No, but gravity is almost zero at Earth’s centre. There, the only gravity is with the moon, other bodies in space and the effects of Earth’s asymmetrical shapes.
Gravity acts as a force of attraction between all things with mass. In the centre of Earth gravity cannot be perfectly equal in all directions; but for some practical purposes, gravity may be considered to be virtually zero in the centre. Gravity anomalies happen in the centre from the tidal effects of the Moon and the Sun. These effects are stronger, in Earth’s centre, than on the surface where they are masked somewhat by Earth’s gravity towards the centre of gravity, sometimes adding together, other times opposing each other, depending on the alignments of the Moon and the Sun. The Earth's true centre of zero gravity is also offset from the physical centre by variations in the density of areas within Earth, and according to variations from Earth shape being less than perfectly spherical.
Results of searches, relative to this writing, showed assumptions that have yet to be proven. For example, pressure in Earth's centre is assumed to be high; not because of there being nowhere else for hot liquid gas, plasma and expanding hot matter to go, but because of gravity being presumed to be maximum in the centre. Some reasoning still includes presumptions of gravity being maximum in the centre where in reality gravity at Earth's centre is virtually zero then it increases towards the half-way mark between the surface and the centre.
A traditional presumption is of the centre of Earth being molten iron. It happened, probably because of the misconception that gravity is generated at the centre rather than being a property of everything in the whole body of Earth. The superstition also relates to the belief that magnet properties are peculiar to iron despite iron losing magnetic ability at high temperatures. Similar authors can go so far as to draw the Earth’s magnetic field as a bar magnet with its north pole at the top of the planet, near the geographic North Pole. The magnetic North Pole is a south-seeking “pole”. [“North” for a magnet refers to being relatively North Pole seeking.] The Earth’s magnetic field is complex, far more than being like a simple bar-magnet; but at the surface it displays field characteristics similar to a bar magnet. Compass needles have to allow for the directions of magnetic fields as they aim into the Earth. Fields have direction relative to how other magnets would line up with them. Fields lines are drawn as North-South path lines, like isobars for equal magnetic stress or force, but rarely are the strengths of the fields represented other than by their distances apart (they're coded differently from height lines on ordinary maps).
In Earth’s centre, trapped plasma would be liquefied with some molten elements that are not gaseous. With everything being trapped in the centre they'd be under such high pressures and temperatures that even plasma would be different and have systems in it similar to solids and liquids. If Earth was not hot inside and if the centre could be bi-directionally vented to the surface, then the centre would be hollow with a vacuum; and at some level towards the surface, the inside surface could have an atmosphere (but not the same as at the surface, because life in the centre would have evolved without UV light for plants nor would such atmosphere have oxygen, unless the bacteria at the centre evolved to produce Oxygen and other gases on the surface as the result of living beings.
The Earth’s centre is most likely very hot. However, private correspondence showed that there is belief that no proof has happened for a certainty of the centre of Earth being hot, let alone molten. I propose the idea that in order to generate a magnetic field a planet must have a liquid flowing central area. Such liquid would have to be ionized enough to generate a magnetic field by it’s movements. The movements would not be random, because of the systematic influences of the gravity of the Sun and the Moon. To have a magnetic field the planet would also have to be spinning, with a difference between the rotation rates of the masses inside, relative to the rotation rates of the planet’s surface matter. For these reasons, I think the inside of the Earth is a highly ionized liquefied plasma of Hydrogen (H1 with an extra electron) and other elements in the plasma mix that, under huge pressures, would have unique properties as semi-solids, liquids and gasses rather than just a plasma mix. The mix is part of a living being, Earth, who produces a magnetic field system essential for other types of life with the Earth.
With the above idea in mind, for how the Earth’s magnetic field is produced, the field as seen at a distance is the sum of a hugely complex set of movements which, if they change their complexity only slightly, can scramble, null, reverse and make complex the field as seen from a distance. The Earth could sometimes have a number of extremely strong magnetic poles, rather than just the present weak apparently single pair of polarities.
Gravity, with the pressure caused by gravity, increases proportional to the distance from the centre towards a half-way band between the surface and the centre. At the half-way mark, there the pressure would be greatest; because anything in this area has gravity forces pressing down from both directions. From the top, gravity disallows the heaviest of matter from rising back to the top; and from the bottom, gas and plasma press because of both gravity and pressure, from below the half-way area towards the surface. By comparison, on the surface of the Earth, air pressure happens because of the weight of air above the surface. If there was zero gravity on Earth's surface, there would be no air and nothing to cause air pressure. Why the presumption of great pressure in Earth's centre caused by gravity? Great pressure could be happening in Earth's centre; but not because of gravity.
At the physical poles of Earth, gravity on the surface acts on everything and sinks anything heavier than air and water. Pieces of matter and liquids, by sinking, would accelerate towards the centre. They’d overshoot the maximum-gravity band then bounce around until friction changed the gravity-movement energy into heat.
