Were We the First on Planet Earth?

[skywalker]

Are we native to this planet The reason I ask is because of Man's inherent fascination with the starts.

Do we want to go back there Yes we are made of "Star Stuff".... that is what Carl Sagan said many years ago I'm a layman at such things technical as to how this planet was seeded,yes that is how I look at it this planet to me was seeded.

Whether by asteroids or comets or something else... And if this planet is the norm as far as this type of planet goes wouldn't we develop the same no matter where this type of planet is at Because the same forces that formed this planet would be the same elsewhere given a like planet and Star system existed The Cosmos is a very large place......

[rocket]

It's possible that life was seeded here from either a comet, asteroid, etc. Don't think we'll ever know the answer to that one. But I seriously doubt that even if it was, we won't find species like ourselves on the "mother world". Evolution of species really depends on the environment. Even if the home world was Earth-like, it probably won't be EXACTLY like Earth. Also, you have periodic cataclysms (asteroids/comets hitting, volcanos, etc) that cause mass extinctions. What species live and which ones die seems like a bit of a crapshoot.

The species will probably be very similar in a lot of ways (assuming the mother world is Earth-like). Factors like high oxygen level, gravity, relative abundances of various minerals/ chemicals etc will be the same, so the species that will flourish on both worlds will be the ones that can best adapt to these specs... but will there be "humans" that have developed just like us, with our (so called) intelligence I doubt it...there are just too many variables throughout the last 4 billion years of life on Earth for that to happen.

My 2 cents,

[Falcon]

"Panspermia" is the theory that life started somewhere (else), then got blasted all over the solar system.

The DNA code and all the intertwined biological pathways are pretty complex. I find it hard to believe that all that code and all the biological pathways could be completely reproduced exactly the same from scratch. I would bet that any "alien" life would be recognizably alien if it had a totally different genesis.

Parallel evolution does not mean totally convergent evolution. The classic example is the eye of the octopus: same basic function as ours, same overall strategy as ours (gather light and focus to nerves), but the devil is in the details. An octopus eye is constructed very different to a vertebrate eye. (Another example is a trilobite eye: very high performance, but again, a totally different design from either the vertebrate or octopus eye.)

So if we ever find life on Mars/Titan/Europa and discover it has DNA-->mRNA-->protein translation/transcription system and a Kreb's Citric acid cycle (for instance) we might eventually find it shares a chunk of DNA gene code with Earth-based life. That would provide evidence supporting Panspermia.

If however, we find Europan life doesn't use DNA, or has a really whacky metabolic cycle (where we couldn't imagine an adaptation from Terran pathways to Europan), that would provide evidence supporting that life started at least twice.

It is even possible that life started on Earth multiple times, but that only one type eventually flourished. Either through competition or just plain luck. Life may have been wiped out completely on the planet multiple times. (And may have been reseeded from other worlds.)

Lotsa possibilites, and I look forward to the day that we get a biochemical glimpse of life from another planet.