QUESTION:
I wanted to know why it is that we have found rocks from Mars on earth but we
have not heard of many rocks coming from the moon which is much closer and
more likely to have rocks knocked to earth due to its low gravity and lack of
atmosphere. It seems to me that the chances of rocks coming from Mars would
be remote due to it position and the escape velocity needed for a rock to
leave the Mars Atmosphere and then travel to the Earth. 

ANSWER from Geoff Briggs on January 30, 1997:
There are in fact many Antarctic meteorites that come from the Moon -- many
more than from Mars (for the reason you give).  But, because of the huge
sample gathering carried out by the Apollo astronauts in the 1970's,  they
haven't added to our knowledge as much as the Mars rock has -- so they have
not been given media attention.

ANSWER from Jeff Plescia on January 31, 1997:
Regarding your first question - we have found rocks from the Moon as
meteorites on the Earth. Virtaully all have been found in Antartica.
When people began to look at the chemistry of some of the meteorites
they realized they were very different from the other ones and
identical to the lunar rocks. That's how they were determined to
have come from the Moon (They are also very different from Earth
rocks). We don't know where on the Moon they come from.

Regarding Mars rocks, most of these too have been found in Antartica.
People originally did not believe it would be possible to launch
a rock off Mars and have it make it to the Earth. But the discovery
of the lunar meteorites and the recognition that some of the
meteorites were from Mars forced them to look at the problem again.
It is difficult since you must launch the rock at many kilometers
per second speed from Mars and then it must survive entry into the
Earth's atmosphere. There's probably a lot of lunar and martian rocks
floating in space and many more that burned up in the atmosphere.