Why the moon’s early magnetic field might be responsible for life on earth
Probing ancient magnetic fields
The new research investigates how the Earth’s and Moon’s early fields may have interacted. But probing these ancient fields isn’t easy. Scientists rely on ancient rocks that contain small grains that got magnetized as the rocks formed, saving the direction and strength of the magnetic field at that time and place. Such rocks are rare and extracting their magnetic signal requirescareful and delicate laboratory measurement.
Such studies have, however, unveiled that Earth has generated a magnetic field for at leastthe last 3.5 billion years, and possiblyas far back as 4.2 billion years, with a mean strengthjust over halfof the present-day value. We don’t know much about how the field was behaving any earlier than that.
By contrast, the Moon’s field was perhaps even stronger than Earth’s around 4 billion years ago, beforeprecipitously decliningto a weak field state by 3.2 billion years ago. At present, little is known about the structure or time-variability of these ancient fields, though.
Another complexity is the interaction between the early lunar and geomagnetic fields. The new paper, which modeled the interaction of two magnetic fields with north poles either aligned or the opposite, shows that the interaction extends the region of near-Earth space between our planet and the Sun that is shielded from the solar wind.
The new study is an interesting first step towards understanding how important such effects would be when averaged over a lunar orbit or the hundreds of millions of years that are important for assessing planetary habitability. But to know for sure we need further modelling and more measurements of the strengths of the Earth and Moon’s early magnetic fields.
What’s more, a strong magnetic field does not guarantee the continued habitability of a planet’s atmosphere – its surface and deep interior environments matter too, as do influences from space. For example, the brightness and activity of the Sunhas evolvedover billions of years and so has the ability of the solar wind to strip atmospheres.
How each of these factors contributes to the evolution of planetary habitability, and hence life, is still not fully understood. Their nature and how they interact with each other are also likely to change over geological timescales. But thankfully, the latest study has added another piece to an already fascinating puzzle.
This article is republished fromThe ConversationbyChristopher Davies, Associate Professor in Theoretical Geophysics,University of LeedsandJon Mound, Associate Professor of Geophysics,University of Leedsunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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