In article ,
Arduin wrote:
Presumably some amount of ejecta from the earth made its way to the
moon, so would we be able to detect such materials from the earth?
That is, at presumably very low concentrations, would our current
technology allow us to determine the proportion of earth ejecta that
has made its way to the moon?

Unfortunately, no. Earth rocks and Moon rocks are not that different,
seen from a distance.

Folks have indeed suggested that you could find very old Earth rocks in
the lunar regolith... but the search would be difficult and tedious even
working on the lunar surface.

As a follow-on question, if some of this ejecta made its way to the
permanently shadowed south poles, would it be possible for rocks of
sufficient size to shield the contents in the center from the energy
of the ejection, the friction from the earth's atmosphere, and the
impact upon the lunar surface?

As demonstrated by the Mars meteorites, the energy of ejection is not a
big issue. (It used to be considered a prohibitive problem, but a closer
look says it's not so.) The lunar impact is a bigger question mark, but
apparently there is reason to suspect that at least occasionally part of a
rock would survive.

...But once at the south pole, the material
should end up deeply frozen, I would expect.

Maybe. It depends on the history of the Moon's axial tilt. Current
thought is that Earth's high gravity and thick atmosphere permit ejection
of intact rocks only from very large impacts, which were largely confined
to the very early days of the solar system. So such material would have
landed very early in the Moon's history.

Note also that there is considerable resurfacing of the Moon, even in the
polar regions, by smaller impacts. The polar hydrogen deposits are
thought to be frozen gas from comparatively recent comet impacts.
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MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
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