Most of the things have been answered by CC already, but maybe i can add one or two aspects.
@TG:
Life is often portrayed as arising from some sort of “primordial soup”. There it is nutrients in a primitive sea, a lightning strike in the distance is imparting the energy of life. But to go from a barren lifeless planet to a one filled with living things, we would have to pass through a number of stages:
- EARLY ATMOSPHERE -
For starters we need a favorable environment for life to evolve and be sustained.
It looks like that has been the case, see below.
- SIMPLE ORGANIC MOLECULES -
We need a means of constructing the building blocks of life.
done in the lab, see below
- LARGE MACRO-MOLECULES (proteins, DNA, RNA, etc.) -
Some the simple molecules must be assembled into biologically useful large molecules.
done in the lab, see below
- BIOLOGICAL SYSTEMS -
Biological systems such as energy conversion must be constructed.
there are hypothesis’s for that, see below
- LIVING CELL -
And finally, all these molecules and systems must be assembled together to form a highly complex living cell.
there are hypothesis for that, see below
Now starting from the beginning, our current atmosphere consists primarily of oxygen (21%) and nitrogen (78%) and is called oxidizing because of chemical reactions produced by oxygen. The presence of oxygen in a hypothetical primordial atmosphere poses a difficult problem for notions of self-assembling molecules. If oxygen were present, there would be no amino acids, sugars, purines, etc. Amino acids and sugars react with oxygen to form carbon dioxide (CO2) and water.
Because it is impossible for life to evolve with oxygen, evolutionists theorize an early atmosphere without oxygen. Instead, they propose an atmosphere, which contains free hydrogen. Originally, they postulated an atmosphere consisting of carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), ammonia (NH3), free hydrogen and water vapor.
There is a problem if you consider the ozone (O3) layer, which protects the earth from ultraviolet rays. Without this layer, organic molecules would be broken down and life would soon be eliminated. But if you have oxygen, it prevents life from starting.
Unless you “form” the molecules in a different regime from where they later exist. Assume a large, deep mass of water. It will absorb the UV, so its deeper layers are UV-free. Forming can happening close to the atmosphere, and those molecules that drop to deeper sealevels will not be destroyed (see Urey effect for that).
And of course: the ozone layer is very (!) far away from where the action takes place. But from what i read, it wasn’t there, my sources assume a reducing atmosphere.
In must be noted at this point that the existence of a reducing atmosphere is theoretical and does not rely on physical evidence. To the contrary, there are geological evidences for the existence of an oxidizing atmosphere as far back as can be determined. Among these are: the precipitation of limestone (calcium carbonate) in great quantities, the oxidation of ferrous iron in early rocks and the distribution of minerals in early sedimentary rocks.
There then seem to be at least two different points of view. I guess for each reference to the oxydating atmosphere i can give one which proofs the reducing atmosphere.
This question therefor is open, and cannot be used to disproof something.
“Then i will look around for a source of the lab experiment, where they did just that, creating a reproducing molecule in conditions that once were predominant on our earth (AFAWK).”
Honestly, I would like to see this. Can there really be life from dead chemicals?
Ok, i looked around:
in 1953 there was an expermiment by Stanley Miller in Chicageo, who showed that you can build biological molecules out of non-biological ones. (he used an atmosphere of Hydrogen, Methan, Ammonia and watere electrical discharges, and could show that aminoacids, carbonhydrates and lipo-acids were produced. There was no ammonia in the early atmosphere as far as we know today, but he showed that you can build the needed molecules to start life out of others.)
Later similar experiments (don’t know who) showed that you can build purines and pyrimidine (which are part of the RNA!) out of the primordial soup
The very first catalyser for the forming of self reproducing molecules could be a crystal called Pyrit, which is (after the webpage i found, don’t know much about cryzstals) an electrically self-polarizing crystal, means it provides an electric field at its ends. Martin Keller from Regensburg showed that this crystal enhances biochemical reactions.
Scientists from the Rensselaer Polytechnic Institute (State NY), showed that another crystal could have worked as some kind of “skeleton” for the formation of RNA.
So, the first “life” without a “cell” could have taken place in and under the protection of these crystalline “reactors” (also calcit could be important, but i didn’t find more than just it being mentioned).
There seems to be one cylce (citronic acid cycle would be the literal translation) that still takes place in archaebacteria, which synthesis organic carbon out of CO2, and produces peptides and lipids as secondary products (which you need to build the cell membrane).
“Nuitrition” for the first organism can be supplied by the underwater “black smokers” who supply hydrogen and ironsulfid.
Another hypothesis:
It has been showed that dust coulds in space contain sugars and proteins. NASA scientists set up an experiment, forming “comets”, that is iceblocks at near absolute zero, out of water, methan, ammonia, CO and CO2, fomred it under conditions of temperature, darkness and vaccum that you would find in space ( you will find the same chemical components as well). UV Radiation then lead to the forming of many and some very large molecules. Bringing these molecules into contact with water, they spontanously formed protocells (which means, some of the molecules must have been lipo-acids), that is a cell-membrane with nothing in it. Still, creating a membrane “out of nothing” can happen! See some article in the „Proceedings of the National Academy of Science“ for that.
In short: if you are interested, google for it :). looking for “molecules” and “primordial soup” gives some hits. “Miller” and “Urey” can help as well.
