Evidence for the existence of Earth’s magnetic field has been pushed back about 250 million years, new research suggests.
Earth’s magnetic field was born by 3.45 billion years ago, a team including researchers from the University of Rochester in New York and the University of KwaZulu-Natal in South Africa report in the March 5 issue of Science. That date falls?during life’s earliest stages of development, between the period when the Earth was pummeled by interplanetary debris and when the atmosphere filled with oxygen. The researchers measured the magnetic strength of certain rocks found in the Kaapvaal craton of South Africa, a geologic region known to date back more than 3 billion years. The Greenstone Belt in South Africa had rocks that were just right: crystals of quartz less than two millimeters long with nanometer-sized bits of iron-containing magnetite embedded in them. Tarduno and his colleagues had studied similar rocks in 2007 and found that a magnetic field half as strong as today’s was present 3.2 billion years ago. To determine if the early magnetic field was enough to hold back the rain of radiation, the team needed to know what the sun was doing.
The amount of radiation regularly reaching Earth from the sun 3.45 billion years ago would be comparable to what rains down on the planet during the most powerful solar storms today, Tarduno says. The study “can be used to guide our searches for other life-bearing planets” as well, says astronomer Moira Jardine of the University of St. Despite the fact that no extrasolar planets with magnetic fields have ever been detected, Jardine and Tarduno remain optimistic. As the inner core cools, crystallizing iron releases impurities, sending lighter molten material into the liquid outer core.
In the last decade, seismic waves from earthquakes revealed the inner core looks like a navel orange, bulging slightly more on its western half.
Peter Olson and Renaud Deguen, geophysicists at Johns Hopkins University, set out to test this theory, called translational instability. Olson and Deguen found that adding inner-core asymmetry shifted magnetic north away from the center of the Earth, into the cooling hemisphere.

Geophysicist Bruce Buffett said Olson and Deguen's research is intriguing, but there are still questions about the underlying theory.
Magnetic Mayhem - Is Earth's fluctuating magnetic field responsible for recent spike in mass animal deaths? From warmest December on record to blizzards, wild winter sets records across the northeastern U.S. A bar magnet or a compass when hanged from their gravitational center, they come equilibrium at north-south pole direction of the earth. The field may therefore be old enough to have shielded some of the planet’s earliest life from the sun’s most harmful cosmic radiation. Several earlier studies had suggested that a magnetic field is a necessary shield against deadly solar radiation that can strip away a planet’s atmosphere, evaporate water and snuff out life on its surface. Using a specially designed magnetometer and improved lab techniques, the team detected a magnetic signal in 3.45-billion-year-old rocks that was between 50 and 70 percent the strength of the present-day field, Tarduno says. Tarduno and Eric Mamajek, an astronomer at the University of Rochester, used observations of young sunlike stars to infer how strong a solar wind the Earth was up against.
This quick rotation powered a strong magnetic field, which heated the sun’s atmosphere and carried away mass and angular momentum in a strong solar wind of charged particles. The aurora borealis, caused by solar wind particles accelerating along Earth’s magnetic field, would have been visible as far south as present-day New York City. It is surrounded by a liquid outer core (mostly iron and nickel), a rocky, viscous mantle layer and a thin, solid crust. This upwelling, combined with the Earth's rotation, drives convection, forcing the molten metal into whirling vortices. Geoscientists recently explainedthe asymmetry by proposing a convective loop: The inner core might be crystallizing on one half and melting on the other.
They ran numerical models simulating the forces that generate Earth's magnetic field, and included a lopsided inner core.

Magnetic particles trapped and aligned in rocks reveal that the magnetic north pole wandered around the Western Hemisphere over the past 10,000 years, and circled the Eastern Hemisphere before that - a result mirrored by the numerical test. Iron minerals record the strength and direction of the magnetic field that was present during their formation.
But you also have to have a magnetic field, because that protects the atmosphere from erosion and the complete removal of water.” Mars may be dry today because it lost its magnetic field early on, he adds. The team calculated that the point where the Earth’s magnetic field cancels out the solar wind would be only about five Earth radii above the planet’s center, less than half of the 10.7 radii it is today. Astronomers might want to focus more on older, less active stars or search for planets with their own magnetic fields, she says.
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The model does a good job at explaining some but not all of the features of the inner core," said Buffett, a professor at the University of California, Berkeley, who was not involved with the research. Gathering a longer, more detailed record of the magnetic field's behavior, Olson said, could reveal whether the inner core acts as researchers predict. But when rocks are heated in subsequent geological processes, they can lose or overwrite that record. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of Conde Nast.
Currently, the center of the field, called an axis, emerges in the Arctic Ocean west of Ellesmere Island, about 300 miles (500 kilometers) from the geographic North Pole. The reason for this magnetic field  is not explained yet however, most of the scientists believe that, earth's magnetic field looks like magnetic field of a bar magnet.

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