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The protective magnetic field shrouding the early Earth was likely only half as strong as it is today, a new study suggests.

The research also found that the Earth's magnetic field is 200 million years older than previously thought, which has implications for the amount of water that was originally present on the early Earth, and perhaps even on the development of life. Such a weak field in the Earth's early days may have also made for some spectacular auroras, or Northern Lights, at latitudes as low as what is now New York City, researchers said.

Earth's magnetic field is generated by the turbulent, convective motions of the planet's molten core. The field extends around the Earth for quite some distance into space until it meets the sun's incoming solar wind (the stream of charged solar particles constantly flowing away from the sun). The boundary where the two meet is called the magnetopause.

It is the magnetic field that protects the Earth's surface, and all of its inhabitants, from this energetic solar radiation, which would harm living organisms and strip away much of Earth's atmosphere (Mars has no significant magnetic field, which is thought to be the reason it has such a miniscule atmosphere).

But little is known about the magnetic field as it existed just after the Earth formed, around 4.5 billion years ago. To learn more about this early magnetic field, John Tarduno of the University of Rochester and his colleagues from the University of KwaZulu-Natal in South Africa, turned to the crystals in ancient rocks that preserve magnetic signatures.

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