Earthed

How do meteorites originate from planets?

Scientists have found a number of meteorites that they claim have originated from other planets such as Mars. One even had what appeared to be microscopic fossilized bacteria. How do meteorites get off planets, and how would fossilized bacteria survive the process?
It just seems strange to me that scientists could assume tiny microscopic fossils could withstand the initial impact, as well as the descent through the Earth's atmosphere, doesnt it?

Public Comments

1. On impact from meteors or asteroids, material
   
   from planets will be launched into space.
   
   Tektites which can be found in rock shops and
   
   meteorite dealer's websites are believed to
   
   be meteorites originating from the earth. Similar
   
   to obsidian glass, they traveled through space,
   
   but not from a great distance. It is likely an
   
   asteroid impacted in South America and the
   
   debris actually reached space.
2. Most of the 10's of thousands of meteroites that we have found are from asteroids, but there are a few that we have identified as being from the Moon and from Mars (about 20-30 of each). The way you knock a chunck of rock off of another world is to have a meteorite strike that world at a very shallow angle. You can then "chip-off" a rock at a high enough velocity that it can escpape the planet and drift trhough the solar system. Earth does a pretty good job of sweeping up moon debris, and anything randomly launched from mars has about a 9% chance of winding up on earth.
   
   
   
   If fosils exist in these rocks then they will be brought to earth as well, just like any other rock (after all fosils are rocks, just _very_ inetersting ones).
   
   
   
   The Martian meteorite that caused a stir with "life" a while back was ALH84001. It has been since shown that the evidence for life was more than likely either a natural process, or a result of the rock sitting in Antarctica for a very long time. No bacteria was ever claimed for this rock, but some researchers felt that some of the mineral formations were indicative of life. Since these formations can be explained through natural (non-living) processes, most scientists have dismissed it as evidence for life. But who knows, maybe the next martian meteorite we find will have stronger evidence it in.
   
   
   
   Comment on Tektites: They are terrestrial in origin. They are formed out of earth material melted and thrown into the air by impacts, but are made out of material from the impact site, rather than the impactor.