• Are variations in the geomagnetic field somehow associated with earthquakes or vice versa?
    The USGS supports an important National Earthquake Hazards Program. As a small part of that effort there have been studies attempting to correlate magnetic variations, or more precisely, electro-magnetic variations, with earthquakes. Electro-magnetic v...

  • Could magnetic reversals be caused by meteorite or cometary impacts? Could reversals be caused by melting of the polar ice caps or some sort of planetary alignment?
    One of the most important jobs that a scientist has is to identify -- from among all the possible causes and effects in nature -- those that are the most important and strictly and necessarily causally related, and those that are simply insignificant and e...

  • Could the mass extinctions observed in the paleontological record be correlated with magnetic reversals?
    The magnetic field of the Earth does protect us from fast-moving charged particles streaming from the Sun, and so does the atmosphere. It is not clear whether or not the radiation that would make it to the Earth's surface during a polarity transition, ...

  • Do animals use the magnetic field for orientation?
    Yes. There is evidence that some animals, probably most notably sea turtles, have the ability to sense the Earth's magnetic field (although probably not consciously) and to use this sense along with their several other senses for purposes of navigation...

  • Does the Earth's magnetic field affect human health?
    Not directly. High-altitude pilots and astronauts can experience enhanced levels of radiation during magnetic storms, but the hazard is due to the radiation, not the magnetic field itself. Direct effects on human health from the magnetic field at the ...

  • How does a compass work?
    The needle of a compass is a small magnet that is allowed to pivot in the horizontal plane. The needle experiences a torque from the ambient magnetic field of the Earth. The reaction to this torque is the needle's preferred alignment with the horizon...

  • How does the Earth's core generate a magnetic field?
    Briefly, as the result of radioactive heating and chemical differentiation, the Earth's outer core is in a state of turbulent convection. This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinet...

  • Is it true that the magnetic field occasionally reverses its polarity?
    Yes. We know this from an examination of the geological record. When lavas deposited on the Earth's surface subsequently solidify, and when sediments deposited on ocean and lake bottoms solidify, they often preserve a signature of the ambient magneti...

  • Is the Earth a magnet?
    In a sense, yes. You probably know that the Earth is stratified. In radius it is composed of layers having different chemical composition and different physical properties. The crust of the Earth has some permanent magnetization, and the core of the Eart...

  • The strength of the magnetic field has been decreasing lately, does this mean that we are about to have a reversal?
    Almost certainly not. Direct historical measurements of the intensity of the geomagnetic field have been possible ever since Gauss invented the magnetometer in the 1830's. Since then the average intensity of the field at the Earth's surface has dec...

  • What about other magnetic fields, such as those from power lines, do they affect human health?
    This is a question more about health than geophysics; nonetheless, it is a question we are often asked.  The USGS is an earth science research agency, not a health agency, so we would refer you to the following authoritative articles and Web sites: ...

  • What are Aurorae?
    Aurorae is the plural of the word "aurora," which is a luminous glow of the upper atmosphere caused by energetic particles descending from the Earth's magnetosphere or coming directly from the Sun.  These energetic particles are mostly electro...

  • What are the hazardous effects of magnetic storms?
    The infrastructure and activities of our modern technologically-based society can be adversely affected by rapid magnetic-field variations generated by electric currents in the near-Earth space environment, particularly in the ionosphere and magnetosphere....

  • What causes the magnetic field to reverse its polarity?
    Nothing. That answer might surprise you, but the fact that the field occasionally reverses is simply a property of the continuous, on-going behavior of the Earth's dynamo. There is no "cause" per se.  With respect to the physics of the process...

  • What is a magnetic field?
    Fields fill the space between matter and they determine how it is that bits of matter can exert forces on other bits of matter at a distance.  There are several different fields in nature, and their reality is demonstrated by our observation of th...

  • What is a magnetic storm?
    A magnetic storm is a period of rapid magnetic field variation.  Briefly, magnetic storms have two basic causes: First of all, the Sun is always emitting a wind of charged particles that flows outward into space away from the Sun itself. Occasio...

  • What is a permanent magnet?
    Most material is non-magnetic, being composed of molecules made of atoms, each of which have electrons orbiting nuclear protons, where the motion of one electron, essentially a tiny electric current, generates a magnetic field that is cancelled by the ma...

  • What is declination?
    At most places on the Earth's surface, the compass doesn't point exactly toward geographic north. The deviation of the compass from true north is an angle called "declination." It is a quantity that has been a nuisance to navigators for centuries, ...

  • What is space weather?
    Space weather is the state of the environment in space near the Earth, including the solar wind and the Sun's magnetic field, the outer part of the Earth's magnetic field called the magnetosphere, and the electrically conducting part of the Earth&#...

  • Why do models and charts of the geomagnetic field need to be periodically updated?
    Models and charts of the magnetic field at the Earth's surface need to be periodically updated because the field is constantly changing in time.  The same fluid motion in the Earth's core that sustains the main part of the magnetic field als...

  • Why measure the magnetic field at the Earth's surface? Wouldn't satellites be better suited for space-weather studies?
    Satellites and ground-based magnetometers are important for making measurements of the Earth’s magnetic field. They are not redundant but are instead complementary. After executing several orbits of the Earth, satellites can provide good geographical...

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