Coastal & Marine Geology InfoBank

Home FACS Activities Atlas Geology School Related Sites More

USGS CMG InfoBank: Magnetic Reversals

Skip navigational links
Loading
Dictionaries: Our Mapping Systems   The USGS and Science Education   USGS Fact Sheets   Topics   Keywords   Data Dictionary   Metadata Dictionary   Computer Terminology   Digital Formats  
InfoBank Terms: Activity ID   activity overview   crew   digital data   formal metadata   lines   metadata   NGDC   port stops   project/theme   region   ship   stations   time   virtual globe   year  
Data Types: bathymetry   biological   geochemical   gravity   ground penetrating radar   imaging   LIDAR   logs   magnetics   metering equipment   navigation   samples   seismic   total station   definitions disclaimer  
Data Formats: ARC coverage   E00   FGDC metadata   gridded/image   imaging   material   scattered/swath   Shapefile   vector/polygon  
Comment: 21:33 - 22:12 (00:39)
Source: Annenberg/CPB Resources - Earth Revealed - 3. Earth's Interior
Keywords: "James Sadd", "magnetic field", "permanent magnetic field", magnetism

Our transcription: Although the Earth's magnetic field is similar to that of a bar magnet, there is one important difference.
The strength of the Earth's field varies considerably over time.
In fact, the Earth's field has decreased in strength about five percent over the last 150 years.
Rocks can also have a magnetic field, but their magnetism is permanent.
Iron rich rocks that have been strongly heated become magnetized by the Earth's magnetic field.
When the rock cools, that magnetism is locked in becoming a permanent part of the rock.
Because it's permanent, magnetized rocks of different ages are actually records of the Earth's magnetism throughout geologic time.

Geology School Keywords
Skip footer navigational links

Coastal and Marine Science Centers:  Pacific   St. Petersburg   Woods Hole  
InfoBank   Coastal and Marine Geology Program   Geologic Information   Ask-A-Geologist   USGS Disclaimer  


Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://walrus.wr.usgs.gov/infobank/programs/html/school/moviepage/03.01.29.html
Page Contact Information: InfoBank staff
Page Last Modified: Thu Oct 31 04:25:25 PDT 2013  (chd)