Earth's magnetic field
The Earth’s magnetic field is created by the rotation of the Earth and Earth's core. It shields the Earth against harmful particles in space. The field is unstable and has changed often in the history of the Earth. The magnetic field creates magnetic poles that are gradually moving toward the geographical poles. Many migratory animals use the magnetic poles when they travel long distances each spring and fall. The magnetic poles will trade places during a magnetic reversal.
Characteristics[change | change source]
The Earth’s geomagnetic field is created because of two things. The convective motions in the liquid conducting core inside the center of the Earth are important for making the magnetic field. When the convective motions occur with the electrical currents around the Earth, the magnetic field is created. The Earth’s rotation is what keeps the magnetic field up. The interaction between the convective motions and the electrical currents creates a dynamo effect.
The intensity of the magnetic field is greatest near the magnetic poles where it is vertical. The intensity of the field is weakest near the equator where it is horizontal. The magnetic field’s intensity is measured in gauss.
The magnetic field has decreased in strength through recent years. In the past twenty-two years, the field has decreased its strength 1.7%, on average. In some areas of the field, the strength has decreased up to 10%. The fast strength decrease of the field is a sign that the magnetic field might be reversing. The reversal might happen in the next few thousand years. It has been shown that the movement of the magnetic poles is related to the decreasing strength of the magnetic field.
A geomagnetic reversal is when the north magnetic pole and south magnetic pole trade places. The Earth’s magnetic poles have reversed a few times throughout the Earth’s history. The magnetic reversal happens after the strength of the field reaches zero. When the strength begins to increase again, it will increase in the opposite direction, causing a reversal of the magnetic poles. The time it takes the magnetic field to undergo a reversal is unknown, but can last up to ten thousand years. All of the Earth’s magnetic reversals are recorded in volcanic rocks also called basalt. Scientists believed that the last geomagnetic reversal occurred 780,000 years ago.
Magnetosphere[change | change source]
The magnetosphere is created by the magnetic field. It is the area around the Earth that acts as a shield against the harmful particles in solar wind. The magnetosphere has many different layers and structures, and solar wind shapes each of these layers. The interaction of solar wind and the magnetosphere also causes the Northern and Southern Lights to appear. The magnetosphere is very important in protecting the Earth against solar storms which increase solar wind activity. Solar storms can cause geomagnetic storms which sometimes have serious affects on the Earth.
The areas in between the north and south magnetic poles are the magnetic field lines. These lines leave the Earth from the vertical point of the South and reenters through the vertical point of the North. These two vertical points are called magnetic dip poles. The magnetic dip poles are commonly referred to as the magnetic poles. The magnetic poles intersect the earth at two points. The north magnetic pole intersects the Earth at 78.3 N latitude and 100 W longitude. This places the north magnetic pole in the Arctic Circle. The south magnetic pole intersects the Earth at 78.3 S latitude and 142 E longitude. This places the south magnetic pole in Antarctica. The magnetic poles are also where the magnetic fields are the strongest.
The magnetic poles have been shown to move locations. The north magnetic pole is moving much faster than the south magnetic pole. The movement of the north magnetic pole has increased its speed rapidly throughout recent years. Scientists predict that at the rate that the north magnetic field is moving, it will move and change locations from the Arctic Circle to Siberia. As the north magnetic pole gets closer to Siberia, it has an effect on the magnetic field. As the magnetic poles move the strength of the magnetic field decreases.
Migratory Animals[change | change source]
Animals that undergo long migrations depend on the magnetic field for a guide. The magnetic field is used for many things in these migratory animals. Migratory animals know their locations by the intensity of the field. They know the time because of circadian rhythms the field produces. Migratory animals are born with a magnetic map in their head that allows them to migrate great distances safely. Their ability to sense the magnetic field is because of magnetic particles. Other animals have a chemical compass based on a radical pair mechanism.
References[change | change source]
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- Scott, Rebecca, Robert Marsh, and Graeme C. Hays (March 2012). "A Little Movement Orientated to the Geomagnetic Field Makes a Big Difference in Strong Flows". Marine Biology 159 (3): 481-488.
- Wiltschicko, Wolfgang and Roswitha Witschko (August 2005). "Magnetic Orientation and Magnetoreception in Birds and Other Animals". Journal of Comparative Physiology 191 (8): 675-693.
- Lehikoinen, Aleksi and Kim Jaatinen (October 2011). "Delayed Autumn Migration in Northern European Waterfowl". Journal of Ornithology 153 (2): 563-570. http://www.cb.iee.unibe.ch/content/seminars__events/conservation_biology_journal_club/e7117/e7118/e8764/e9981/e9983/Lehikoinen_JOrn2011.pdf. Retrieved 26 February 2013.