The areas between the centre and the half-way area are likely to have liquid plasma, semi-molten and molten material moving following centrifugal and gravitational tendencies. Metals melt at temperatures in orders around 1,000°C, cool relative to temperatures that can happen in space. Earth's insides are likely a mix of solid, molten and semi-solid materials, all constantly circulating in compromises with gravity, rotational and centrifugal forces.
At the maximum-gravity band, about half-way below Earth’s surface, there centrifugal action would slightly reduce the weight of material with the greatest density — but not enough for the highest-density areas to get to the surface, not in our present times. When Earth was forming, its rate of spin could easily have been high enough to centrifuge the heaviest elements to the surface where they remain solidified or dissolved. By comparison, an object on the surface loses very little weight at the Equator, compared with the weight at the poles; even though the object is rotating at zero speed at the poles and approximately 1600Ks/hour (1,000mph) at the Equator. Centrifugal forces do help to sort dense objects from less-dense objects, so the band of maximum gravity would be slightly more towards the surface of Earth compared to where it would be if the Earth was not spinning.
By the way, has anybody done any calculations to estimate how far below the surface one has to go, towards the centre, before gravity changes to decreasing with depth down to zero at the centre? This "Elephant in the Room" is at least as large as any similar nonsense purporting to be science. The difficulties that people have, with the idea of zero gravity in Earth’s centre, are similar to the difficulties people had for changing from believing Earth was at the centre of the Solar System, that orbits were always perfect circles…changing to knowing the Sun is central and orbits are elliptical.
Why is the silly nonsense babbled on claiming that the Earth's core is "Iron"? Probably that happened many years ago when scientists forgot to test presumptions scientifically, because they could not do the tests, for so many generations that the presumptions changed into axioms. The same problems happen in modern times. Jargon, for describing conjecture and interesting proposals, can turn into unquestionable facts. More substances and plasma, liquid and solid systems, additional to Iron, can have organised magnetic fields.
In Earth's centre, some believe, there would be great heat; others maintain that there is no evidence of any heat within Earth other than that observed for causing volcanic evidence of heat at relatively very short distances from the surface.
The Earth's crust has lots of places where solid rocks insulate against heat; only up to tens of kilometres/miles thick, though. If there is great heat deep below the surface, the heat is prevented from being evident closer to the surface because of some surface rock layers being thick enough to insulate rocks closer to the surface. Heat on the surface is in an equilibrium where heat from the Sun escapes as fast as it gets to the surface. Any heat, from inside the Earth, is lost into space. The surface is cool enough to support life, presently. Below the surface, no heat from the Sun can reach and no heat from inside can reach, for many places on Earth. The deepest holes only go a very short distance into the Earth; not deep enough to reach the heat, and deep enough to observe averaged stable temperatures colder than at the surface (where the raised temperature is held in a minutely delicate balance, to support life). Some deep holes do not get hotter with depth; they get cooler; many get hotter only because of introduced heat being trapped because the rocks act as heat insulators. Other places on Earth are molten at the surface – volcanoes – and other places are molten a short distance from the surface.
There is evidence of heat, in deep mine shafts where there is no shallow geothermal heat. However, in places where geothermal activity is either absent below the surface, or so deep as to be ineffective, the only heat that heats up the shafts comes from mechanical activity and heat introduced from the surface. Some scientists regard evidence as absent, for great heat deep within the Earth. The existence of a magnetic field is easier to describe by allowing enough pressure and heat for ionized material to move in powerful electricity-causing circulations, with a net result including Earth’s present tiny magnetic field evidence.
Earth is most likely very hot in the centre. There, Hydrogen is likely to be dominant, because temperatures and pressures would disallow other material being formed by Hydrogen combining into more complex molecules. At temperatures and pressures as yet unknown, possibilities are that the cause of the internal heat is fusion, not fission and not just because Earth has not yet finished cooling in its cycle towards being a solid, hollow sphere.
Hydrogen is the lightest element but, when liquefied and unable to escape, Hydrogen so concentrated could build up a massive pressure --- massive enough to be more like solid Hydrogen than a gas, but... The Hydrogen is likely to be negatively ionized, H1 with an extra electron. Movement of this Hydrogen would have the same effect as moving electricity, causing the Earth's magnetic field phenomena.
Hydrogen is likely the basic building block of all substances. Hydrogen can be made with just two force field pieces sharing the same space to the exclusion of other force-field variations. If these oscillate fast enough, they can exclude everything else from their space. If the centre of Earth is hot plasma, then the H1 would be ionized or neutral building-block material. To have a magnetic field, the Earth inside would have to be a balance of H1 and Hydrogen plasma.
Animal, plant and microbial life are ok on Earth because of shielding, against radiation, caused by the Earth's magnetic field. The magnetic field happens for a planet only when there is a fine balance between solid, liquid and plasma happening from the centre towards the surface. In the centre, the plasma etc oscillate in time with the Moon and the Sun. Electrically conductive materials, in whatever combinations and conditions are needed for the phenomena, all contribute to the magnetic fields, because of their circulation patterns.
