Abiogenesis

[otseng]

What was the first life form on earth? How did it come about?

[Iconoclast]

The first form of organic material was an amino acid, not unlike semen.

[Illyricum]

And where did the amino acid come from?

[Mightor]

And where did the amino acid come from?

Mightor say many amino acids occur naturally. Mightor say even find organic compounds on comets and asteroids. Halley's Comet may be 25% organic.

[Yahweh]

I"ll sum up Abiogenesis in a nutshell:

Abiogenesis (simplified) looks like this:
Simple Chemicals

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Polymers

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Replicating Polymers

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Hypercycle

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Protobiont

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Simple Cells


Quite a bit of research has gone into abiogenesis, here is lots and lots of useful information:

Synthesis of complex molecules in space. (Kuzicheva EA & Gontareva NB,1999. The possibility of nucleotide abiogenetic synthesis in conditions of 'KOSMOS-2044' satellite space flight. Advances in Space Research 23(2): 393-396.)( Schueller,Gretel, 1998 (12 Sep.). Stuff of Life. New Scientist, http://www.newscientist.com/hottopics/a ... tuffof.jsp)

Research into molecule formation in different atmospheres. (http://talkorigins.org/indexcc/CB/CB035.html)

Synthesis of constituents in the "iron-sulfur" world around hydrothermal vents. (Cody, GD et al.,2000. Primordial carbonylated iron-sulfur compounds and the synthesis of pyruvate. Science 289:1337-1340.)( Russell, M.J. and Hall, A.J., 1997. Theemergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and pH front. Journal of the Geological Society of London154: 377-402.)( Russell M.J., Hall A.J., Daia D, Turner D. and Rahman L.,1997. The emergence of life from iron sulphide compartments at a submarine hydrothermal redox and pHfront. http://www.gla.ac.uk/projects/originofl ... &_Hall.pdf)

And where did the amino acid come from?

(A copy and paste from here)

Living things as we know them are made of organic materials. In many instances, the organic materials are organized as chains of amino acids to form proteins. Proteins are "the building blocks of life," and amino acids are "the building blocks of proteins."

In a series of famous experiments by Miller and Urey (and others), organic materials (water, ammonia, hydrogen and methane) were put into a container and were subjected to electrical arcs (to simulate lightning). In a very short time (less than a week), amino acids and other organic compounds appeared in the container. There was no human creator, no designer... these things just formed under ordinary conditions.

If the same forces are at work for billions of years, the formation of life becomes probable. Not just possible, but highly probable.

The Miller-Urey experiments have been repeated under a number of different conditions and with many other experts in the field of biology (Stribling, Schlesinger, Chang, etc), the simple amino acids will form under a wide variety of conditions all on their own (and without risk of being destroyed by the very atmosphere they are within). No intelligent designer necessary.

[Didymus]

Note that there is a big difference in this question between the first replicator and the first lifeform.

THis is simply because biology uses a definition of 'life' that is much older that evolution is. You probably all know that one I'm talking about. Respiration, reproduciton, response to stimulus, some form of motion etc. Basically, anything that is itself a cell, or is composed of them. This definition is as old as the hills, and it was invented as so many biological definitions are (see my recent post in the 'identifying species' thread), for the convenience of biologists when identifying organisms.

It's most definitely NOT thought that the entity that abiogenesis research is the primary focus of was a cell. Instead, it's the first replicator. The criteria for that is much more simple; it must copy itself, it must be mutable (the copies are capable of differing slightly from the parent), and there must be heritability, meaning that those differences can be passed from the 'parent' to the 'offspring' (scare quotes, because I'm using terms that should only refer to true organisms, and we're exploring one of the biggest grey areas in existance).

The most fashionable candidate for first replicator seems to currently be an amino acid polymer of some kind, but there are still a good many who still have their money on RNA molecules.

So, there's a big difference between the first traditionally defined 'life' form, and the first replicator which would be capable of evolving into a lifeform, i.e. a cell. This is because 'life' is not as clear cut as human minds would like it to be. The distinction between life and non life is, contrary to popular assumtion, not clear but subjective and largely arbitrary.

[otseng]

So, there's a big difference between the first traditionally defined 'life' form, and the first replicator which would be capable of evolving into a lifeform, i.e. a cell. This is because 'life' is not as clear cut as human minds would like it to be. The distinction between life and non life is, contrary to popular assumtion, not clear but subjective and largely arbitrary.

Assuming common descent to be true, then my definition for the first life form would be the life form form which all life is ultimately derived from. Would this be a fair description of the first life form? If so, what is it and how did it come about?

I"ll sum up Abiogenesis in a nutshell:

Abiogenesis (simplified) looks like this:
Simple Chemicals

|
\/

Polymers

|
\/

Replicating Polymers

|
\/

Hypercycle

|
\/

Protobiont

|
\/

Simple Cells

In the same way, I can say that's how a computer is made:

Sand -> Silicon -> Silicon wafer -> Microprocessor -> CPU -> Motherboard -> Computer

But, it doesn't describe how the steps are performed.

[Didymus]

Simple chemicals to polymers is fairly simple. This is a diagram of natural synthesis of polymers through the relatively simple process of dehydration:



As you can see, its a fairly simple matter of the hydrogen molecule at the end of one monomer (a monomer being the 'components' of a polymer when they are not linked up. A separate amino acid is a monomer of a protein polymer.) combining with the HO from the other end of another, and a polymer is started. (the bottom half of the diagram is the opposite- hydrolysis breaking up a polymer).

Self replicating polymers are known to exist, but one of the holy grails of abiogenesis research is finding one that is simple enough to form without evolution on its side, and could plausibly do so in prebiotic conditions. It would be a lie to say that we know what this entity is, or how it formed. (by the way, this replicating polymer would be the 'life form' from which all modern life is derived, which should answer your first question.)

However, we're far from clueless. There are a number of scenarios under consideration, though all of them require far too much knowledge of chemistry for me to be able to understand them (at least, not yet: my biochemistry courses begin in only a few weeks). However, by way of example, a friend of mine once described a prebiotically plausible natural reaction that generates wholly self replicating RNA polymers. The problem is, the same reaction also generated a bunch of other stuff that destroys the new polymers just as fast. So, while we have nothing solid yet, finding this polymer and discovering how it formed could be something we hear about before the decade is done.

Once you have replicating polymers, you can have evolution, so the progression from polymer to cell can be explained largely by known evolutionary processes, helped along the way by more naturally occurring chemical reactions, such as the tendency for lipids, the fat molecules that cell membranes are made from, to both occur naturally AND form themselves into membrane and cell-like structures

[otseng]

Self replicating polymers are known to exist, but one of the holy grails of abiogenesis research is finding one that is simple enough to form without evolution on its side, and could plausibly do so in prebiotic conditions.

What exactly are the prebiotic conditions?

(by the way, this replicating polymer would be the 'life form' from which all modern life is derived, which should answer your first question.)

I'd argue if a replicating polymer is a "life form". Certainly it cannot be considered a life form from a biological point of view. I would guess that it would have to at least be in a form of a single cell.

Once you have replicating polymers, you can have evolution, so the progression from polymer to cell can be explained largely by known evolutionary processes, helped along the way by more naturally occurring chemical reactions, such as the tendency for lipids, the fat molecules that cell membranes are made from, to both occur naturally AND form themselves into membrane and cell-like structures

Please elaborate on the processes from polymers to a single cell.

[Angry McFurious]

This is what I get for sleeping in biology class.