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Sunday, August 28, 2011

The moon may be younger than we thought

The moon may not be 4.57 billion years old as previously thought.  It may actually be only 4.36 billion years old.  Does this make any difference?  It could mean that the moon was not formed the way we thought it was.

The prevailing theory is that the  moon was created from the aftermath of a collision between a Mars-sized object and the early Earth.  That part of the theory is not in question.  It's what happened next that may need to be revisited.
Currently, most astronomers believe that the collision caused the ejection from the Earth’s surface of an ocean of magma.  This molten material found itself in orbit around the Earth where it slowly solidified from the inside out. 

As the moon cooled, the lighter rocks floated to the surface and became the oldest rocks in the moon’s crust.  One such rock, ferroan anorthosite (FAN) was brought back by the Apollo astronauts. Previous attempts to date the FAN samples have been inconsistent, but new techniques used by Lars Borg of Lawrence Livermore National Laboratory and his colleagues from the University of Copenhagen, Carnegie Institution and Clermont Universit√© have yielded uniform results.  The oldest lunar rocks are about 210 million years younger than previously thought.

Although a difference of less than 5% may not seem like a big deal, it means that the moon’s surface did not form at the time we thought it did.  Either the moon solidified later, in which case the entire moon is younger than we thought, or the moon’s crust was not the product of a cooling magma ocean.