/sci/ - Science & Math

>>1990389
There's the thread.

Putting that question another way, why can't we observe early forms of life now ?

>>1990582
Because the environment has changed.

>>1990582
We can. They are part of the biological processes that take place in your body all day every day.

>>1990582
nolongerprimordialearth.jpg

>>1990582
Competition OP.

Early life was very basic, it just wouldn't be able to compete against the more complex life we have now.

>>1990607
How is the current environment more hostile to primitive life forms than it was 3 billion years ago ?

>>1990619
There they are part of a life form that is a product of a long evolutionary history. Is there similar stuff happening on their own ?

OP, it's quite possible life originated more than once, but the available components and conditions would have been pretty much the same, so at its simplest form one novel organism would have been much like another.

Also, as soon as the first organism began to take hold in its environments it started using components necessary for life, thus making it less likely that new life would assemble in that environment... and presumably the environments capable of producing and supporting simple life were quite limited.

It only needed to happen once to explain current results, but as you say if it happened once it could happen again. We probably couldn't know if it happened more than once, though we do know that organisms fairly quickly changed their environments in ways that make a recurrence unlikely.

>>1990630
This. Early life needed the conditions of primordial Earth, particularly the reducing environment (as opposed to oxidizing today).

In regards to your question, I suggest this way of thinking about it: DNA is just one way to encode information. There's nothing particularly special about. A different molecules or different nucleotide bases could have been use. However, every living thing has DNA as its genetic material. This is one thing that leads us to believe that all of life had a single origin.

>>1990660
I assumed that competition between self-replicating proteins was not that intense.

>>1990697
I meant at the ecological level of self-replicating proteins.

>>1990669
Early life forms didn't like oxygen much.

Actually, it may have arisen many times, but the other forms went extinct--just as dinosaurs, trilobites, etc. In addition, although all the eukaryotes likely share common ancestry, the bacteria and archea may be separately originated life forms.

>>1990559
>If it happened once, it should happen more than once, no ?

It most likely happened twice or even more often. The problem is there was already life around when it happened again. Life eating the nutrients or even the new life.

Bacteria are still the most common form of life on Earth living all around us and everywhere.

>>1990582
Survival of the fittest. The old ones are the fittest.

>>1990690
Hm. How long did that reducing environment last ?

>>1990755
Until the so called "Oxygen Catastrophe"

http://en.wikipedia.org/wiki/Great_Oxygenation_Event

Well okay. Thanks.

>>1990763
>around 2,400 million years ago
That makes more than one billion years of appropriate conditions...

>>1990787
Correct, but, like others have been saying, life could have arisen more than once. It just appears to us that one lineage, out of all of the lineages that could have arisen, drove the others to extinction (if there were others). It's not that there <span class="math">couldn't[/spoiler] have multiple origins, it's that the evidence suggests that there <span class="math">wasn't[/spoiler] multiple origins.

>>1990801
*weren't

>>1990801
Great info File. I think you're officially my favorite trip on /sci/

>>1990813
You're welcome!

There are other lifeform patterns, they are just so different from us that most do not recognize them as life. They are called Viroids and Pryons. Neither transmit information like DNA-based life but both are self replicating patterns (pryons do not really vary however). It is also arguable that other lifeforms exist as neural patterns within human brains. Like all lifeforms these patterns reproduce themselves with variation and undergo selective processes.

In otherwords we see only one life because we define life myopically and in regards to form not pattern

>>1990801
Ok.

On a side note, italics ? On my 4chan ?

>>1990840
[ math ] words [ / math ]

Remove all the spaces from the above.
If you want to put spaces between words in the brackets use~the~tilda~key.

>>1990840
Oh. It's the scientific notation thing of /sci/ ?

>>1990850
Decidedly an instructive thread for me. Thanks.

>>1990852
Yep. Useful for actual math as well (like the equation for a Leslie matrix):

<span class="math">\mathbf{n}_t=\mathbf{L}^t\mathbf{n}_0[/spoiler]