zachsdad:
I haven't heard about the possible impact yet. Is there a source to check that out? The chances of any martian impact generating enough force to effect Earth are negligable. However, it is possible for debris ejected into space by the impact to reach the Earth as meteorites. There have been a number of metorites found that are martian in origin. I have no clue as to how long it would take for that debris to reach the Earth. My best guess is that it could take a very, very long time, perhaps thousands or even millions of years before Earth's orbit would cross the expanding martian debris field. That is just a guess. There are other members of the forums who are much better qualified to answer than I.
Orbital simulations show times of from one million years to a few dozen million years for a soft-ball-sized rock to travel from Mars to Earth orbit after being blasted off the Martian surface by an impact. You start with the mass/velocity parameters given the escape velocity from the Martian surface and the size and velocity of the impactor, factor in not only the distance but also the orbital resonances likely to be encountered enroute, then end up with a very wide error bar due to the guesstimations required.
On the other hand, meteoriticists measure cosmic-ray tracks in crystals in meteorites whose vaporization spectra match that of gases measured by Viking spacecraft experiments. These tracks can give the amount of time the meteorite was exposed to the vacuum of space (atmospheres even as thin as those of Mars can block most of the cosmic ray bombardment, so the theory is that the number of -- and penetration level of -- cosmic ray tracks is an indicator of the time the rock spent "in space"). This is called the exposure age. For calibration, they use cosmic ray track counts from quartz crystals in surface rocks brought back from the Moon by Apollo astronauts. (Incidentally, this is a "smoking gun" proof that the rocks are not of terrestrial origin.) When you take the exposure ages of the handful of "known" Martian meteorites, you get transit time estimates of from 3 million to 12 million years.
About 10 meteorites have been positively confirmed as having the same gas concentrations as those in the Viking samples. All but one of these are of the same petrological (rock) type, so it is often assumed that any meteorite of that rock type is also a Martian sample (which is how so many "Rocks from Mars!" end up on eBay, for example). There are something like four dozen meteorites that meteoriticists identify as Martian with any confidence.