Or, Maybe Edicarian biology was the "original" life on Earth until it was displaced by Martian lifeforms creating the Cambrian Explosion 542 Mya.

Earth has so many fabulous and varied ecosystems, harbouring every kind of life. We still have NO idea how life began but have proven that in almost any environment, the basic building blocks of life assemble almost automatically. (nice to hear for people who like a little company in the cosmos!) So as long as that first spark was here, and lord (small L) knows, we gots lots of sparks, then for absolutely sure, our earth would have made the most out of that possibility and encouraged the flourishing and abundance we see today. No need for extraterrestrial help, No need for meteorites and seeding. Life is here. Life did not start as an intelligent alien, but fossil records show that it started very modestly. That would indicate it started here, as a very basic model. That's why every bacteria is my buddy.

Why are these people refusing to accept the possibility that water, carbon and the other elements required for life existed on earth from its formation?

We could be Crabpeople as well, but it's another "could"

I think the planetary society are testing this theory out in an upcoming launch to Phobos.

As Alex was saying that this is not old news, sure that is correct and it just goes to show you that ALH84001 may indeed harbour fossilized proto-bacteria, all in all this is exciting stuff.

evidence … surviving a few years in space … three years prior … still living

All terms suggesting that the microbes had survived a few years in space and were still living when the camera was inspected. I'm sorry you've had so much trouble with those two paragraphs, and I hope this helps.

why is it always Mars?
We couldn't have come from somewhere else?
Somewhere deeper in space.."

I agree. Why not Martian microbes coming from Terrestrial or Venusian origins. Venus was warmer and likely had global oceans; add in a huge volcano from Aphrodite Terra and "ka-pow" life springs into existence on Venus…. not that I'm actually seriously suggesting this scenario.

I suspect that Terrestrial life popped into existence right here on Terra Firma (Terra Aqua?) and has been multiplying and mutating away for æons.

According to percisely who us this common knowledge?
And How do you know that this common knowledge is actually true?

You tell me how I am to interepret this:

Surveyor 3, an unmanned lander that had touched down nearly three years prior. Earthly microbes – including those associated with the common cold — were still living inside the camera box.

“The records were good enough to show one of the technicians had a cold when he was working on it,” he [Melosh] said.

Biological exchange between not only planets but between various past and present star systems is very much probable.

The extent of development of life probably depends upon the environment that the genetic code finds itself in. By this logic Earth is the most likely candidate in the solar system to have captured and propagated this code rather than receiving it through other planets in the solar system.

However, this guess is on the basis of what we are seeing today. Perhaps the conditions might have been more conducive on Mars and even on Venus compared to Earth in the distant past. It is probable that life might have taken a root in these places and then found a better environment to thrive on Earth.

It is less probable to imagine that life originated from scratch on Mars and then came to Earth.

In the future when a catastrophe strikes planet Earth it is possible that a good chunk of bacterial life with the genetic code shall be ejected out into interplanetary or even interstellar space. The bigger the impact the more distance it will travel taking the genetic code to safety. For a small impact some of these chunks of rock will fall back to the Earth itself bringing back the seeds of life to flourish again after the bad times are over. When the impact is so big that the life cannot flourish again, the rocks would have momentum to leave the solar system and try to hunt another place to settle!

But science isn't about possibility.

Imagination is about possibility; science is about what is.

It's also possible that Venus was a comet Phaeton that disturbed the orbits of the solar system and caused a catastrophic meteor shower, conflagration, and deluge but saying so causes fundamentalists to start drooling and frothing at the mouth.

Mars should once have been a fertile place for genetic material, if the rare events of ejection with escape velocity might have transported "sources of infection" not only into interplanetary space, but also to a tiny spot named Earth, injecting Earth with fertile instead of futile rocky bio-carriers.

Therefore, if the panspermia theory holds true, we should on the other hand also detect frutile material from earth in every corner of this solar system.

"Our" microbes should also be "outdoors", if the theory of life from Mars holds true!

It's a good idea for comic books but in reality it's a little far fetched. On the other hand, if they do find microbes on Mars, what is the bet they came from Earth? The impact thing works both ways right ? You could have microbes coming from Earth and raining into Mars. This event is far more probable than the Mars seeding Earth event.