Tuesday, January 5, 2010
Rock of Ages
We were at dinner on the 31st December with a group of friends overlooking the horizon with the full moon rising. It is a "Blue Moon" my wife said. That got us talking about the moon and we got onto the subject of the lunar rocks brought back by the Apollo Missions and that lead the coversation to how to how old the moon was.
Well, the abundances of radioactive elements in rock samples can be used to tell the age of the rock in a process called Radioactive Dating. The lunar material was analysed and samples from Mare Imbrium and the Ocean of Storms brought back by Apollo 11 and Apollo 12 are about 3.5 billion years old, which is comparable to the oldest rocks found on the surface of the Earth.
What is interesting is that the ejecta blanket from the Imbrium Basin (which was formed by a gigantic meteor impact) was returned by Apollo 14 and found to be about 3.9 billion years old.
However, Lunar Highlands rocks returned by Apollo 16 are about 4 billion years old. The oldest lunar rock found was located by Apollo 17 and appears to be about 4.5 billion years old. So, the oldest material from the surface of the Moon is almost as old as we believe the Solar System to be. This is more than a billion years older than the oldest Earth rocks that have been found. Thus, the material brought back
from the Moon by the Apollo missions gives us a window on the very early history of our Solar System that would be difficult the find on the Earth, which is geologically active and has consequently, obliterated its early geological history.
The amount of cratering is usually an indication of the age of a geological feature. But more of this in a future blog.