A Huge Slice of the Moon

The largest known Moon Rock on Earth from the ancient Lunar Highlands, NWA5000 was much larger than any brought back by Apollo. It was ejected from the moon by an asteroid strike ~2000 years ago, and after hurtling through space and around the sun for over 1.3 thousand years, landed in the Western Sahara desert to be discovered in 2007.

Only 0.1% of meteorites are from the moon, making them more rare than pure diamond on Earth. With this unique slice of heaven at work now, I am, needless to say, over the moon!

I just noticed that it was this particular slice that went through the meteoritical analysis at the University of Washington.

From the site dedicated to this meteorite

The matrix looks like a black and white intaglio print of the universe rendered by a spirited yet masterful artist. This stone contains breccias within breccias, and the preferential orientation of clasts (from impact compression) lends a unique 3D appearance to flat surfaces. A generous amount of 4.5-billion year old gleaming metal is present, adding yet another striking element to nature’s artwork.

We know from remote observation and the Luna/Apollo missions that there are two main classes of rocks from the Moon. The first type is referred to as “mare” (meaning “sea”), pertaining to the darker areas of the Moon mainly composed of ancient (3.0 to 3.8 billion year old) basalt lava flows. The second type referred to as “highlands” pertains to the lighter colored areas of the Moon mainly composed of feldspar-rich anorthosite rocks. NWA 5000 is a unique highlands- monomict gabbroic breccia (meaning a type of rock mainly made of related fragments of gabbro). The Moon is believed to be about 4.5 billion years old and for about 600 million years during its early history was bombarded by pieces left over from formation of the planets. Impactors continued to strike the Moon at a decreasing rate, creating the heavily cratered surface of the lunar crust. During this time, melting of the deeper lunar mantle produced fluid basalt magma that erupted into the larger impact basins producing the dark areas of the the lunar surface (“maria”). Knowing this history of the Moon, we can infer that NWA 5000 is very ancient, and much older than most known Earth rocks.

The next period of NWA 5000’s existence was relatively quiet until a massive impact event occurring around 3.2 billion years ago created a giant melt sheet of a type of rock referred to as gabbro. The impacting body left exotic material in this Lunaite, solving the mystery of why there is metal embedded in the gabbro clasts, (something that was never observed before NWA 5000 was studied.) Another asteroid impact around 600 million years ago was mostly responsible for producing its distinctive brecciated matrix as well as bringing this rock to the surface of the Moon. This is where it was exposed to the solar wind, which implanted hydrogen-rich gas bubbles into the matrix. Then another impact event ejected this rock from the Moon and created the cross-cutting, thin glass veins. According to ongoing studies, this happened around two thousand years ago.