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  #1121  
Old 29.06.2010, 10:09
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Re: Ask a Scientist

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Anyone care to hypothesise on what would cause the anomaly around Southern India on this map of the distribution of gravity around the Earth ?

I haven't the foggiest yet...


Looks like you discovered the entrance to the hollow earth.
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  #1122  
Old 29.06.2010, 10:50
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Re: Ask a Scientist

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Anyone care to hypothesise on what would cause the anomaly around Southern India on this map of the distribution of gravity around the Earth ?

I haven't the foggiest yet...]
A quick "back of a cigarette packet" calculation shows me that there's no more than 0.003% variation between the dark blue and dark red areas. So it' doesn't look like it's really an anomaly.

Note:- calculation based on a number of approximations and wild assumptions - one wild assumption being that I actually know what I'm looking at. Therefore ignore
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  #1123  
Old 29.06.2010, 10:58
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Re: Ask a Scientist

Hollow Earth, Flat Earth, surely a prank along the lines of the Jedi Church...

I was hoping for a more trekkified explanation such as a dark matter anomoly indicating a rift in the temporal zone caused by the explosion of a dark matter hyper drive of a crashed alien spaceship. That's my theory anyway
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  #1124  
Old 29.06.2010, 11:02
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Re: Ask a Scientist

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Hollow Earth, Flat Earth, surely a prank along the lines of the Jedi Church...
Vril seeker.
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  #1125  
Old 29.06.2010, 11:08
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Re: Ask a Scientist

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Hollow Earth, Flat Earth, surely a prank along the lines of the Jedi Church...
You'd think so wouldn't you, but I think there's some guy somewhere funding an expedition to the north pole to find the entrance, perhaps we should find him and tell him he's looking in the wrong place.

EDIT: Oh... Sadly, the guy died.

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I was hoping for a more trekkified explanation such as a dark matter anomoly indicating a rift in the temporal zone caused by the explosion of a dark matter hyper drive of a crashed alien spaceship. That's my theory anyway
That's in Cardiff.
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  #1126  
Old 29.06.2010, 11:11
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Re: Ask a Scientist

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Anyone care to hypothesise on what would cause the anomaly around Southern India on this map of the distribution of gravity around the Earth ?

I haven't the foggiest yet...

interesting map.
The anomality is around Sri Lanka which is also known as the "gem islands".
Sri Lanka has the highest density of gem deposits compared to its landmass. Ratnapura contains the most gem deposits and derived its name from the gem industry. Ratnapura means “city of gems”.

I guess that the nature of the geology and rocks of Sri Lanka can be a cause. Since the globe is not perfectly round but ellipsoid and is not homogeneous, this may cause "anomalities" ...but are probably not perceptible. Could it be that if you weight 70kg near iceland, that you probably weight 70.010kg in SriLanka?
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  #1127  
Old 29.06.2010, 11:24
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Re: Ask a Scientist

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Would it have anything to do with plate techtonics and India's fast movement away from Africa?
That's the best answer I've seen. It doesn't make sense for it to be a mantle source like a plume.
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  #1128  
Old 29.06.2010, 11:25
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Re: Ask a Scientist

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Weaker or lower ? Surely if the number of bonds is reduced then the chemical properties change and you no longer have water but a mass of potentially explosive gases.., however if the covalent bond becomes weaker, the viscosity, as you quote will reduce...
No. What I said - the average number of hydrogen bonds between the water molecules.

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  #1129  
Old 29.06.2010, 11:40
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Re: Ask a Scientist

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No. What I said - the average number of hydrogen bonds between the water molecules.

van der Waals forces
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  #1130  
Old 29.06.2010, 11:43
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Re: Ask a Scientist

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No. What I said - the average number of hydrogen bonds between the water molecules.

OK, a misread on my part slightly, so how would they decrease ? My argument leaning towards weakening rather than decreasing ??
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  #1131  
Old 29.06.2010, 11:46
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Re: Ask a Scientist

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interesting map.
TI guess that the nature of the geology and rocks of Sri Lanka can be a cause.
Most of the anomalies that you can perceive in this map are long-wavelength anomalies and not the result of local geology. IIRC, the seafloor at the lowest part of the Indian Ocean anomaly is 600 m lower than if it were isostatically supported. The lack of any noticeable plume signature argues that the cause is dynamic/mechanical in nature. I believe there has been some modeling to show this but it's been awhile since I've seen that literature.

The large anomalies near subduction zones (e.g. the western Pacific) are the result of dense/cold crustal/lithospheric material being subducted into the hot less dense mantle and flexural topography caused by the forces of subduction.
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  #1132  
Old 29.06.2010, 11:48
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Re: Ask a Scientist

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OK, a misread on my part slightly, so how would they decrease ? My argument leaning towards weakening rather than decreasing ??
If your mean free path between molecules is temperature dependent, and increases with temperature, the intermolecular forces should decrease/weaken (i.e. an inverse distance or distance^2 or distance^3 relationship).
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  #1133  
Old 29.06.2010, 11:50
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Re: Ask a Scientist

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Anyone care to hypothesise on what would cause the anomaly around Southern India on this map of the distribution of gravity around the Earth ?

