Shop Windows to the Universe

With Explore the Planets, investigate the planets, their moons, and understand the processes that shape them. By G. Jeffrey Taylor, Ph.D. See our DVD collection.

Interactive Animation of Seafloor Spreading and Magnetic Field Reversals

Earth's magnetic field reverses itself from time to time; North becomes South and South becomes North. Lava that cools and becomes rock at a given time in Earth's history stores a record of our planet's magnetic polarity at the time of the rock's formation. Rocks on the seafloor on either side of a mid-ocean spreading ridge preserve a record of the Earth's magnetic field over time. The discovery of this phenomenon was an important bit of evidence that helped confirm the theory of plate tectonics.

The interactive animation below illustrates this concept. Drag the compass, which represents a magnetometer, to the right and left. Can you find places where the magnetism of the rocks reverses? This section of seafloor is in the North Atlantic Ocean near Iceland. The rate of plate movement in this area is about 25 millimeters (1 inch) per year, or about 25 km (16 miles) every million years. Can you determine when the field reversals occurred?

Click the "Distance" checkbox to view a distance scale. Click the "Age" checkbox to see the age of the seafloor on either side of the ridge.

(Note: If you cannot see the animation below, or it is not working properly, you may need to download the latest Flash player.)

On this section of the seafloor, the history of Earth's magnetic field that is revealed includes the following periods:

  • Brunhes normal - present time to 730 thousand years ago
  • Matuyama reverse - 0.73 to 2.48 million years ago (ma)
  • Gauss normal - 2.48 to 3.40 ma
  • Gilbert reverse - 3.40 to 5.3 ma

If you want to build a physical model of this system, check out the seafloor spreading section of our "Magnetometer Extensions" activity.

Last modified March 29, 2004 by Randy Russell.

Shop Windows to the Universe Science Store!

Learn about Earth and space science, and have fun while doing it! The games section of our online store includes a climate change card game and the Traveling Nitrogen game!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Mid-Ocean Spreading Ridge

As the Earth cools, hot material from the deep interior rises to the surface. Hot material is red in this drawing, under an ocean shown in blue green. The hotter material raises the nearby layers, and...more

Plate Tectonics

Many forces change the surface of the Earth over time. The largest force that changes our planetís surface is movement of Earth's outer layer in a process called plate tectonics. As shown in this picture,...more

Volcanic Ash

Ash is formed as a volcano erupts when rocks made by the volcano blow apart into millions of tiny pieces. The rocks are still very hot, because they just formed from lava. If the hot rocks come into contact...more

Cinder Cones

Cinder cones are simple volcanoes which have a cone shape and are not very big. Compare the size of this volcano to the strato-volcano in this image. They are usually made of piles of lava, not ash. During...more

Flowing Lava

Lava can move in two ways, wide flat lava flows, or through channels which squeeze the lava into a small area. The fastest lava flows move at about 6 mi/hr, an easy jog, but they average between 2/3 and...more

How Do Plates Move?

Plates at our planetís surface move because heat in the Earthís core causes molten rock in the mantle layer to flow. We used to think the Earthís plates just surfed on top of the moving mantle, but now...more

Clues to Plate Movements

Many kinds of surface features are clues to a sliding lithosphere. Two types of features can form when plates move apart. At ocean ridges, the crust splits apart to make room for molten mantle rock. Continental...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA