Scientists at the University of Rochester have discovered that the Earth’s magnetic field 3.5 billion years ago was only half as strong as it is today, and that this weakness, coupled with a strong wind of energetic particles from the young Sun, likely stripped water from the early Earth’s atmosphere.

The findings, presented in Science, suggest that the magnetopause — the boundary where the Earth’s magnetic field successfully deflects the Sun’s incoming solar wind — was only half the distance from Earth it is today.

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