Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

3.2 Billion-Year-Old Surprise: Earth Had Strong Magnetic Field

05.04.2007
Geophysicists at the University of Rochester announce in today's issue of Nature that the Earth's magnetic field was nearly as strong 3.2 billion years ago as it is today.

The findings, which are contrary to previous studies, suggest that even in its earliest stages the Earth was already well protected from the solar wind, which can strip away a planet's atmosphere and bathe its surface in lethal radiation.

"The intensity of the ancient magnetic field was very similar to today's intensity," says John Tarduno, professor of geophysics in the Department of Earth and Environmental Sciences at the University of Rochester. "These values suggest the field was surprisingly strong and robust. It's interesting because it could mean the Earth already had a solid iron inner core 3.2 billion years ago, which is at the very limit of what theoretical models of the Earth's formation could predict."

Geophysicists point to Mars as an example of a planet that likely lost its magnetosphere early in its history, letting the bombardment of radiation from the sun slowly erode its early atmosphere. Theories of Earth's field say it's generated by the convection of our liquid iron core, but scientists have always been curious to know when Earth's solid inner core formed because this process provides an important energy source to power the magnetic field. Scientists are also interested in when Earth's protective magnetic cocoon formed.

But uncovering the intensity of a field 3.2 billion years in the past has proven daunting, and until Tarduno's research, the only data scientists could tease from the rocks suggested the field was perhaps only a tenth as strong as today's.

Tarduno had previously shown that as far back as 2.5 billion years ago, the field was just as intense as it is today, but pushing back another 700 million years in time meant he had to find a way to overcome some special challenges.

The traditional approach to measuring the ancient Earth's magnetic field would not be good enough. The technique was developed more than four decades ago, and has changed little. With the old method, an igneous rock about an inch across is heated and cooled in a chamber that is shielded from magnetic interference. The magnetism is essentially drained from the particles in the rock and then it's refilled while scientists measure how much the particles can hold.

Tarduno, however, isolates choice, individual crystals from a rock, heats them with a laser, and measures their magnetic intensity with a super-sensitive detector called a SQUID—a Superconducting Quantum Interface Device normally used in computing chip design because it's extremely sensitive to the tiniest magnetic fields.

Certain rocks contain tiny crystals like feldspar and quartz—nano-meter sized magnetic inclusions that lock in a record of the Earth's magnetic field as they cool from molten magma to hard rock. Simply finding rocks of this age is difficult enough, but these rocks have also witnessed billions of years of geological activity that could have reheated them and possibly changed their initial magnetic record.

To reduce the chance of this contamination, Tarduno picked out the best preserved grains of feldspar and quartz out of 3.2 billion-year-old granite outcroppings in South Africa. Feldspar and quartz are good preservers of the paleomagnetic record because their minute magnetic inclusions essentially take a snapshot of the field as they cool from a molten state. Tarduno wanted to measure the smallest magnetic inclusions because larger magnetic crystals can lose their original magnetic signature at much lower temperatures, meaning they are more likely to suffer magnetic contamination from later warming geological events.

Once he isolated the ideal crystals, Tarduno employed a carbon dioxide laser to heat individual crystals much more quickly than older methods, further lessening the chance of contamination. With the University's ultra-sensitive SQUID he could measure how much magnetism these individual particles contained.

"The data suggest that the ancient magnetic field strength was at least 50 percent of the present-day field, which typically measures 40 to 60 microteslas," says Tarduno. "This means that a magnetosphere was definitely present, sheltering the Earth 3.2 billion years ago."

To further ensure his readings were accurate, Tarduno also checked the alignment of the magnetism in the particles, which record the polarity of the Earth's field at that time and location. By comparing the polarity to that of other samples of similar age and location, Tarduno could ensure that his measurements were not likely from later geological heating, but truly from 3.2 billion years ago.

Tarduno is now pushing back in time to 3.5 billion-year-old rocks to further investigate when the Earth's inner core first formed, giving new insights into early Earth processes that also may have had an effect on the atmosphere and the development of life on the planet.

Rory Cottrell, post-doctoral student in Tarduno's laboratory, is co-author on the study. This research was funded by the National Science Foundation.

About the University of Rochester

The University of Rochester is one of the nation's leading private universities. Located in Rochester, N.Y., the University gives students exceptional opportunities for interdisciplinary study and close collaboration with faculty through its unique cluster-based curriculum. Its College of Arts, Sciences, and Engineering is complemented by the Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser Energetics, Schools of Medicine and Nursing, and the Memorial Art Gallery.

Jonathan Sherwood | EurekAlert!
Further information:
http://www.rochester.edu

More articles from Earth Sciences:

nachricht Large-Mouthed Fish Was Top Predator After Mass Extinction
26.07.2017 | Universität Zürich

nachricht Strength of tectonic plates may explain shape of the Tibetan Plateau, study finds
25.07.2017 | University of Illinois at Urbana-Champaign

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Physicists Design Ultrafocused Pulses

Physicists working with researcher Oriol Romero-Isart devised a new simple scheme to theoretically generate arbitrarily short and focused electromagnetic fields. This new tool could be used for precise sensing and in microscopy.

Microwaves, heat radiation, light and X-radiation are examples for electromagnetic waves. Many applications require to focus the electromagnetic fields to...

Im Focus: Carbon Nanotubes Turn Electrical Current into Light-emitting Quasi-particles

Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers

Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...

Im Focus: Flexible proximity sensor creates smart surfaces

Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.

At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...

Im Focus: 3-D scanning with water

3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects

A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

 
Latest News

Programming cells with computer-like logic

27.07.2017 | Life Sciences

Identified the component that allows a lethal bacteria to spread resistance to antibiotics

27.07.2017 | Life Sciences

Malaria Already Endemic in the Mediterranean by the Roman Period

27.07.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>