How Did Life Begin on Earth and Could It Happen Elsewhere?

[wolram]

can anyone tell me what the latest theories are on how
life began on Earth ,and on the posibility of the same
sequence of events occurring on other planets?
and did plant and animl life evolve from the same "soup,"
if so why are they so different?

 

[Chemicalsuperfreak]

To make a long story short, and I may have some details incorrect. The early terrestrial atmosphere was reductive, it could produce many simple biological molecules such as amino acids, peptides, nucleic acids, and self assembling phospholipid bilayer membranes which can grow and reproduce by budding. This has all been done in laboratories. The theory is that over time all these components aggregated into simple life forms with RNA as genetic material and a 2 codon genetic code. The big differences that evolved over the next 4 billion years were a switch to DNA, a three codon system, and the advention of sex.

Every living thing evolved from that soup.

Why are plants and trees so different? When you look at it objectively, we're really not very different.

 

[Monique]

Originally posted by Chemicalsuperfreak
Why are plants and trees so different? When you look at it objectively, we're really not very different.

Are you kidding me?? Plants and animals evolved independently! We DO share some chemistry, so there IS a common ancestor..

The latest theories.. aliens, god, space dust, primordial soup, atmosphere, deep sea vents, chemical caves, and a few days ago Ivan Seeking came with a link that scientists were looking at clay for the origin of life.. beats me..

Chemicalsuperfreak, you are putting things too simple. The aminoacid generation experiment you are talking about is actually quite controversial, contamination has been the suspect..

Who says RNA was the starting material, later switching to DNA? Two codon genetic code? Just askin' :P

 

[Monique]

If you were asking about my opinion, I'd say I like the deep sea vent idea the best.. high pressure, lots of rich chemicals bubbling from the inner earth, high temperatures, circulation, I can envision DNA replication down there..

 

[Chemicalsuperfreak]

Originally posted by Monique
Are you kidding me?? Plants and animals evolved independently! We DO share some chemistry, so there IS a common ancestor..

The latest theories.. aliens, god, space dust, primordial soup, atmosphere, deep sea vents, chemical caves, and a few days ago Ivan Seeking came with a link that scientists were looking at clay for the origin of life.. beats me..

Chemicalsuperfreak, you are putting things too simple. The aminoacid generation experiment you are talking about is actually quite controversial, contamination has been the suspect..

Who says RNA was the starting material, later switching to DNA? Two codon genetic code? Just askin' :P

Animals and plants are like humans and chimpanzees. There is a lot more in common than different. Animals and plants share what, like 70% of their genomes with each other? Same genetic code, same essential cell structure, same major biochemistry. The only major difference is a few biochemical pathways which plants have and animals lack.

The Miller/Urey experment is widely accepted. It has been repeated and expounded upon to include the primordial synthesis of all 20 major amino acids. In addition to other major biochemical players, such as ribonucleotides, which is part of the reason why RNA is believed to be the precursor to DNA.

The very genetic code suggests an earlier two codon system. The degeneracy of major aminoacids implies as much. I believe there is much greater evidence for this theory in the mechanics of transcription, replication, and proofreading.

 

[Monique]

Originally posted by Chemicalsuperfreak
Animals and plants are like humans and chimpanzees. There is a lot more in common than different. Animals and plants share what, like 70% of their genomes with each other? Same genetic code, same essential cell structure, same major biochemistry. The only major difference is a few biochemical pathways which plants have and animals lack.

No, I don't believe that. Could you give me a citation of the 70% identity?

Plant cells have cell walls, eukaryotic organisms don't. Plants are specialized to get energy from light, eukaryotic cells are specialized to get energy from organic sources. The receptors for cell communication have similarities, but eukaryotes mainly use G proteins, plants thyrosine receptors (I believe). Have you ever seen a plant used as a model organism for humans??

Eureka! Why use lab animals?? Let's use plants since we have more in common then they are different.. sorry for the sarcasm :P

Does a plant have organs besides the reproductive ones? Do animals have roots? The macro structures are very different too.

How many billion years ago did plants diverge from animals?

 

[Monique]

The 70% identity is very hard to believe, are you talking about genes or genomes? Plant genomes alone differ greatly, some are very large (rice) some are very small (Arabidopsis thaliana).

Besides that, humans differ in 99.9% of their genomes, humans and chips probably something like 98.7%. 70% would be a huge difference.

Even humans and mice differ in crucial ways. Today I was reading a dissertation, where a mouse model was attempted for a lysosomal storage disease. Lacking an active enzyme, the substrate piles up in macrofages in humans. When the same enzyme was disabled in mice, the phenotype did not occur, turned out the mice had an alternative route that could get rid of the substrate.

 

[Chemicalsuperfreak]

Originally posted by Monique
No, I don't believe that. Could you give me a citation of the 70% identity?

Plant cells have cell walls, eukaryotic organisms don't. Plants are specialized to get energy from light, eukaryotic cells are specialized to get energy from organic sources. The receptors for cell communication have similarities, but eukaryotes mainly use G proteins, plants thyrosine receptors (I believe). Have you ever seen a plant used as a model organism for humans??

Eureka! Why use lab animals?? Let's use plants since we have more in common then they are different.. sorry for the sarcasm :P

Does a plant have organs besides the reproductive ones? Do animals have roots? The macro structures are very different too.

How many billion years ago did plants diverge from animals?

Well, chimpanzees have a different number of chromosomes than humans, and they have lots of hair and are good at climbing trees. My point is that we have a common ancestor and we are not that much different if you look at it from an outside perspective. The only major difference is that plants use photosynthesis and animals eat plants to get carbohydrates. Most of the other differences such as cell walls, andronergic receptors, leaves and muscles, have evolved because of this one difference. At the basic level we're practically the same biochemically, we both eat, drink, breathe, screw, and die. We just have slightly different ways of going about the whole process. The original question was wondering, basically, how could there be a common ancestor if plants and animals are completely different. And in the big scheme of things we're not completely different. Like I said, we have more in common than in difference.