The Earth's magnetic field is composed of a complex system of circulating material moving at various speeds; slow at the surface up to faster rotations in the centre. The balances are fine enough to enable a reasonably stable overall weak magnetic field, as seen externally, in space, which forms a shield against otherwise deadly radiation from Space. Inside Earth the magnetic fields there are a hugely complex system. The sum of the magnetic field effects roughly correspond to the "North-South" description. Slight changes, in the complex circulation, can happen, like for a river that can change course; and the magnetic field balance can flip polarity for the summation of the various interacting magnetic field systems inside the Earth.
The Earth's internal tides would have some solid and semi-solid material denser than similar material it is mixed with. This solid material would circulate faster, because of centrifugal action of the Earth's rotation and because of being more dense and being near a pole. It would maximally reach the underside of the Earth's crust at the equator. There some would collide with the solid crust at the surface, wearing it away and making dents and pathways on the underside of the crust. The internal tides would follow paths like water-tides on the surface, to the poles, down towards the surface, then out, on average, towards the Equator. When near the poles, the heavier material would no longer have the Earth's centrifugal effects to keep it on the surface; so near and at the poles the material sinks until it reaches the layer of maximum gravity, which it overshoots. Depending on the relative density of the material, the overshoot intrudes towards the centre, and likely sometimes reaches the centre...unless at the centre the density of Hydrogen etc has increased enough to cause some intruders to float...
So what are we to make of the reasonable observation/proposal about gravity being zero in Earth's centre, for many practical purposes --- at least gravity as it is, by habit, usually considered? Internal matter circulations, caused by original rotation, and by the Moon and Sun, are probably the major contributors towards the Earth's magnetic field (along with the fact that the Earth is in orbit with the Sun and its charged outputs in the space around the planet). Rather than begin with many tiny pieces and try to find an overview from these, the situation is complex enough for one to like the idea of starting with known observations and deciding what is most likely necessary for these to be; even to the stage of considering the observations with new interpretations. An obvious fact is that life happens on Earth, and only within an infinitesimally small window of opportunity relative to the total lifespan of a planet. A magnetic field is essential for life; and a planet’s internal heat has to be at a delicate critical level for a magnetic field to provide an appropriate shield for life on the surface.
A clue, towards the origins of the Earth’s present shape, is in how the shapes of the continents show that they could have formed about half-way between the Earth's surface and the centre. They fit together well, if considered to have originally covered a sphere completely. That half-sized sphere would have been half the diameter of our Earth as it is, presently. Rather than think that perhaps the Earth used to be half it’s present size, what if the continents were formed within the band where gravity reverses — the above-proposed “half-way” levels. That layer would trap the heaviest materials. If, during Earth's formation, a stage was reached where the half-way shell cracked, then it could have centrifuged to the surface, to form the present continents that have been drifting slightly ever since.
Originally, when the system was a fast-spinning mix of gas and plasma, elements forming, from Hydrogen, would have been mixed in a somewhat homogeneous soup. The first-to-solidify materials, if heavier than the average, would have easily been centrifuged to the surface, to form the present continents. Likely, additional to the Moon and the Sun, the various densities and strengths of gravity, on the surface of the Earth, would help otherwise random electric forces to follow patterns enough to produce a magnetic field. The Earth is not perfectly round, leading to other gravity variations besides those attributable to a variety of densities. Centrifuge action does not explain how the continents could have fitted into a smaller sphere. Likely, they formed at the half-way point; perhaps a collision with a very dense object, molten, caused the formerly-heaviest objects to be floated-centrifuged to the surface where they have floated ever since, drifting around into the present arrangements of continents.
Continental drift causes and effects are still not proven enough to be considered to be axiomatic. Continental drift theories, as to causes, are explanations, not facts in their own right. Continental drift is still happening, did happen and will continue for some time until the Earth is perfectly solid. Continental drift and other causes have shaped the surface of Earth. Yes the shapes fit too well to be coincidental, but... Perhaps Earth had half itself busted off by a collision (Nubiru's moon, Nubiru herself? — a "Nubiru" barage of incoming weight-gain?). If the present stuff floating on the surface is less dense than the stuff underneath, then the present continental shapes could have just floated from their previous surface situation to a new, larger situation after the Earth gained twice its size because of a collision/collisions. Surface shapes have been redistributing over Earth surface, beginning as the cluster on the side furthest from the side that got busted, perhaps. Questions have to be answered about the density of matter under Earth's surface being more dense of less dense than the matter inside Earth. If less dense, then we may presume a cycle where the Earth's insides get so hot, because of having an insulative blanket, that the surface gets recycled regularly (leading to the idea that Earth is a few times older than its surface indicates).
© David Beale 2013 edited Sunday 23d March 2014