Reversals of Earth's Magnetic Field During the Past 160 Million Years
This image shows the reversals of Earth's magnetic field over the past 160 million years. The changing polarity of Earth's magnetic field over time is indicated by the black and white stripes along the bottom of the timeline. Periods of "normal" magnetic polarity (when the field was oriented in the same direction as it is now) are shown as black; times of reversed polarity are shown in white. This timeline runs from 160 million years ago in the Jurassic Period (far left) to the present day (far right). |

The "pattern" of reversals is anything but regular. During one span of more than 40 million years in the Cretaceous Period the magnetic field's polarity remained unchanged. At other times, the field has flipped back and forth several times within a million years.
Earth's magnetic field has been in its current alignment, called the Brunhes normal, for the past 780,000 years. Click here for a closer look at magnetic reversals over the most recent 5 million years, or here to see the 5 million year and 160 million year timelines side-by-side. |
You might also be interested in:

The force of magnetism causes material to point along the direction the magnetic force points. This property implies that the force of magnetism has a direction. As shown in the diagram to the left, the
...more
Looking for online content that can be used for a climate change education course or module? Pages linked below can be used to support an introductory climate change education for either a unit or a full
...more
The Earth has a magnetic field with north and south poles. The magnetic field of the Earth is enclosed in a region surrounding the Earth called the magnetosphere. As the Earth rotates, its hot core generates
...more
The belts of trapped radiation above the Earth's atmosphere, but within the magnetosphere, were first detected by James Van Allen in 1958. Therefore these belts are also known as Van Allen Belts. When
...more
Earth has a magnetic field. If you imagine a gigantic bar magnet inside of Earth, you'll have a pretty good idea what Earth's magnetic field is shaped like. Of course, Earth DOESN'T have a giant bar magnet
...more
Earth has a global magnetic field that is approximately, though not exactly, a dipole field (like a bar magnet) with a north pole and a south pole. Earth's North Magnetic Pole (NMP) is not in the same
...more
Altocumulus clouds (weather symbol - Ac), are made primarily of liquid water and have a thickness of 1 km. They are part of the Middle Cloud group (2000-7000m up). They are grayish-white with one part
...more