There is life on earth more than a mile below us all. You can sink a mine shaft down almost anywhere on the surface and find life deep underground. If we wanted to find life on Mars this is where we should be looking.
One this topic there is so much rock transfer between Mars and Earth (about 100kg a year) that both planets are effectively one ecosystem.
Here's an example. The structures inside the meteorite were't proved to be life but if they had been alive they would have survived the trip from Mars to Earth.
We have pulled living bacteria out of sediment 100 million years old so 17 million years is nothing. More importantly this is just the time for this particular meteorite - people have done the calculations and some meteorites do the trip in around a year.
That raises an interesting point. There are actually two different concepts of life on Mars:
1) Life that has a shared lineage with Earth life.
2) Life that is unrelated to Earth life.
#1 would be neat news, but it wouldn't be particularly earth shattering news (hah). As you mention, this would be through ejecta transfer - some primordial bacteria hitching a ride on interplanetary asteroid impact debris.
The thing about #1 is that we're almost certain it's completely plausible. We have extremophiles on Earth that live in conditions just as harsh as some of the places on Mars. The tricky part would be getting them there. Sadly, biological transfer between planets doesn't really help us fill in any of the variables in the Drake equation...
But #2 - that would be incredible. If we were to find life on Mars and we could prove that it had no relation to life on Earth, that forcibly changes everyone's cosmic perspective. Proving that life evolved independently twice in the same solar system would mean the universe must be teeming with it.
If I had to make a bet I would predict that we will find that there is life in a number of locations within the solar system (Mars, some of the moons of Jupiter and Saturn) and they will all be related to life on earth. The Earth has a cosmic cold and has been sneezing in all directions for billions of years.
One of the interesting things about bacteria is that there are two major lineages here on earth (the archea and the true bacteria). Some people have speculated that one arose on Earth and the other on Mars, but I doubt we will ever find good evidence for this speculation.
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[ 3.8 ms ] story [ 40.5 ms ] threadOne this topic there is so much rock transfer between Mars and Earth (about 100kg a year) that both planets are effectively one ecosystem.
http://en.wikipedia.org/wiki/Allan_Hills_84001
Here's a fun article about reviving supposedly 250 million year old spores trapped in salt crystals: http://www.its.caltech.edu/~bi1/Bi1__Micro-_to_Macro-Biology...
1. http://www.nap.edu/openbook.php?record_id=5563&page=17
The thing about #1 is that we're almost certain it's completely plausible. We have extremophiles on Earth that live in conditions just as harsh as some of the places on Mars. The tricky part would be getting them there. Sadly, biological transfer between planets doesn't really help us fill in any of the variables in the Drake equation...
But #2 - that would be incredible. If we were to find life on Mars and we could prove that it had no relation to life on Earth, that forcibly changes everyone's cosmic perspective. Proving that life evolved independently twice in the same solar system would mean the universe must be teeming with it.
[1] http://en.wikipedia.org/wiki/Tardigrade
One of the interesting things about bacteria is that there are two major lineages here on earth (the archea and the true bacteria). Some people have speculated that one arose on Earth and the other on Mars, but I doubt we will ever find good evidence for this speculation.