 

[wolram]

thankyou for your replies monique, chem.

but i am now more confused, i like the idea that life
started in some deep sea hydrothermal vent "lots of mixing".
i don't know what fossil records show about the first
living things or if they ever were fossilised.
i can understand the very earliest life fed from chemicals
it must have been a major divergence when animals started
to eat plants.
sorry if my terminology is wrong.

 

[wolram]

i found this on the net,


http://news.nationalgeographic.com/news/2003/01/0130_030130_originslife.html

First, the researchers hypothesized, biological processes produced and deposited fatty molecules along the inner surfaces of the iron sulfide cavities. Eventually, these fats formed into cohesive membranes that fully enclosed the biological activity inside. Archaebacteria and eubacteria arose independently from parallel occurrences of this series of events, Martin and Russell proposed.
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in another paragraph it states that only rock and water are
needed for life to emerge.

 

[Another God]

I agree with CSF in thinking of plants and animals as similar, but I don't know about the 70% genome similarity thingy. The way I look at it, Eukaryotic cells originated and perhaps even started producing multicellular organisms, and somewhere down the track one line of these eukaryotes picked up a chloroplast. That was the beginning of the divergence of plants from animals. We still come from the same eukaryotic lineage, and that in itself means that originally we all had the same sorts of genome processes, mitochondrial functions, ER, Golgi etc... We are very similar because the cell is the basic unit of life, and cells tend to be very similar in all life. While the way the cells come together vary drastically, they are all still very similar cells.

I am sure the cell wall etc are consequences of the gradual evolution towards adapting to their new method of survival.

Who says RNA was the starting material, later switching to DNA?

It is a very reasonable theory. RNA is afterall capable of acheiving everything DNA does, plus it catalyses its own copying (rRNA), its own translation (tRNA) and it is its own messenger (mRNA). In a haphazard system, it makes sense that RNA should hold its own code. DNA's only purpose is to stabilise the system into a double stranded system slightly less prone to nucleation.


Wolram, I have always thought that the deep sea hydrothermal vent idea was neat. It seemed a perfect condition for containing all of the necessary chemicals and the hot/cold alterations that can so assist the processes of life. (Do you know what PCR is? This is sort of how I imagine primordial life may have started). If you look around at the other threads in this forum though, and find Ivan Seekings post he has a link to an article that proposes it may have started in clay pools rather than deep sea vents though. I have no reason to really believe either yet, and of course more study is being done.

As for fossilization: No. Inverterbrates don't really fossilize...stromatalites are the only species I know of that have left behind traces of their existence, but that is a by-product of their existence (calcium piles i think?) not a fosilization of their actual bodies... Typically you need bones etc for fosilization to occur (and even then its incredibly hard to make it happen), and cells (or even worse: Proto cells) do not make the cut.

All life 'feeds on chemicals' to some extent or another

Animals eating plants, just like plants eating animals, just like bacteria eating bacteria is just part of nature. It always has been and always will be part of the natural system. The divergence between plants and animals would have been an evolutionary fluke, without any real significance at the time...As with basically all evolutionary divergences.

 

[Guybrush Threepwood]

Originally posted by Chemicalsuperfreak
The Miller/Urey experment is widely accepted. It has been repeated and expounded upon to include the primordial synthesis of all 20 major amino acids. In addition to other major biochemical players, such as ribonucleotides, which is part of the reason why RNA is believed to be the precursor to DNA.

yes, but I understand that the hydrogen taht was used in the miller experiment could not exist in the early Earth atmosphere because the Earth's gravity is to weak to hold it. All the hidrogen propably escaped into space early while the planet was still too hot.

 

[wolram]

from another god

Wolram, I have always thought that the deep sea hydrothermal vent idea was neat. It seemed a perfect condition for containing all of the necessary chemicals and the hot/cold alterations that can so assist the processes of life. (Do you know what PCR is?

sorry i have just blundered in here to learn a little about
how life began, foolish or what? i will have to learn a lot
more befor i even know what you are talking about

 

[Monique]

he was just trying to help Wolram, let us know when we are talking incomprehensible lingo :P

The reason that the deep sea hydrothermal vents are attractive is the reason that there are temperature gradients that mix ingredients. And where ever there is a gradient, vortexes will be created right?

A piece of genetic material will go from a very hot environment to a colder environment, to a hot environment. Such cycling causes the denaturation of biological molecules.

PCR what he was referring to stands for 'polymerase chain reactiong'. It is the reaction whereby we duplicate our DNA, this recreated in the lab everyday by temperature cycling, the same temperature cycling that could happen at the vents!

 

[wolram]

thankyou MONIQUE.

i must say with my "limited knowledge", that hydrothermal vents
seem better than mud for life to start.
has anyone come near to producing life in the lab?

 

[wolram]

http://www.spaceref.com/news/viewnews.html?id=463

As such, from the perspective of a substantial portion of the life on Earth, the ability to live in an aerobic (oxygen rich) world confers upon our own species the distinction of being an extremophile. But there are other things that organisms can "breathe". The bacterium Shewanella putrefaciens uses metal atoms in its metabolism in the same fashion as we use oxygen atoms. As such, it "breathes" metal - in this case, manganese.
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this may be old, but i have found it facinating, its sort of
opened my eyes, life in all it variations.

 

[Monique]

Yes, those are called chemothrophic autotroph, they still exist today and live in underground caves. Live forms not dependent on sunlight have only recently been identified.

Chemotrophic autotroph. Organism in which energy is obtained from endogenous light-independent reactions involving inorganic molecules.