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Early Earth's chlorine blown away by giant impacts

Element has long puzzled scientists because modern levels are so low

Earthlings may owe a debt of gratitude to the enormous miniplanets that smashed into the planet in its youth. Such collisions might have knocked away much of the supply of chlorine concentrated on the planet’s surface, geochemists propose. Had that loss not occurred, the world’s oceans would have been too salty for complex life to thrive, they suggest.

The scenario may explain why Mars, which suffered fewer large impacts, may have more than twice as much chlorine as Earth does, the researchers report April 16 in Earth and Planetary Science Letters.

“The story seems to hang together pretty well,” says James Brenan, a geologist at the University of Toronto who wasn’t involved in the study. “Life, probably over a fairly long time, might have been able to adapt to this environment, though certainly things would be different than today.”

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