[Matthew Lewis]

Matthew Lewis  asked the Naked Scientists:







   







Dear the Naked scientists,















I saw on TV (so i tmust be true) that up to 10% of the matter ejected by the Chicxulub Meteorite impact achieved escape velocity and was ejected into space. http://en.wikipedia.org/wiki/Chicxulub_crater















If the impact left detectable traces in the KT boundary, even if most of that is deposits from indirect effects, my question is:















Is there an analouge of the KT boundary on Earth, found on the moon made from ejected impact matter captured by the moon's gravity?















Cheers,















Matt Lewis (UK).















P.S.















Great show! Love it!















What do you think?

[graham.d]

Hi Matthew. This is not my field but I will have a go at answering as nobody else has yet. The K-T boundary defines the distinct change between the Cretaceous and Tertiary periods around 65 million years ago. These are notable changes to the earth that are reflected by the type of species of plants and animals and are characterised by apparant mass extinctions, most notably of dinosaurs, over a very short period of time.

The discovery of a high concentration of Iridium associated with the K-T boundary supports the theory of the cause of the extinctions was one or more massive meterorite strikes (meteors tend to have a high Iridium content).

To answer your question, it may be difficult to find any such analogue to the K-T boundary on the moon as a result of a correlated meteorite impact because there would be no specific dramatic change on the moon to mark such an event. The moon is full of craters formed since its solidification around 3.5 billion years ago. It is also subject to many smaller impacts from which the earth is shielded by its atmoshere. The best way to find something that may correlate with the K-T period would be if the ejected material (assuming the TV programme you saw was correct) comprised material peculiar to the earth at that time which were effectively then deposited on the moon. I think if 10% of material was ejected into space then it is quite likely that some of this would be captured by the moon.

Note though that it is not sufficient to just achieve escape velocity to get ejected into space because this neglects the considerable effect of atmospheric friction. The velocity of any ejected material would have to be considerably higher and there would be some filtering effects of what size/mass of objects would make it out. Small pieces would not get out, I suspect, because their surface area to mass ratio would be too high and air friction would dominate. Very large objects may not be structurally strong enough to remain in one piece, given the huge forces involved during impact as well as the thermal stresses that would be created. It would be interesting to have a second opinion on the TV programme's assertions although it is widely accepted that some stuff we find on earth may have originated on Mars and got here by similar means, so it seems plausible that their 10% number is right.