Dating rocks from the moon
Not all ages determined for anorthosites, however, are as old as we expected--one appeared to be only 4.29 billion years old.
While 4.29 billion years sounds very ancient, a magma ocean ought to have solidified well within 100 million years of lunar origin about 4.55 billion years ago.
These data fall on a well-defined line indicating a crystallization age for the anorthosites of 4.46 billion years, consistent with very early, widespread melting of the Moon. Chondritic meteorites have revealed an impressive portrait of conditions in the early nebula (see articles Dating the Earliest Solids in our Solar System and The First Rock in the Solar System), whereas igneous meteorites such as the eucrites provide a glimpse of what the early planets may have looked like (see article Asteroidal Lava Flows).
For example, the first studies of Moon rocks inspired John Wood (Smithsonian Astrophysical Observatory) to boldly imagine the idea that terrestrial planets must have been extensively molten soon after they formed.
This global melting event produced a stratified Moon with a low-density crust formed by accumulation of the mineral plagioclase overlying a higher density mantle of olivine and pyroxene.
Meteorite impacts have reworked the lunar crust extensively over the past 4.5 billion years, and most of the rocks returned from the Moon are breccias.
But even that age might have been affected by the subsequent shock heating event that reset the low-temperature components in this rock about 500 million years after it formed. (2003) Chronology, geochemistry, and petrology of a ferroan noritic anorthosite clast from Descartes breccia 67215: Clues to the age, origin, structure, and impact history of the lunar crust. 645-661.nderstanding the origins of planetary systems is one of the most central and challenging questions in planetary science.
By examining data for all of the previously dated lunar anorthosites, we were able to show that plagioclase feldspar is more prone to shock damage than are the pyroxenes in these rocks, so we plotted only the pyroxene data for four different anorthosites on a samarium-neodymium isochron diagram. The idea that the planets in our Solar System were assembled from a rotating disk of dust and gas known as the Solar Nebula is reasonably well established, but in detail we know surprisingly little about the actual events that lead to construction of the planets.