Young Earth was cocooned in a protective shield that magnetically deflected killer solar radiation 200 million years earlier than previously thought, a key factor that allowed life to take hold, according to a new study published this week in the journal Science.
The research, based on analysis of ancient silicate crystals from South Africa, has implications for the search for life beyond Earth, which to date has focused on finding planets where liquid water can exist.
The study by University of Rochester geophysicist John Tarduno and colleagues suggests that the ability of a planet to generate a large magnetic field also is important for developing life, as it provides a shield against high-energy radiation from the parent star.
"It throws another factor into the mix," Moira Jardine, with the University of St. Andrews in the United Kingdom, told Discovery News. "In order to support life, we think that planets need liquid water on their surfaces, and that means they need to be at the right distance from their star — not too hot, not too cold. But, they also need to have a magnetic field strong enough to shield their atmosphere."
"The 'strong enough' is important, because it's a balance between the planet's magnetic field and the wind from the star the more powerful the stellar wind, the stronger the magnetic field the planet needs," she added.
As stars age, their spin rates slow, causing their winds to die down, so it may be better to look for habitable planets around older stars, Jardine said.
Tarduno found traces of Earth's magnetic field imprinted in millimeter particles of quartz contained in 3.5-billion-year-old igneous rocks, a discovery that puts the existence of a planetary magnetic field at 3.45 billion years ago 200 million years earlier than previously thought and possibly before life arose on Earth.
When life first appeared remains hotly debated, but the presence of a magnetic field means that more of the early planet's water and atmosphere was protected, Tarduno said.
"In one sense, (the magnetic shield) protected the Earth from wholesale erosion of the atmosphere and the oceans, but there probably was some modification of the atmosphere and the oceans. That's important, because if we're removing water, it has implications for how much water was left. It appears that to develop a planet like Earth, you have to start out with a very robust inventory of water," Tarduno told Discovery News.
The planet's early shield was only 30 to 50 percent as powerful as the one that exists today, the research shows.
Extrapolating from studies of similar but younger sun-like stars, which produce more X-rays and high energy ultraviolet radiation than our middle-aged sun, scientists estimate that young Earth could deflect the solar wind only about half as far as it can today.
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