The moon is older than previously thought, pushing back the clock for when conditions on Earth were suitable for life, research published on Wednesday shows.
A new analysis of zircon fragments trapped in rock samples retrieved by the Apollo 14 astronauts shows that the moon is 4.51 billion years old, meaning it formed within 60 million years of the birth of the solar system.
A previous study based on the same samples also showed the moon formed early, within 68 million years of the solar system's birth. Other estimates of the moon's age range from 100 million to 200 million years after the solar system's formation.
The discovery, published in this week's Science Advances, means Earth may have emerged from its battered youth years sooner than thought, setting an early stage for life.
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"If we believe that the moon was formed by one giant impact - or several smaller impacts during a short period, as proposed in the Nature Geoscience paper published on Monday - then whatever the proto-Earth looked like before was wiped out," University of California Los Angeles geologist Melanie Barboni wrote in an email to Seeker.
Today's Earth, with atmosphere, liquid surface water and other life-friendly conditions, only started to develop after the impact or impacts that formed the moon, so if that occurred late then life could only have developed late as well, she added.
"Our age places the impact(s) really early, which allow an hospitable Earth to develop much earlier as well," Barboni said.
The finding dovetails with related research showing early Earth was habitable earlier than previously thought, with the potential for life as far back as 4.1 billion years ago.
Having a moon-forming impact or impacts 4.3 billion years ago would leave relatively little time for life to evolve.
"At 4.51 billion years, you have much more time to transform the Earth from hellish to nice," Barboni said. "The age of the moon is indeed critical."
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To determine the moon's age, Barboni and colleagues used a new technique to examine eight zircon fragments left over from a previous study. Their uranium-lead dating method, used for the first time on lunar samples, corrects for cosmic ray exposure. The researchers also analyzed isotopes of the element hafnium, a silvery grey metal.
Like on Earth, the zircon fragments originated in magma rocks that were later weathered into sand and small pebbles. These were then incorporated into new rock.
"On the moon, the old rocks that contain zircons were pulverized by multiple impact and either transformed in sand (lunar soils) or incorporated into breccias (composed of bit and pieces of many rocks). Everything is mixed, probably from all over the moon. That's why whole rock is not usable to date the moon. The zircon on the other hand can," Barboni said.
"We are currently separating more zircons and will get more data soon. But I don't think it will change our age determination much - it would be more of a double-checking than anything else," she added.
Image: The Earth rises over the moon's landscape as seen by NASA's Lunar Reconnaissance Orbiter (NASA)
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