Hi Steve -

What is coming in from "historical" surveys for the last 5,000 years or so is that the Earth has been hit a large number of times by small impactors, called continent kilers and city killers, at a rate much higher than the numbers predicted by the earlier lunar crater counts.

We have two data sets, both poorly developed and currently at odds with each other, data sets with simply staggering implications: when the next one of these continent killers hits, we're looking at 3 to 4 times the total deaths in World War 2 occuring in an instant.

The historical impact rate for continent killers is turning out to be about 1 time per 1,000 years. And then of course a smaller city killer impact might set off a "nuclear exchange", as its sometimes refered too.

You're right in your hunch that you're missing something. The relationship between Mars impact rates and Earth impact rates is very complex and poorly explored. In part because this is because the maths are incredibly complex, in part because these models are poorly developed, and in large part simply because we simply lack the counts - we have some of the data, but it is unanalyzed.

Crater counts need to be exhautively compiled for all bodies in our solar system, and in addition to counts for Mars, counts need to be done on the Galileo imagery of Jupiter's moons. The Mars data is a real good place to start.

EP