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
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
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
Shop Windows to the Universe Science Store!
Our online store
includes issues of NESTA's quarterly journal, The Earth Scientist
, full of classroom activities on different topics in Earth and space science, as well as books
on science education!
You might also be interested in:
As the Earth cools, hot material from the deep interior rises to the surface. Hot material is depicted in red in this drawing, under an ocean shown in blue green. The hotter material elevates the nearby...more
The main force that shapes our planetís surface over long amounts of time is the movement of Earth's outer layer by the process of plate tectonics. This picture shows how the rigid outer layer of the...more
Ash is made of millions of tiny fragments of rock and glass formed during a volcanic eruption. Volcanic ash particles are less than 2 mm in size and can be much smaller. Volcanic ash forms in several ways...more
Cinder cones are simple volcanoes which have a bowl-shaped crater at the summit and only grow to about a thousand feet, the size of a hill. They usually are created of eruptions from a single opening,...more
Lava can move in broad flat lava flows, or it can move through tight channels or tubes. Lava flows tend to cool quickly and flow slowly. The fastest lava outside of channels moves at about 6 mi/hr an easy...more
Plates at our planetís surface move because of the intense heat in the Earthís core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when...more
Many kinds of surface features are clues that our lithosphere is sliding. Two types of features can form when plates move apart. At mid ocean ridges, the bottom of the sea splits apart and new crust is...more