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Author Topic: Tectonics....Why Only this Planet ?  (Read 12652 times)

Offline neilep

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Tectonics....Why Only this Planet ?
« on: 22/09/2004 19:31:53 »
I don't suppose this is an easy question to answer but I would be very interested in your theories (in plain english if poss please) as to why our humble blue marble of a planet is the only one in the solar system that currently has moving tectonic plates.

Thanks, your Down To Earth comments would be most welcome.

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« Last Edit: 22/09/2004 19:38:27 by neilep »


 

Offline Ylide

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Re: Tectonics....Why Only this Planet ?
« Reply #1 on: 23/09/2004 04:27:16 »
Aren't we the only planet that still has a fluid core?  I could be wrong here, astrogeology isn't my field.

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Offline gsmollin

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Re: Tectonics....Why Only this Planet ?
« Reply #2 on: 23/09/2004 04:55:55 »
The planet needs a hot core, and a cold crust to have plate tectonics. That's the heat engine. Most of the planets lack one or the other. The best possibilities are Venus and Mars, of course. I had thought that Venus does have plate tectonics. Its not like earth, lacking oceans, and its crust is at about 900 degrees Fahrenheit, which is hotter than some parts of the mantle here on earth. But the radar images show huge volcanoes, and apparent fault-lines. Venus is large enough to still have a hot core, so plate tectonics may still be active there. Seismometers would be tough on Venus. Maybe a remote sensing seismometer?
 

Offline neilep

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Re: Tectonics....Why Only this Planet ?
« Reply #3 on: 23/09/2004 09:22:51 »
According to my resources, Venus could be the nearest to be being like earth for tectonics but doesn't...(or doesn't now anyway)...but I understand that it's official (as far as can be seen today) that Earth is the only planet with moving plate tectonics.

Regarding the fluid core, this is what fuels the magnetic poles, as it's a prerequisite for it.

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Offline Titanscape

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Re: Tectonics....Why Only this Planet ?
« Reply #4 on: 27/12/2004 14:41:56 »
Venus is some places melts right through to the surface. But it has mountains, indicating tectonics. The moutains are thought to be capped in condensed shiny metal. The moon has mountains you can see with a telescope, but is cold inside now. I am sure I saw a volcano on Mars from Nasa. There is a volcano on one of Jupiter's satellites spuing up sulfur... Europa's surface is all new on a cosmic scale.

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« Last Edit: 27/12/2004 14:44:06 by Titanscape »
 

Offline rahonavis

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Re: Tectonics....Why Only this Planet ?
« Reply #5 on: 12/09/2005 13:16:28 »
The largest mountain known is a volcano on Mars called Olympus Mons. It's extinct, of course.
 

Offline daveshorts

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Re: Tectonics....Why Only this Planet ?
« Reply #6 on: 12/09/2005 14:37:04 »
I think I remember someone mentioning that water has quite a strong effect on tectonics, both altering what minerals form so their melting points and properties, and by directly lubricating the plate boundaries.

I don't know if this is an effect but wasn't the earth and the moon supposed to be formed by a large collision and the moon is made up of a lot of the lighter rocks that were thrown off... This would mean that the earth had relatively fewer light continental rocks, which may allow more of the planet to consist of ocean floors which are the working fluid for the convection currents that drive plate tectonics.  - warm ocean floor is created at the mid ocean ridges and cold ocean floor sinks in the subduction zones. Also the collision may have formed an asymmetry which you would need to start the convection....

 

Offline Simmer

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Re: Tectonics....Why Only this Planet ?
« Reply #7 on: 12/09/2005 20:44:12 »
I wonder if the Moon could have something to do with it - indirectly I mean through stirring up  the mantle material or tidally preventing divergent plate boundaries from healing up?
 

Offline David Sparkman

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Re: Tectonics....Why Only this Planet ?
« Reply #8 on: 18/09/2005 03:11:26 »
Venus would be a good example once we do some engineering, and drop most of the water out of the atmosphere. Just have to get the H2S04 to react with the surface rocks and be buried. Won't take much more than another billion years or so...

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Offline niko

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Re: Tectonics....Why Only this Planet ?
« Reply #9 on: 25/10/2005 19:51:28 »
what subject are we talking about?
 

Offline johndiver

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Re: Tectonics....Why Only this Planet ?
« Reply #10 on: 28/10/2005 04:51:41 »
re: cause of moving continents.
I understand the energy comes from movement of molten outer core. Someone else suggested that the weights of the Atlantic Ocean also contributes to the spreading of the Americas from Europe and Africa.
 

