Main Question or Discussion Point
How do we know the composition of the earth's core? In addition, what is the current model for the generation of Earth's magnetic field?
I'm curious to find out.
I'm curious to find out.
I think it is the other way around. The movie The Core got it wrong and it is actually the magnetic field that causes the spinning. Is that right?cause i remember that if that core stops rotating then we lose our magnetic field thus we lose the protection of the atmosphere..blablabla..all Guessing..
Yes there is, the formation of the inner core creates enough entropy to keep the geodynamo going, if it hadn't started to form we wouldn't have a magnetic field anymore.The dynamo, which in theory generates the earth's magnetic field, requires a sharp temperature differential at the core boundary (Core material crystallizing generates the sharp temperature differential but ...) The problem known as the "heat flux" problem is that based on thermodynamic calculations the maximum age of the earth's core is 1 billion years. As it is known that the earth's magnetic field has existed for at least 4.2 billion years, there is no mechanism to generate the sharp temperature differential which is required to create the thermal dynamic movement of conductive liquied core which is hypothesized to generate the geomagnetic field, prior to the formation of the earth's core.
Um. Like what? You're not confusing the magnetic field with gravity are you?if the earth's magnetism is due to revolving currrents, then this magnetism is basically something we've seen in motors and in so many other magnets...while these magnets attract only iron, howcome earth's magnetic field attracts every other object...
Okay, I'm slowly returning online after a large move and I'm not following this discussion, but that statement triggered something. WWe know that Heinrich event 1, the last one, timewise, is dated around 17-16,000 years ago, considering the sediment layering on the ocean floor. Now the Younger Dryas dates about 12,700 - 11,650 - not nearly the same. I have said before, we have no idea what the Younger Dryas was in the first place, A heinrich event seems rather unlikely......
See figure 9 in the paper that shows the geomagnetic field drops also correlates with abrupt climatic changes (for example Heinrich events, the Younger Dryas is an Heinrich event.)
From "Properties and Evolution of the Earth’s Core and Geodynamo" by Nimmo & Alfe
Page 15: “The limitations on dynamo models by current computer technology are sever. For instance, even with variable grid sizes, current models would need 10 times high radial resolution to capture the turbulent boundary layer (Glatzmaier 2002). The corresponding increase in computer power is unlikely to occur for at least a decade. As a result, the parameter space attainable with numerical models is a long way from that occupied by the real Earth. Current models have to either assume a core viscosity which is 10000 times too large, or a rotational timescale which is 10000 times too long (See Glatzmaier 2002). Perhaps surprisingly, despite these issues, several models have recently started to produce results which resemble the behavior of the earth’s field.”
Page 19: “At this point, it should be stressed that the model parameters adopted are in some cases a factor of 10000 different from those applicable to the Earth. The agreement between models and observations is thus somewhat surprising and suggests that Earth-like dynamos are possible over a large parameter space.”
For both the "Core Only" geomagnetic field hypothesis and the "Core forced by Ocean" geomagnetic hypothesis, "the resulting large scale magnetic field is eventually produced and maintained by the mechanism of inverse cascade, whereby the field growth at small scales is arrested through the back action of the Lorentz force on the flow, and magnetic energy is continuously transferred towards larger and larger scales, eventually concentrating at the largest scale allowed by the geometry of the flow" (Ryskin's comment, from source Frisch et al, Fluid Mech. 68, 769 (1975) & Firsch and Leorat, Fluid Mech. 77,321 (1976).Hi Billiards. In reply to your comment 16:
"Problems I foresee about saying this is the cause of earth's magnetism include: the atmosphere is not at all conductive therefore it is an unsuitable candidate as your fluid, the ocean on the other hand is conductive, but then how do you explain the dipolar nature of the field?"
I c..so if these two are different, y the emphasis is only on how magnetic fields are produced and not how gravitational fields are produced?? Also is there any way to create a gravitational field in a lab the way we create a magnetic field...?Um. Like what? You're not confusing the magnetic field with gravity are you?
How'd you work that one out? I would've thought power would've been a bit more suitable, the core generates somethin like 14 TWatts of heat. Don't really know how that fits into this debate, but it just makes more sense to me to talk about energy in relation to time.The problem, in the case of the earth is the energy of the geomagnetic field is 0.8 x 10^18 Joules which is roughly a 1000 times less than the estimated energy in the fluid-core (Ryskin's comment, from source Roberts and Glatzmaier, Rev. Mod. Phys. 72, 1081 (2000). Theoretically it is expected that the energy of driver and field are roughly equal, which is the case for the galaxy and other examples.
1. rapid? reversals really aren't that rapid, what, it's been something like 780 ka since the last one. (and besides, i don't believe either of us know enough about magnetohydrodyanamics to pursue this point - i don't see how your alternative hypothesis would solve this apparent problem (but maybe that's just me?))Phenomena to explain:
1. Very rapid and large geomagnetic field changes.
2. A reduction of the geomagnetic (75% of current level), followed by a slow increase to current level.
3. Magnesisferrite spinels (approx. 10 micrometers size) at minimums of the geomagnetic field. "The presence of ... magnesisferrite is ... a marker for ... a minimum in the intensity of the Earth's magnetic field". Preisinger et al. GSA Spec. Paper 356, page 213 (2002).
4. Superchron periods: Multi-million year periods when there is no reversal of the magnetic field.
5. Correlation of the planetary temperature and magnetic field level. (Which is affecting,
This, as far as I am concerned, is the standard model; everything you have contributed seems to fit quite nicely if you ask me.Studies based on measurements taken over the last 400 years, as well as paleo-magnetic measurements, have shown that the magnetic field of the Earth arises from three causes. First, the main field is associated with fluid motions in the core and varies spatially with wavelengths of thousands of kilometers and temporally on scales of years to millions of years. Second, an external field is produced by the interaction of the solar wind with ionized gas in the Earth's upper atmosphere. External variations range from global wavelengths to approximately 100 km and vary temporally on scales from less than a second to nearly 10 years....
Principles of Geophysics, Sleep & Fujita, Blackwell (1997)