Approximately 468 million years ago there were a large number of L-chondrite meteorites falling to Earth. This is called the Ordovician meteor event and was probably the result of a large collision in the asteroid belt.

Does the lunar cratering record also show evidence of this event?


1 Answer 1


The very, very short answer to your question is: "Not that's detectable by any current methods or data that we have."

The longer answer has to do with how we know how old anything is on the Moon or other planetary surfaces. What we do is we use craters themselves to date a surface: The more craters, the older the surface because it's been around longer to accumulate those craters. We can tie to those to an absolute age by saying that X rock sample collected by Apollo or Luna or Chang'e is Y years old (dated via radiometric methods) and it is from a surface that has Z craters. Do this a lot and you can build up a function that relates the number of craters to an age.

The problem comes in using this to date any specific craters to try to find a non-uniform function (e.g., an age spike): You have already assumed a crater chronology function that does NOT have that spike, so using it to find a spike becomes a circular argument that is very difficult to get out of. There are some proposals on how to do that, but they're based on models and not actual data (such as, the large objects that form large craters would show those spikes, but the small objects that form small craters are a steady "clock" of impacts).

Right now, the lunar crater chronology has roughly a dozen points on it, so we don't have the resolution to say anything about a spike ≈468 million years ago. It is certainly possible (likely, even) that the lunar crater record would show that spike if we had the resolution to measure it by dating many more craters through methods other than superposed crater measurements, and, indeed, it is generally assumed that the lunar crater chronology really should have lots of little spikes in it when asteroids break up / asteroid families form, but again we just don't have the data to really measure that ... yet.


You must log in to answer this question.