Abiogenesis and the evolution of complex life

[sciencegirl07]

This is a question posed from me, an admitted (enthusiastic) science novice, to, perhaps, people out there who know more about the world than I do.

I would greatly appreciate if someone would explain (a simplified version) of the current theory on the evolution of complex life forms. The most common argument I hear from people who believe in creationism is that there is no way (according to probability) that complex life, or even very simply life, could have come together by chance (i.e. without an intelligent designer). From my limited understanding of evolution etc., I would say that things did not randomly come together to form complex life, but evolved to be more and more complex over time. However, I am stumped with the creation of the very first forms of living matter, i.e. the very first nucleotide bases, etc.
And then I think, why is it a necessity that non-living matter was not there in the first place (whenever that was/ if that was)?

Anyway, some light shed on the topic would be appreciated.

[Pyrotex]

Excellent question!
Let's see if I can make this brief.

First of all, it is a safe bet to start with their being no Life on Earth. Assuming that it was always here just moves the problem back further, it doesn't really help.

The Creationists are right in one thing: the chances of Life -- as we know it -- suddenly coming together all at once is so high that it's impossible. The answer is, Life didn't come together all at once. If the math says that a proposition is impossible, then the secret is to look for a different proposition.

In this case, we should look at processes where Life could come together slowly, over sufficient time, so that the "odds against" any single step are LOW enough that it's not a big deal that the step happens.

Even then, trillion to one odds are actually very doable! You see, on the early Earth there wasn't just ONE chemical experiment going on at a time, but bazillions. If we assume that every cubic centimeter of ocean water down to a depth of 10 meters, and within one kilometer from a shore, was "an experiment" -- and that a significant chemical "experiment" could occur in just one second, then in the course of just ONE YEAR, there would be over 3 million seconds, and more than 100,000 million million experiments per second. For a grand total of over 300,000 million million million experiments per YEAR! That's 3 X 10^23 experiments per YEAR.

So, even if the odds against forming a simple amino acid precursor was a billion billion to one, you could expect it to have happened around 300,000 times every YEAR in the primordial oceans!!!

The next thing to consider is that luck accumulates. As more complex molecules come into existence, they ALTER the chemistry around them. This alters the "experiments" that occur. If a molecule is built that improves the chances of more of its kind being built, then the number of that particular molecule will sky-rocket. This will change all the chemical rules, until the NEXT molecule that supports its own creation is built.

Complexity is just another word for "order". And as we now know, certain kinds of systems automatically generate order out of chaos. Thereby increasing complexity. A chemical soup of water that's not too hot or cold, containing plentiful supplies of carbon, nitrogen and salts -- with a constant supply of energy flowing through it -- is just such a system. And with over 3 X 10^23 chemical trial-and-error experiments going on every year, that's a lot of luck happening.

At some point, the chemical cycles began favoring one huge family of chemicals over all the near-infinite other possibilities. Some reactions are easier than others, and some reactions form into "loops" that are self-reproducing as described above. Such looped reaction cycles could become complex without bounds, over just a few million years.

At some point, one of these chemical cycles started forming sugars and amino acids as "waste products". Not long after that, the sugars and amino acids chained together. The first primitive form of RNA.

One cycle's waste was another's feedstock. And RNA is an excellent feedstock -- with a twist. It can store information!

At this point, you're only a handful of steps from the first truly self-reproducing "cells".

[Moontanman]

That is a very good explanation Pyro, I would rep you if I could. One thing you imply but don't actually say is that the reactions leading to life are not exactly random. The entire mechanism is not only allowed by the laws that govern chemical reactions those very laws actually make the eventual rise of replicating molecules a near certainty under the right conditions. Some chemical processes actually gravitate toward complexity naturally. Some think that most planets go through a stage where self replicating molecules can and often do arise. On most this stage is snuffed out by forces of planetary evolution but on the Earth these conditions persisted and eventually life it's self contributed to maintaining these conditions.

[ronthepon]

Actually, Moontanman, complex molecules like DNA, with their high order would tend to disintegerate. I doubt if chemical reactions would gravitate towards complexity. The explanation given by Pyro attributes the generation of these complex molecules totally to chance. Lets say that DNA actually got formed for a sec.

But how on earth did it replicate without all the wierd and complex systems that do the replication in todays systems?

I've wondered what formed first. Did the DNA come first or the DNA Polymerases and the other things appear and coincidently in the same place first?

Nod doubt, the rate at which nature experimented, as Pyro demonstrated, had a hand to all of this.

[ramanand]

Originally Posted by Pyrotex

Even then, trillion to one odds are actually very doable! You see, on the early Earth there wasn't just ONE chemical experiment going on at a time, but bazillions. If we assume that every cubic centimeter of ocean water down to a depth of 10 meters, and within one kilometer from a shore, was "an experiment" -- and that a significant chemical "experiment" could occur in just one second, then in the course of just ONE YEAR, there would be over 3 million seconds, and more than 100,000 million million experiments per second. For a grand total of over 300,000 million million million experiments per YEAR! That's 3 X 10^23 experiments per YEAR.

So, even if the odds against forming a simple amino acid precursor was a billion billion to one, you could expect it to have happened around 300,000 times every YEAR in the primordial oceans!!!

sir! i must say a very convincing and realistic explanation.
But i have some doubt regarding chemogeny ( surely no doubt regarding its occurance) but related to the first molecule (biomolecule) that had formed
in the ocean...

[Overdog]

You might find this to be an interesting article....

