[meteorite-list] Look At All The Craters!

[Meteorites USA]

Thought this was interesting.

MARS
http://hirise-pds.lpl.arizona.edu/PDS/EXTRAS/RDR/ESP/ORB_014300_014399/ESP_014394_2045/ESP_014394_2045_RED.abrowse.jpg

When considering the number of craters visible on every planet in our 
solar system whose surface we can see, and which have hostile 
atmospheres, to zero atmosphere, and also taking into consideration 
terrestrial weathering, erosion, and other factors which erase traces of 
meteorite impact craters, why are there still so many craters visible on 
Mars?

When you look at the surfaces of the Moon, Mars, Venus, Mercury, the 
moons of the gas giants, and all asteroids especially Ceres, Vesta, Ida, 
and others, I would think you couldn't go very far on Earth without 
walking across or into the last remnants of a crater. I understand age 
and weathering and why there's no meteoritic material left around these 
most of the craters, but I guess my point is that given the sheer 
abundance of craters on every celestial body whose surface we can see 
would seem to me to be evidence of Earth's history as well.

Given that, is there technology or a mapping system that is capable of 
cataloging all of Earth's impact craters? I'm not talking about the 
really big ones we already know about, but the smaller hard to find 
craters in forests, under desert sands, and ocean floors. Evidence still 
exists of these craters... Would magnetic anomaly maps be helpful in 
finding craters? Lidar, or Radar? Has anyone ever attempted to map all 
the craters on Earth's surface minus the trees, oceans and man-made 
structures?

I know this is a lot of questions... ;)

Regards,
Eric Wichman
Meteorites USA