Geomagnetic reversal facts for kids
Dark areas = periods where polarity matches the present
Light areas = periods where polarity is reversed
Imagine the Earth's giant magnet flipping! A geomagnetic reversal happens when the Earth's magnetic field changes direction. This means the magnetic north and magnetic south switch places.
This has happened many times in Earth's history. Scientists know this by studying rocks on the sea floor. When hot lava cools, tiny magnetic bits inside it point to where the Earth's magnetic field was at that time. It's like a natural compass frozen in rock!
These periods of stable magnetic direction are called chrons. There is no clear pattern to when these flips happen. They seem to occur randomly. Chrons can last from 100,000 years to 1 million years. Most reversals take between 1,000 and 10,000 years to fully happen.
The last big flip, called the Brunhes–Matuyama reversal, happened about 780,000 years ago. It might have happened quite quickly, even within a human lifetime. There was also a shorter event called the Laschamp event about 41,000 years ago. This brief flip lasted only about 440 years. During this time, the magnetic field became very weak, only 5% of its strength today. Shorter changes that don't lead to a full reversal are called geomagnetic excursions.
Contents
Reading Earth's Magnetic History
Scientists first learned about past geomagnetic reversals by looking at magnetic stripes on the ocean floor. This discovery helped create the theory of plate tectonics. As the sea floor slowly spreads apart, new basalt rock forms. This rock records the Earth's magnetic field at that time. It creates "stripes" of normal and reversed magnetism.
Scientists can find this information by dragging a special tool called a magnetometer along the sea floor. Since no ocean floor is older than about 180 million years, other methods are used for older reversals. Many sedimentary rocks have tiny amounts of iron-rich minerals. These minerals line up with the magnetic field when the rock forms. The rocks keep this record unless they are changed later.
Super-Long Magnetic Periods
A superchron is a very long period when the Earth's magnetic field stays in one direction for at least 10 million years. There are two main superchrons that we know about.
The Cretaceous Normal superchron lasted for almost 40 million years. During this time, the magnetic field was always in the "normal" direction, like it is today. After this superchron, the magnetic field started flipping more often.
The Kiaman Reverse superchron was even longer. It lasted for more than 50 million years, from about 312 to 262 million years ago. During this entire time, the Earth's magnetic field was reversed. The name "Kiaman" comes from a village in Australia where early evidence of this superchron was found.
What Causes Magnetic Flips?
The Earth's magnetic field comes from a "dynamo" effect. This happens because of the movement of hot, molten iron in the Earth's core. This movement creates electric currents, which then make magnetic fields.
Scientists use computer simulations to understand this process. For example, some scientists created a model that showed how the Earth's magnetic field works over 40,000 years. Their computer model actually showed the magnetic field reversing itself! This suggests that reversals are a natural part of how the Earth's core works.
Effects on Life
As far as we know, geomagnetic reversals do not have any major effects on life. Scientists have studied if these flips are connected to extinction events. However, studies show no clear link between magnetic reversals and times when many species died out.
Images for kids
-
NASA computer simulation using the model of Glatzmaier and Roberts. The tubes represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth's core.
See also
In Spanish: Inversión magnética para niños
