Could magnetic reversals be caused by meteorite or comet impacts?

Although extremely unlikely, it might be possible for a reversal of the Earth's magnetic field to be triggered by a meteorite or comet impact, or even for it to be caused by something more "gentle," such as the melting of the polar ice caps.

But self-contained dynamic systems like Earth’s dynamo can do this without any outside influence. Reversals of Earth's magnetic field can simply happen.

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Why measure the magnetic field at the Earth's surface? Wouldn't satellites be better suited for space-weather studies?

Satellites and ground-based magnetometers are important for making measurements of the Earth’s magnetic field. They are not redundant but are instead complementary. Satellites provide good geographical coverage for data collection. Ground-based magnetometers are much less expensive and much easier to install than satellites. An array of...

Does the Earth's magnetic field affect human health?

Not directly. High-altitude pilots and astronauts can experience higher levels of radiation during magnetic storms, but the hazard is due to the radiation, not the magnetic field itself. Direct effects on human health from the magnetic field at the Earth's surface are insignificant. Geomagnetism can impact the electrically-based technology that we...

Are we about to have a magnetic reversal?

Almost certainly not. Since the invention of the magnetometer in the 1830s, the average intensity of the magnetic field at the Earth's surface has decreased by about ten percent. We know from paleomagnetic records that the intensity of the magnetic field decreases by as much as ninety percent at the Earth's surface during a reversal. But those...

How does the Earth's core generate a magnetic field?

The Earth's outer core is in a state of turbulent convection as the result of radioactive heating and chemical differentiation. This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinetic energy is converted to electrical and magnetic energy. Basically, the motion of the electrically...

Do any mass extinctions correlate with magnetic reversals?

No. There is no evidence of a correlation between mass extinctions and magnetic pole reversals. Earth’s magnetic field and its atmosphere protect us from solar radiation. It’s not clear whether a weak magnetic field during a polarity transition would allow enough solar radiation to reach the Earth's surface that it would cause extinctions. But...

Is the Earth a magnet?

In a sense, yes. The Earth is composed of layers having different chemical compositions and different physical properties. The crust of the Earth has some permanent magnetization, and the Earth’s core generates its own magnetic field, sustaining the main part of the field we measure at the surface. So we could say that the Earth is, therefore, a "...

How can I tell if I have found an impact crater?

There are many natural processes other than impacts that can create circular features and depressions on the surface of the Earth. These include glaciation, volcanism, atolls, uplift, intrusions, and hydrothermal explosions (to name just a few). Prehistoric mines and quarries are also sometimes mistaken for impact craters. Although the USGS has...

Is it true that Earth's magnetic field occasionally reverses its polarity?

Yes. We can see evidence of magnetic polarity reversals by examining the geologic record. When lavas or sediments solidify, they often preserve a signature of the ambient magnetic field at the time of deposition. Incredible as it may seem, the magnetic field occasionally flips over! The geomagnetic poles are currently roughly coincident with the...
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Date published: March 8, 2018

New 3D Measurements Improve Understanding of Geomagnetic Storm Hazards

Measurements of the three-dimensional structure of the earth, as opposed to the one-dimensional models typically used, can help scientists more accurately determine which areas of the United States are most vulnerable to blackouts during hazardous geomagnetic storms.

Date published: September 12, 2016

Mapping a Space-Weather Menace to Electric-Power Grids

New strides have been made toward quantifying how geomagnetic storms can interfere with the nation’s electric-power grid systems.  

Date published: March 5, 2013

Iowa Meteorite Crater Confirmed

USGS Airborne Surveys Back Up Previous Decorah Research

Date published: October 24, 1998

Evidence Presented in Toronto... Meteorite Impact Formed Chesapeake Bay Impact Crater Controls Region’s Groundwater Flow and Quality

A large meteorite plummeted into the western Atlantic Ocean about 35 million years ago, creating the 120-km wide Chesapeake Bay impact crater [Geology (Boulder), 22 (8), p. 691-694].

Date published: June 12, 1998

Tiny Teeth Forecast Ancient Comet Showers

Minuscule fossil animal teeth, known as conodonts, indicate that a 370-million-year-old comet that slammed into southern Nevada could be as much as five times larger than scientists initially suspected.

Date published: March 20, 1998

Comet that triggered mass extinction was much larger than originally thought...

Minuscule fossil animal teeth, known as conodonts, indicate that a 370-million-year-old comet that slammed into Nevada could be as much as five times larger than scientists initially suspected.

Date published: October 20, 1997

Comet Struck Southern Nevada 370 Million Years Ago

An extraterrestrial object, theorized to be a comet at least one kilometer in diameter, impacted what is now southern Nevada about 370 million years ago.

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Mars Ice
December 31, 2018

Mars Ice

Mars Ice.

Chesapeake Bay Impact Crater Boundaries Map
September 26, 2016

Chesapeake Bay Impact Crater

Chesapeake Bay Impact Crater Boundaries Map

Image: Gale crater
March 14, 2016

Gale crater

Infrared mosaic image of Mars Gale crater by the Thermal Emission Imaging Spectrometer (THEMIS) of the USGS Astrogeology Science Center and Arizona State University. The Mars Science Laboratory is scheduled to land in Gale crater Aug. 5, 2012.

December 16, 2013

Hazards: Geomagnetic Storms

Space weather can have important consequences for our lives, such as interference with radio communication, GPS systems, electric power grids, the operation and orientation of satellites, oil and gas drilling, and even air travel as high altitude pilots and astronauts can be subjected to enhanced levels of radiation. It is also during magnetic storms that beautiful aurora

Attribution: Geomagnetism
October 16, 2007

Earth Science Week, Continued: Geomagnetism and the Self-Sustaining Dynamo Called Earth

USGS scientist Duane Champion explains the Earth's geomagnetic qualities and the potential for and possible consequences of a geomagnetic shift.

Image: Cratered cones near Hephaestus Fossae
June 7, 2007

Cratered cones near Hephaestus Fossae

Cratered cones near Hephaestus Fossae, Mars. This might look at first glance like a cinder cone, but it is more likely an impact crater. Using the shadow, one can tell that its floor is at a lower elevation than the surrounding landscape. A cinder cone would rise above the landscape. 

Cinder cones (otherwise known as scoria cones) are the most common type of volcano

March 22, 2007

PubTalk 3/2007 — Impact!

Piecing together the story of a giant meteorite crater beneath the Atlantic coast

By David S. Powars, Geologist, and R.D. Catchings, Geophysicist

  • Buried under Chesapeake Bay is a very well preserved impact structure 56 miles across and more than 2 miles deep
  • Following clues from drill holes and seismic imagery, careful
July 29, 2004

PubTalk 7/2004 — Secrets in Stone

The Role of Paleomagnetism in the Evolution of Plate Tectonic Theory Video Presentation

Presentation of the award-winning USGS video "Secrets in Stone" (35 minutes), introduced by Jack Hillhouse, Research Geophysicist, and followed by a tour of the USGS Paleomagnetics Laboratory

  • Crucial discoveries in the early 1960.s were made
Chart showing the Earth’s magnetic feild

Chart showing the Earth’s magnetic feild

This is one of five world charts showing the declination, inclination, horizontal intensity, vertical component, and total intensity of the Earth’s magnetic field at mean sea level at the beginning of 2005. The charts are based on the International Geomagnetic Reference Field (IGRF) main model for 2005 and secular change model for 2005-2010. The IGRF is referenced to the

The geomagnetic polarity timescale.

The geomagnetic polarity timescale

The geomagnetic polarity timescale.