As others have already suggested, plate tectonics. Comparing these two maps, all becomes much clearer... (the Indian plate is already known to be significantly thinner than its neighbours)

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  #1134  
Old 29.06.2010, 11:54
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Re: Ask a Scientist

But the tectonics / subduction zones etc are just a small fraction of the Earths surface compared to the whole shebang down to the core, and should not influence gravity to the degree shown in the map ? Or would it ? I agree that density plays a part in gravity here...
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  #1135  
Old 29.06.2010, 11:55
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Re: Ask a Scientist

Although the Filipino / Eurasia plate boundary is clearly visible on the map... Just the boundary...
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  #1136  
Old 29.06.2010, 12:01
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Re: Ask a Scientist

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But the tectonics / subduction zones etc are just a small fraction of the Earths surface compared to the whole shebang down to the core, and should not influence gravity to the degree shown in the map ? Or would it ? I agree that density plays a part in gravity here...
Yes, but there's a 1/r^2 relationship with buried anomalies so anything at the core mantle boundary needs to be pretty signficiant for it to register at the surface. What also matters is the density difference between source and surroundings. Thus, the cold lithosphere in the hot mantle near the surface is a much larger signal than many other things deeper in the mantle.

The real 'take away' here is that the anomaly map shows the contribution from many sources: density differences and dynamic topography at interfaces (be they at the surface, in the mantle, or at the core/mantle boundary). Some of the signal over the oceans is also due to dynamic topography caused by oceanographic circulation.
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  #1137  
Old 29.06.2010, 12:27
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Re: Ask a Scientist

Why are many of the continents, which are massive pieces of earth, sometime separated by a skinny stretch--i.e. North and South America at Panama, and where Spain meets Africa?
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  #1138  
Old 29.06.2010, 12:34
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Re: Ask a Scientist

Just my twopenneth, and clearly I'm no where near as informed as some of the quality posters on here, but no-body really knows what's inside the earth's core, right? As far as I know the russians have drilled the deepest, and even that is piddling compared to what's really there. Something possibly related, nobody can explain what causes the earths electromagnetic field, or why it flips every 100 000 years or so? Please correct me where I'm wildly innacurrate, but I think the general point is sounds.

So what's to stop there being something in the earths core that's significantly more dense around that region, possbly due to differences in pressure and geology (maybe related) that lends itself to all the other stuff described above?

If I'm talking complete rot, please, let me know
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  #1139  
Old 30.06.2010, 14:59
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Re: Ask a Scientist

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Why are many of the continents, which are massive pieces of earth, sometime separated by a skinny stretch--i.e. North and South America at Panama, and where Spain meets Africa?
It's just the way it is now. The western US is a pastiche of bits of contiental material and island arc material that's gotten pasted onto it over millenia.
The number and location and size of the continents changes with time, as does the total number of plates.
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  #1140  
Old 30.06.2010, 15:14
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Re: Ask a Scientist

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Just my twopenneth, and clearly I'm no where near as informed as some of the quality posters on here, but no-body really knows what's inside the earth's core, right?
Like 100%? No. But we have a pretty good idea given data from gravity, seismology, rotation of the earth, etc. These place pretty good bounds on things like density, elastic wave speeds, etc. It is estimated, from this and knowledge of Earth chemistry, that the core is mostly iron with some oxygen, sulfer, and some nickel. We also know that the outer core is liquid because it does not transmit shear waves. The inner core is known to be anisotropic, with a wave speed faster in the rotational direction, IIRC.

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As far as I know the russians have drilled the deepest, and even that is piddling compared to what's really there. Something possibly related, nobody can explain what causes the earths electromagnetic field, or why it flips every 100 000 years or so?
Well, we have a pretty good idea that it is caused by magnetohydrodynamic (MHD) motion in the Earth's outer core. The fact that terrestrial planets without liquid cores also have only nominal magnetic fields compared to ours, indicates we are on the right track. I've also seen full on 3D numerical simulations of MHD in the core and they do a reasonably good job of simulating that generation of the Earth's primary dipole field. Surprisingly enough, they also show a tendency to flip polarity.
I don't quite recall the physics of it but it may have been some interaction between the core field and the solid inner core and mantle. For various computational reasons, the simulations aren't really in the same parameter space for the Earth but it gives you an idea. I should go check up on this stuff myself. Geology has also shown that we can have a polarity reveral in as few as a few thousand years, perhaps less. That's when things could get interesting because you then don't have a nice magetic sheath protecting you from solar radiation, just a thin atmosphere. If we had the data, it would be interesting to know if mutation rates increased during these times throughout Earth history.

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So what's to stop there being something in the earths core that's significantly more dense around that region, possbly due to differences in pressure and geology (maybe related) that lends itself to all the other stuff described above?
Because, due to travel time data, we have pretty good bounds on density in the Earth. If there were something more dense down there, we'd know about it by now.
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