Where did we come from?

I think we don't have a clue how life got started. Just a lot of not very well tested theories and new ones appear all the time. So it's jumping the gun to say water was absolutely the key to it all.

As for liquid water, some bacteria have been proven to produce antifreeze which melts the frozen water around them for their use in their micrometre sized bubbles. http://news.sciencemag.org/sciencenow/2010/04/frostbite-not-for-these-microbes.html

Bacteria's metabolism (meaning the chemical reactions they depend on to create energy and therefore the things they can live on) is incredibly diverse, probably much more than multi-cellular organisms and this points to the lie of thinking of them as 'simple' life-forms. they are not simple, they just have less genes and DNA than most multi-cellular organisms. However randomly DNA sequence a 100 different bacterial species and you will see a huge diversity of genes and metabolic pathways. Some bacteria live in complex communities and evolve as part of the ecosystem and the community they live in. I just think we know so little about bacteria on earth and seem pretty blind to that sometimes. Finally there could indeed be other life forms in our environment but we haven't detected them yet. Unlikely but still possible,especially in environments we are not very familiar with like upper athmosphere, deep earth. Remember most bacteria on Earth cannot be grown in a lab, we only know they exist from a technique which can detect their RNA.

As for the fact that all life on earth seems to have a common progenitor it's certainly very interesting. But it doesn't mean that life could have formed by other methods..perhaps our current DNA based life (most theories even say DNA was not the precursor molecule of life) took over the niches that these other organisms may have occupied if they had a chance...or outcompeted them...or it really was a fluke and life only popped up once (statistically doesn't make sense, if it appears once it should appear more often, especially as life seems to have formed as soon as the crust solidified on early Earth). So I favour the theory that current lifeforms simply outcompeted other forms when they popped up. There are some major divisions early on though - archaea and bacteria. Although my favourite theory is that life was indeed seeded from outside. That might make the most sense given the size of the galaxy and the universe.

http://www.panspermia.org/bacteria.htm

Doing a little thought experiment, zoom out your view of Earth so that is one of only billions of planets in billions of solar systems in the Milky Way alone. Does it make sense to think of it as an 'isolated' earth or as part of a bigger ecosystem which is exchanging comets and dust and where solar systems pass each other as they whirl around the milky way. Wouldn't the idea of Earth being isolated start to look as ridiculous as a tree in the middle of a forest being isolated? I think the reason people feel Earth and the solar system is lonely is that the distance seems huge on our human terms, mainly because of our lifespans and limited technology at present. But it is not huge in the terms of the universe's history (12 billion years and counting).

I think it's a huge mistake to limit the search for life just to 'our type of life' on earth. That just doesn't make sense as life is a series of self-sustaining chemical reactions and chemical reactions would be different in different environments.

Genghiz Cohen wrote: »

Kick back and enjoy:

This is a good theory, it's plausible..but it may not be correct.

Okay, as far as I know it.

Theory 1:
There was water on Mars, This is shown because there is evaporated salt on the ground & the salt is supposed to have formed on mars in the prescence
of water. Basically asteroids struck Mars & knocked some of the surface rocks into space & these collided with earth.
There are plenty of Martian rocks that have been found on earth to give credence to this hypothesis. Martian bacteria on the rocks that originated in the once-present Martian seas could have been taken along for the ride... Furthermore, extremophile bacteria would be more than capable of surviving on those rocks in space for X number of years.

Theory 2:
The same situation with Venus only there is a lot less evidence for this one. Venus could have had hospitable life before what is called the "runaway greenhouse effect" that has taken over Venus' surface.

Theory 3:
The Szostak abiogenesis video that has just been posted.
That is my personal favourite as it seems so plausible but I haven't really read any counter-criticism of it , which I'm sure exists.

Theory 4:
The Miller-Urey experiment extrapolated to the max!

Theory 5:
God did it in 6 days...

All I can think of for now :pac:

gbee wrote: »

we could easily be on our third planet by now, but still kept in the dark

I often thought that myself, if we want our species to survive, we really need to learn how to planet hop

If we set up a colony on the moon, I vote for naming them
Lunatics

<pedantry>

We didn't evolve from apes, we do, however, share a common ancestor

</pedantry>

snuggles285 wrote: »

what common ancestor is that?

Not found yet, normally referred to as the 'missing link'

What if we're all dolls being operated by something/someone or a monkey?

I imagine it's something scientific, a cross between evolution and pure chance to be honest