Man on the Moon Not So Old

Our moon may be 60 million years younger than we thought.

THE GIST

Analysis of lunar rocks collected by Apollo astronauts suggests the moon is about 4.36 billion years old.

That is about 60 million years younger than previous estimates.

The finding suggests that the oldest crusts on Earth and the moon formed at similar times.

A new study of lunar rocks collected by the Apollo 16 astronauts indicates the moon could be 60 million years younger than previously thought.

The work reported in the journal Nature places the moon's age at about 4.36 billion years.the

Lars Borg from the Lawrence Livermore National Laboratory in California and colleagues say their results suggest either the moon solidified far later than previous estimates or current assumptions about lunar crust formation from a global magma ocean are wrong.

Borg says the new younger age puts it closer to the 4.4 billion year age of the oldest known Earth minerals, zircons discovered at Jack Hills in Western Australia. It means the oldest crusts on both Earth and moon formed at similar times.

The prevailing hypothesis for the moon's origin, the giant impact theory, involves a collision between the early proto-Earth and another proto-planet called Theia, which was about the size of Mars. Melted ejecta and debris from this impact was thrown into space, eventually coalescing over millions of years to form the moon.

As the moon cooled, this magma solidified into different mineral components with lunar crustal rocks called ferroan anorthosites (FAN) being the oldest. But scientists have had difficulty dating FAN samples. .

Borg and colleagues used new refining techniques to analyze isotopes of lead and neodymium in their 1.88 gram sample of FAN from the lunar rock collection at NASA's Johnson Space Center. Their figure of 4.36 billion years pinpoints the time at which the sample crystallized. This figure is 200 million years after formation of the solar system and significantly later than assumed by most lunar formation models.

"It's the first time a single sample of FAN yielded consistent ages from multiple isotope dating techniques," Borg said. "Previous attempts to date these rocks have relied on just one isotopic clock which can be contaminated putting the age in error. So we started with the idea that we would get multiple age samples so we could have confidence it reflected the crystallization age of the sample."

Geologist Ian Graham from the University of New South Wales says the work is important not just in terms of dating the moon, but for geologic dating generally.

"A big problem with dating lead, uranium and similar minerals using an isotopic system is a thing called common lead which floats around and gets everywhere," said Graham. "If you have common lead contamination, it can be a very young age and give you erroneous dates. And so they've developed a technique to minimize common lead as much as possible giving you a very good precise age."

"The multiple washing and multiple partial dissolution in different acids, which removes the common lead is a real breakthrough. The paper also shows that we need to do more work on lunar materials," Graham siad.

"We are finding all these things out from samples collected years ago by the Apollo missions of the late 60s and early 70s."

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