Offline daveshorts

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Re: Tectonics....Why Only this Planet ?
« Reply #11 on: 28/10/2005 13:11:53 »
I think you mean the mantle (the bit between the crust and the core making up the majority of the earth's mass), however I don't think this is the case.

Tectonics is driven by a convection current that includes the crust itself. Crust is fromed at the mid-ocean ridges which unsurprisingly is hot. This then spends a hundred million years or so cooling down, then is subducted. Because it is now cold and dense it sinks in the mantle pulling the plate along with it - the plates are also pushed slightly by the fact that mid-ocean ridges are hills so the plates tend to fall down them, but apparently the pull from the subduction is significantly stronger.

There are convection currents in the mantle, but these are not very related to the movements in plates - the upwellings are probably related to hot-spots, like the one that produces island chains like Hawaii (the hot spot stays still and the plate moves above it, forming a string of islands), and the one that is melting the continental crust causing the rift valley in Africa.
 

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Re: Tectonics....Why Only this Planet ?
« Reply #12 on: 29/10/2005 03:05:27 »
quote:
Originally posted by Simmer

I wonder if the Moon could have something to do with it - indirectly I mean through stirring up  the mantle material or tidally preventing divergent plate boundaries from healing up?



I was wondering if the moon might have had a very different effect.

One of the prime theories about the origin of our moon is that it was created by a collision between the Earth and a Mars sized planet, during the very early development of the solar system.  This collision stripped away a lot of the crust of the Earth, but very little of the core (this is suggested to explain why the moon has very little, if any, iron or other core material in it).

If this is the case, then it would seem to me logical to ask if maybe the remaining crust of the Earth is thinner than it might otherwise be, thus making it more likely to fracture.
 

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Re: Tectonics....Why Only this Planet ?
« Reply #13 on: 21/12/2005 17:42:08 »
Quote
Originally posted by neilep

I don't suppose this is an easy question to answer but I would be very interested in your theories (in plain english if poss please) as to why our humble blue marble of a planet is the only one in the solar system that currently has moving tectonic plates.

Thanks, your Down To Earth comments would be most welcome.

Hi Neilep,
what about icy moons such as Saturn's Enceladus ?:-
http://news.bbc.co.uk/2/hi/science/nature/4197686.stm
or Jupiter's moon Europa ?:-
http://www2.jpl.nasa.gov/galileo/images/europa/eurridge-fracture.html
They seem to have moving sheets of ice, analogous to Earth's plates of rock.
« Last Edit: 21/12/2005 17:50:42 by ROBERT »
 

another_someone

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Re: Tectonics....Why Only this Planet ?
« Reply #14 on: 22/12/2005 01:21:43 »
quote:
Originally posted by ROBERT
what about icy moons such as Saturn's Enceladus ?:-
http://news.bbc.co.uk/2/hi/science/nature/4197686.stm
or Jupiter's moon Europa ?:-
http://www2.jpl.nasa.gov/galileo/images/europa/eurridge-fracture.html
They seem to have moving sheets of ice, analogous to Earth's plates of rock.



The do appear to have some plate tectonics, but driven by the tidal pressures of their parent planet, not by internal heat dissipation.

Yes, the outcome is superficially similar, but the mechanism is totally different.  One particularly interesting difference is that the tidal mechanism seems to cause warm polar regions.
« Last Edit: 22/12/2005 01:24:21 by another_someone »
 

Offline Soul Surfer

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Re: Tectonics....Why Only this Planet ?
« Reply #15 on: 22/12/2005 09:08:53 »
I don't think there is a generally agreed reason abut there are quite a few theories but the origin and continued existance of our moon seems to be the most likely.  As others have said significant tidal distortion from the earth tides These were probably stronger in the past when the moon was closer the tidal friction of the more eapidly roatating earth is slowly pushing the moon away.  The origin of the moon as debris from a major collision probably stripped a significant amount of the earth's crust away and left it a bit short of crust so there's room for the bits of crust to move around on the mantle.  It also appears likely that the crust is in some sort of slow oscillations in which the contenents drift apart and then coalesce again into one supercontinent for a while and residual heat builds up under the large continent and eventually splits it apert violently.

This final bit seems to be the way that Mars and Venus work.  They appear to have full crusts so the suggestion is that heat from radioactivity and tidal friction builds up slowly under the criust and then breaks out violently every so often in the form of volcanic episodes and Mars in particular could have gone through green phases in the past when the atmosohere was denser and there was the chance of areas of liquid water on the surface as a result of this.