Self-Reproducing Molecules Reported by MIT Researchers

[InfiniteNow]

Hi sciencegirl,

I tend to prefer videos, myself. I've shared this one before, but will share it again here for you.


The one that hits your question most squarely is about an hour long (it's worth it, so grab some popcorn!). It's called "Climbing Mount Improbable."

'Growing Up in the Universe' Ep 3: Climbing Mount...

In case you really enjoyed that, I've included a link to each of the five lectures in this series for your reference. Enjoy!

Growing Up in the Universe Lecture Series

[Pyrotex]

Originally Posted by ramanand

..i have some doubt regarding chemogeny (surely no doubt regarding its occurance) but related to the first molecule (biomolecule) that had formed in the ocean...

I would like you to consider the idea that "the first biomolecule in the ocean" is not an idea that makes a lot of sense. There is no cheese going down that tunnel. There is no hard line between abionic and bionic molecules.

One should speak of biological chemical systems.

Is a simple sugar molecule "biological". Can't say. It may have occured by accident in a totally bio-free solution, and thereafter contributes nothing to any biological system.

Imagine if you will a confined volume (a tidal pool, perhaps) which is open to the addition of new fluids, gases, and recieves regular inputs of energy in the form of light (UV, visible, IR), hard radiation, lightening, heat.

Chemical action will take the form of loops. It's inevitable. There are only a finite number of atom types, a finite number of chemical bonds. So, in any sequence, where molecule A leads to B leads to C leads to D... this will eventually loop back and lead to, say B, again. You have a chemical loop. Inevitable. These loops are of all sizes, maybe even millions of steps.

But say one loop goes through molecule B and eventually leads to 2 molecules of B. This creates TWO molecular loops. Then 4, then 8. Unless other processes interfere. If not, we can see that a chemical loop (not biological) can in a sense reproduce itself.

It is only when this chemical loop is optimized, and physically contained within a tiny volume of, say, lipid molecules (which form spheres naturally) that we could BEGIN to say that the chemical loop is now showing SOME features of biological process. Is it LIFE? Prolly not--not at this simple stage.

But it is a step in that direction.

[Moontanman]

Originally Posted by ronthepon

Actually, Moontanman, complex molecules like DNA, with their high order would tend to disintegerate. I doubt if chemical reactions would gravitate towards complexity. The explanation given by Pyro attributes the generation of these complex molecules totally to chance. Lets say that DNA actually got formed for a sec.

But how on earth did it replicate without all the wierd and complex systems that do the replication in todays systems?

I've wondered what formed first. Did the DNA come first or the DNA Polymerases and the other things appear and coincidently in the same place first?

Nod doubt, the rate at which nature experimented, as Pyro demonstrated, had a hand to all of this.

I wasn't talking about RNA or DNA, those molecules came after primitive self replicating molecules came about. Life like replicating systems of things like catalysts created even more complex molecules and systems this led to life making RNA and DNA. We might not think of these early systems as life but they were the building blocks of what we now think of as life. Any time you have complex chemicals (especially complex carbon containing chemicals) with a surplus of energy you can get even more complex chemicals. this can even be seen on bodies like Saturn's moon titan. methane in the atmosphere is energized by sunlight to for bigger molecules. If the temps were higher this could be the start of even more complex molecules and catalysts which could lead to life as we know it.

[Pyrotex]

Originally Posted by ronthepon

...The explanation given by Pyro attributes the generation of these complex molecules totally to chance. Lets say that DNA actually got formed for a sec. But how on earth did it replicate without all the wierd and complex systems that do the replication in todays systems?
I've wondered what formed first. Did the DNA come first or the DNA Polymerases and the other things appear and coincidently in the same place first?....

The difficulty with these kinds of conversations is where to begin? Your post is an excellent example, so, thank you?

One must be VERY careful of one's starting point.

"Lets say that DNA actually got formed for a sec." Nope, cannot do that. Can't put one molecule of DNA in a testube of pond water, watch what happens, and deduce from THAT how DNA originated. Sure that one DNA will disintegrate in pond water. So what?

DNA did not suddenly originate in a "vaccuum". It co-evolved with all its replication and repair machinery. But this is hard to visualize.

I think DNA got started long before, in the generation of sugars and amino acids as "wastes" of one process, and these wastes were then used as "inputs" or "feedstock" to other processess. A sugar and an amino can link together.

A linked pair, sugar + amino, could link to two other pairs, to form a
TRIPLET. When this triplet encountered a certain large molecule, it triggered the large molecule to spit out a protein. These proteins did things that resulted in even more sugars and aminos, and this loop became a core feature of the local chemistry. The triplet would be the basic building block of RNA some day. The triplet in RNA codes for a specific amino acid--a sequence of amino acids makes up a protein.

Another thing was going on. A linked pair, sugar + amino, could link to yet another linked pair, in a different way: sugar + amino--weak hydrogen bond--amino + sugar.

This meant that a triplet could bond with another triplet, using 3 weak hydrogen bonds. This would be the basic building block of DNA some day: the "codon".

I imagine that in the primordial days, before real LIFE, these free floating triplets and codons served their purposes, perhaps temporarily storing "information", or serving to identify which chemical loops should be favored and which should be suppressed--behaving like a chemical "switch".

And over geologic time, the triplets and their chemical partners and the codons and their chemical support systems all co-evolved. All at the same time. So, when codons began to be linked, forming the first primitive instances of DNA, it had with it the first primitive set of polymerase molecules and enzymes and whatevers.

It is interesting to note that some biologists believe that the time between biological chemical systems and LIFE was very short, perhaps only a few million years. Or less. Or a LOT less.