I read somewhere recently that the magnetic poles of the earth were going to switch at some point in the future..is this correct, and if so what effects will this have..will gravity be affected?
The magnetic field of the Earth has actually switched its direction many many times during Earth's history. Although this is not completely understood, the leading theory of how it works is that Earth's magnetic field is caused by the motion of the liquid outer core. The churning of the liquid in the outer core acts as a giant electromagnet, moving electrical charges around, in what is known as the "geomagnetic dynamo." The rotation of the solid inner core also contributes to the magnetic field. When a certain combination of inner and outer core motion occurs, the Earth's magnetic field will quickly reverse. For example, lava that solidified 30,000 years ago shows that the magnetic field was in the opposite direction at that time. Evidence from the geologic record shows that this reversal could take less than 1000 or even less than 100 years. The way these reversals throughout geologic history were discovered was by looking at the seafloor. New ocean floor is created along the mid-ocean ridges. When lava along these ridges cools, its minerals harden in line with the Earth's magnetic field. This causes the seafloor to have magnetic "stripes," which can be measured and mapped. This is very useful for oceanographers and geologists. For a good explanation of this, check out this site.
Gravity is not affected at all by Earth's magnetic field, because gravity is the attractive force of the mass of two objects, which is unrelated to magnetism.
One effect that may occur during a magnetic reversal is that the Earth may not be protected from charged particles streaming from the sun. These particles are called the solar wind, and could be dangerous to life if they reached the Earth's surface. However, the interaction between the magnetic field and these particles deflects them around the Earth. The area around a planet (including Earth) within which the motion of charged particles is affected by the magnetic field is called the magnetosphere. Sometimes the magnetosphere becomes overloaded with particles. When this happens, some particles escape through the magnetosphere and interact with atoms in the upper atmosphere, making them emit light. This is what creates the northern lights (aurora borealis) and the southern lights (aurora australis). If the Earth's magnetic field is weakened during a reversal, more of these particles will get through to the upper atmosphere. This could be a problem, but most likely the atmosphere is thick enough to protect the Earth's surface.
Although the movie The Core tells the story of the Earth's magnetic field dissipating, causing the entire atmosphere to disintegrate, you don't need to worry about that happening! The magnetic field will exist as long as the outer core is liquid - and that will be for a long long time!
This page was last updated on June 27, 2015.