One thing that particularly interests me about this is how much is the presence of the moon and tides a helping factor in the evolution of life giving a drive to evolve by making conditions vary continuously and forcing life to cope with change.  OK the solar tides are about a quarter the size of the lunar ones and we would have ocean tides without the moon but they are fixed with respect to day and night the bigger lunar ones vary throughout the day.

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Offline neilep

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Re: Tectonics....Why Only this Planet ?
« Reply #16 on: 22/12/2005 18:43:21 »
Gosh...it's nice to see this thread revived.

Thank you Robert, another_someone & Soul Surfer for your recent contributions.

Those are great links Robert...thanks. That's a good point another_someone and that's food for thought Ian regarding the moon and evolution of life. What what have been the state of play with continetal drift and ocean tides all those millions of years ago ?...certainly the land mass was completely different.


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Offline hogeb

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Re: Tectonics....Why Only this Planet ?
« Reply #17 on: 08/02/2006 19:59:30 »
I actually took a course in graduate school called the Comparative Paleoclimatology of the Terrestrial Planets which centered on this very question.  In short, Venus is different from the earth because there is no water in its rocks.  Why there is no water is not understood, but without it plate tectonics screech to a halt.  Mars has had plate tectonics in its past, but doesn't now because its core has cooled.  There must be a heat engine to drive plate tectonics.  The fact that Mars is slightly cooler than the earth is thought to be the reason for its cooling, though it may be much more complicated than that.  Lord Kelvin once calculated the age of the earth by predicting how long it would take a molten planet to cool to the earth's current temperature and came up woefully short because he didn't account for radioactivity in the core and mantle.  I don't recall the rate of Mars cooling, but I seem to remember it took about two billion years for mars to cool.

Correct me if I'm wrong, anyone.

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Re: Tectonics....Why Only this Planet ?
« Reply #18 on: 08/02/2006 22:15:34 »
quote:
Originally posted by hogeb

I actually took a course in graduate school called the Comparative Paleoclimatology of the Terrestrial Planets which centered on this very question.  In short, Venus is different from the earth because there is no water in its rocks.  Why there is no water is not understood, but without it plate tectonics screech to a halt.  Mars has had plate tectonics in its past, but doesn't now because its core has cooled.  There must be a heat engine to drive plate tectonics.  The fact that Mars is slightly cooler than the earth is thought to be the reason for its cooling, though it may be much more complicated than that.  Lord Kelvin once calculated the age of the earth by predicting how long it would take a molten planet to cool to the earth's current temperature and came up woefully short because he didn't account for radioactivity in the core and mantle.  I don't recall the rate of Mars cooling, but I seem to remember it took about two billion years for mars to cool.




Sounds interesting.

I assume the correlation between water and plate tectonics is because water is used as a lubricant, but cannot other liquids be used for lubrication?

http://csep10.phys.utk.edu/astr161/lect/jovian_moons/ganymede.html
quote:

This represents the first conclusive evidence of plate tectonics in the Solar System beyond the Earth.



http://science.nasa.gov/newhome/headlines/ast29apr99_1.htm
quote:

On the Earth, the sea floor spreads apart slowly at mid-oceanic ridges as new crust flows up from Earth's hot interior. Meanwhile, the direction of Earth's magnetic field reverses occasionally, resulting in alternating stripes in the new crust that carry a fossil record of the past hundreds of million years of Earth's magnetic history, a finding that validated the once-controversial theory of plate tectonics.

"The discovery of this pattern on Mars could revolutionize current thinking of the red planet's evolution," said Dr. Jack Connerney of NASA's Goddard Space Flight Center, Greenbelt, MD, an investigator on the Global Surveyor's magnetometer team. "If the bands on Mars are an imprint of crustal spreading, they are a relic of an early era of plate tectonics on Mars. However, unlike on Earth, the implied plate tectonic activity on Mars is most likely extinct."

Alternate explanations for the banded structure may involve the fracturing and breakup of an ancient, uniformly magnetized crust due to volcanic activity or tectonic stresses from the rise and fall of neighboring terrain.


"In order to call this pattern a crustal spreading center like that observed in the mid-oceanic ridges on Earth, we need to find a point of symmetry, where the pattern on one side matches the pattern on the other. We have not yet found evidence of this type of symmetry,"



 

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Re: Tectonics....Why Only this Planet ?
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