Oldest rocks on Earth

Andre

http://news.bbc.co.uk/1/hi/sci/tech/7639024.stm

It's not the oldest mineral though.

LURCH

If these rocks do indeed contain evidence of life from 4.2 8 billion years ago, would this not contradict current scientific models of how life occurred on the planet? It is my understanding that all the current models do not predict life arising until significantly later.

LURCH

Ooops! I geuss not; I just did a little quick research into current theories about the origins of life on Earth. The last time I checked, life was thought to have begun "about 3 billion years ago." Now I can see that I was taking a far too narrow view of the word "about." Current theories have life beginning anywhere between 2 1/2 to 4 1/2 billion years ago.

DEMcMillan

I found the question of how ancient was the origin of life most fascinating. If one divides life into prokaryotic and eukaryotic forms on the basis of the presence or absence of a nuclear membrane and distinctive chromosomes (mortality and sex), one immediately expects that earliest life should be the simpler prokaryote and its ring chromosome. Prokaryotic photosynthesis would be important to expand the organic carbon pool. Prokaryotic Archaea would use inorganic energy to change the Earth’s geology, but how they did they meet their own carbon needs? It seems that evidence of eukaryotic life more than 3 billion years ago is strong. But eukaryotes developed structures that could generate footprints only 570 million years ago. http://www.physicsforums.com/showthread.php?t=261925 Early evolution clearly moved slowly. Life’s influence on the planet over such a long period was strong but rather shadowy. How early did the chemical warfare between prokaryotes and eukaryotes start? How early can we find prokaryotic toxins and eukaryotic antibiotics?

Ophiolite

Methane, carbond dioxide, small organic molecules such as acetates and formates. I don't see any particular obstacle here. Do you feel these sources might somehow be unsuitable?I don't recall anything pointing to this since Hoyle made some claims along these lines in the 1970s. Since I am a proponent of panspermia I would love this evidence to be real, but I rather doubt it. Could you be more specific? (Or have I totally misunderstood your thesis? Are you suggesting that the only viable carbon source for the Archaea would be decomposing eukaryotes?)
Well, that is certainly correct for literal footprints, but not for metaphorical ones. Multicellular organisms are found in the late pre-Cambrian and traces of eukaryotes are found as early as 1500 my BP.

?This seems an odd tangent. What did you have in mind?

Andre

Welcome back, Ophiolite

billiards

I like panspermia too, but that can only explain how life gets started on a planet. How did it get started in the universe? How often does this happen? Could it be that it is continually happening on planets congenial to life, that it is happening under our very noses right now, but we cannot detect it, because it never is given the chance to evolve into a form that we would even recognize as being life?

Ophiolite

First let me summarise why I find panspermia appealing.
When we had little concept of the complexity of life, (when it was not all that long since Pasteur had shown that mice do not spontaeously emerge from dirty straw), it did not seem difficult to adopt Darwin's view and imagine a group of chemicals coming together by chance in some warm, little pond. Once we understood how complex even a 'simple' prokaryote is it became clear that there were many complex, inter-related steps necessary to move from life to non-life. The solution offered was that of time: complex as these steps were there was a lot of time for them to occur.

This has always seemed an unsatisfactory answer to me; a cop out; a fudge. Possibly that is all we need, a little time. Possibly the pathways to life are compelling and inevitable. (And that has teleological implications beyond the bounds of this discussion.) Possibly. But in the absence of any pathways that have been demonstrated, in detail, as being feasible and to which a time estimate can confidently be attached, we cannot say that life must have originated on Earth simply because it is here.

So how do we increase the odds of life developing somewhere? We need more time; we need organic chemicals in quantity; we need a substrate for them to adhere to and react on; we need as large a volume of these as possible, to increase the odds of something interesting happening; we need a temperature range in which water is liquid. (I'm going for the carbon based/water solvent view of life.)

Where can we find all those. Hot GMCs. The vast Giant Molecular Clouds that form the birth place of stars. All of them are loaded with organic molecules - well over one hundred types detected at the last count. Most of them are cold, but those which have begun to partially collapse, creating new stars, warm up as the stars switch on. That's my preferred location for the origin of life - intergalactic space.

(And for those planning to refute this 'nonsense' please don't try applying Occam's razor. It cuts both ways.)

DEMcMillan

I have been traveling. The reference for 3 billion years I kept was this
http://www.sciam.com/article.cfm?id=...ells&topicID=3 . It ends in an informed speculation. The http://en.wikipedia.org/wiki/Eukaryote gives 2.7 billion years based on shale steranes (2 refs). At least both are greater than 1.5 billion. Looking for specific agents beyond steranes could add to precision, so that I made the chemical warfare assertion. The size of the geological carbon pool generated my interest in Archaea carbon sources. Could an earlier prokaryote have had both photosynthesis and inorganic energy capabilities? A bigger DNA ring would be assumed, now shrunken. Otherwise, as with current Archaea, your model of volatile organics matches everything I know.

Your panspermia interest stirred memories of past speculation about the specificity of triplets in amino acid coding. It was felt that if life developed in different areas of the universe that the nucleic acid base triplet coding would vary because it seems so arbitrary. Would it be panspermia if life were limited to our planet?