat of that process and this has nothing to do with
greenhouse gas effect.

There are many details supporting that hypothesis, like the shaping
and geologic frequencies of the plains indicating melting, the
exponential declining of volcanic activity indicates strong cooling
etc. The new paradigm rthat is currently emerging is "radiogenic heat"
and a lot of it. But what is the source. The most likely element -
potassium40- (40K) is also much more rare on Venus?

It was the big brake."

Is any of this good theory? If so, what sort of implication would it
have for the far future of the Earth, when the Sun's luminosity
increases to the point it begins to evaporate the oceans from the
globe? (Note that this happens quite far in advance of the red giant
phase.) As it seems to suggest things other than greenhouse are
necessary to get the Venus-like environment. If melting it down is
required to keep it so hot, not just greenhouse, then could it be that
the Earth might instead of becoming like Venus become more like Mars
with a depleted, thin and wispy atmosphere? Or is this bad theory?
It's been about 5 years since this was posted, so I suppose more work
has been done now on this subject.


No, I don't think it's good theory. The Venus greenhouse was caused by a
lack of magnetic field. The lack of magnetic field was caused by Venus'
lack of rotation. Venus' lack of rotation was caused by god-knows-what.

I don't think there is any good theory as to what caused Venus to stop
spinning, although the favourite theory seems to suggest a resonance with
Jupiter caused it. But that doesn't explain why Earth and Mars weren't
affected, but why Mercury and Venus might have been.

Regarding Earth's greenhouse fate in the future. It's been suggested that
within 1 billion years, the Sun will be 10% hotter than it is today,
rendering habitation on Earth impossible. That ignores the fact that the
Sun was 10% cooler, 1 billion years ago too. The Earth adjusted to the
cooler Sun then, and it may very well adjust to the warmer Sun. Certain
theories suggest that lifeforms on Earth itself alter the atmosphere
enough to keep the planet habitable.

Yousuf Khan

Has tidal locking been ruled out in the case of Venus? Just curious.

George

George wrote:
Has tidal locking been ruled out in the case of Venus? Just curious.


Well, Venus tidally locking with the Sun has been ruled out, but there
is a possibility that Venus is tidally locked to Earth.

"For years it was thought that in the case of Venus that the Earth was
the culprit. It is a curious fact that as Venus rotates three times on
its axis in 729.27 days, the Earth goes twice around the Sun ( 728.50
days) This has suggested to many dynamicists that Earth and Venus are
locked into a 3:2 tidal resonance."
http://www.astronomycafe.net/qadir/q50.html

Yousuf Khan

On Sep 3, 11:24*pm, Yousuf Khan wrote:
George wrote:
Has tidal locking been ruled out in the case of Venus? *Just curious.

Well, Venus tidally locking with the Sun has been ruled out, but there
is a possibility that Venus is tidally locked to Earth.

"For years it was thought that in the case of Venus that the Earth was
the culprit. It is a curious fact that as Venus rotates three times on
its axis in 729.27 days, the Earth goes twice around the Sun ( 728.50
days) This has suggested to many dynamicists that Earth and Venus are
locked into a 3:2 tidal resonance."http://www.astronomycafe.net/qadir/q50..html

* * * * Yousuf Khan

The rotation speed of Venus is not *exactly* related to the orbital
period relative to the earth. If there were a tidal lock, we should
expect the periods to be exactly related.

The torque that the earth's gravity exerts on Venus is minuscule
compared with the torque that the sun exerts on it. The tidal torque
that the sun exerts is slowing down Venus's retrograde rotation.
Eventually, it will set Venus rotating in the prograde direction, and
will synchronize Venus's rotation with its orbital motion.

Probably, Venus used to rotate in the retrograde sense faster than it
does now. The sun is slowing the rotation, and we just happen to be
seeing it when it is roughly, but not exactly, synchronized with the
movements of the earth.

dow