Friday, June 13, 2014

Earth-Moon Smashup Happened Earlier Than Thought

Earth-Moon Smashup Happened Earlier Than Thought
The moon was likely born after a Mars-size body slammed into Earth

Earth's moon sprung to life much sooner than scientists thought, new research suggests.
Previously, scientists had pinned down the moon's birth at 100 million years after the solar system formed 4.568 billion years ago. New findings push back the moon's birth date to just 40 million years after the solar system coalesced, researchers said yesterday (June 10) here at the annual Goldschmidt geochemistry conference.
The leading theory for how the moon was born suggests it originated from a Mars-size body slamming into Earth. Though the collision was only a glancing blow, the giant impact destroyed the impacting planet, called Theia. The resulting debris became the moon, though Earth also contributed some rubble. [The 5 Biggest Mysteries of Earth's Moon]
To calculate when this giant impact took place, geochemists Guillaume Avice and Bernard Marty analyzed xenon gas trapped in tiny bubbles in ancient quartz from South Africa and Australia. The quartz bubbles from South Africa and Australia retain the chemical signature of Earth's atmosphere from when the bubbles formed, like a time capsule from 3.4 billion and 2.7 billion years, respectively.
The amount of xenon isotopes (atoms with different numbers of neutrons) in the quartz is different than it is today. There's more xenon in the older rocks, because the noble gas has slowly escaped into space since the Earth's atmosphere formed. 
By measuring how much xenon is in today's atmosphere and comparing it to past levels in the ancient rocks, Avice and Marty gauged how much gas was present in Earth's earliest atmosphere. Their model assumes that all of Earth's gases (also called volatiles) were blown away by the impact. 
And the only event powerful enough to remove Earth's atmosphere was a planetary impact, the researchers said. The early solar system was a violent place, and models suggest the young Earth underwent up to a dozen massive blows from other planet-size objects — which helped Earth boost its size — before the final smash that spawned the moon. Later impacts were too small to strip the atmosphere, Avice said.
If some of Earth's atmosphere remained after the Earth-Theia impact, as some models suggest, then the new xenon age would shift toward a date of 100 million years after the solar system formed, instead of the younger age of 40 million years after the formation of the solar system, Avice told Live Science.
article taken from Yahoo! (original link)



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