PDA

View Full Version : Potentially dumb question about origins of life on Earth.



Buttercup
2014-Jun-06, 03:51 PM
Does evidence point to life on Earth originally starting in one spot OR taking root all over the globe simultaneously?

Thank you for any and all input. :)

Extrasolar
2014-Jun-06, 04:03 PM
Does evidence point to life on Earth originally starting in one spot OR taking root all over the globe simultaneously?

Thank you for any and all input. :)

Of course, I don't know, but I've wondered about this too and came to the logical conclusion that it started in one place and spread. Our brand of life could have possibly destroyed other life that also came into being as a result of resource competition. A recent paper came out recently where scientists added 2 components to DNA and found that the new "neo-nucleotides" propagated to the next generation of offspring.

http://www.nature.com/nature/journal/v509/n7500/full/nature13314.html

I suspect that (based on this experiment) that "life" is at least possible in other forms (which says nothing about probability).

Noclevername
2014-Jun-06, 04:26 PM
Does evidence point to life on Earth originally starting in one spot OR taking root all over the globe simultaneously?


There is currently not enough evidence to say for sure. Only a few bits of the earliest rock on Earth remain, and only in a very few locations. The rest of the crust has been recycled and/or eroded away numerous times. Also, the earliest evidence of life is not clearly dated, only that it happened somewhen around the time the oldest rocks were formed.

Squink
2014-Jun-06, 04:57 PM
The mapping from codon to amino acid (http://en.wikipedia.org/wiki/DNA_codon_table) is darn near universal, except for a few exceptions in organelles such as mitochondria (http://en.wikipedia.org/wiki/Mitochondrion#Genome). Although the codon table we have is a pretty good one, there are literally zillions of other tables that could have come about, so the existence of a single table in all organisms is good evidence that life only ever came about once, or that having arisen several times, one particular genesis outcompeted all the others to the point of extintion.
Recently, a small fraction of organisms have been found ignoring some stop codons (http://www.the-scientist.com/?articles.view/articleNo/40048/title/When-Stop-Means-Go/), but 63 of the 64 possible codons in these organisms still retain the standard coding, so it's probably a case of after-genesis modification, as with mitochondria.

Ara Pacis
2014-Jun-06, 05:41 PM
Besides a competition-extinction hypothesis, one might consider a collaboration-fusion hypothesis. In the former, similar or different processes cause lots of separate genetic lineages to develop and one beats the others and wins out. In the latter, similar processes causes lots of separate genetic lineages, but they are similar enough that they tend to merge and incorporate their codes into new entities. For former may be considered functionally similar to how species fight for survival in the macro world. However, the latter might be considered functionally similar to how bacteria exchange genetic information through plasmids and how virus DNA can become stuck in the host's nuclear DNA.

danscope
2014-Jun-06, 06:50 PM
I think it is quite likely that we got our water from a massive bombardment of comet-like objects over a period of time,
with some of the right sized pieces surviving , such that they landed in the new oceans, life of some sort thawed out and propagated therein. Just a theory. Goldilocks objects for a Goldilocks Zone.

Squink
2014-Jun-06, 06:57 PM
I'm a fan of panspermia myself danscope. Proks in a couple hundred million years, then a delay of billions to get to euks? Seems implausible.

Ara Pacis
2014-Jun-06, 07:19 PM
I'm a fan of panspermia myself danscope. Proks in a couple hundred million years, then a delay of billions to get to euks? Seems implausible.

Assuming that's what happened. Do we have enough paleo-archeological evidence? What if there was a reason for a separation of the two, such as segregated basins or a snowball earth icecap?

Squink
2014-Jun-06, 09:44 PM
one might consider a collaboration-fusion hypothesis.Ever tried running Z80 (http://en.wikipedia.org/wiki/Zilog_Z80) assembly language on a 6502 (http://en.wikipedia.org/wiki/MOS_Technology_6502)?
It's not a winning proposition.
There's no evidence of any naturally occuring system that allows for translations between different codon tables.
That being the case, a gene that codes for a highly efficient cytochrome c oxidase (http://en.wikipedia.org/wiki/Cytochrome_c_oxidase) using the codon table that all current organisms use, will produce garbage if it's fed an mRNA that codes for a highly efficient cytochrome c oxidase when translated through a completely hypothetical different codon table.

Noclevername
2014-Jun-07, 04:07 AM
I'm a fan of panspermia myself danscope. Proks in a couple hundred million years, then a delay of billions to get to euks? Seems implausible.

Why? Evolution is partly random, after all; it does not conform to a timetable. The particular symbiosis that led to eukaryotes might never have happened at all had some proto-mitochondrial symbiote gotten into the wrong host, or vice versa, or just drifted a few millimeters too far to the left and missed its chance to hook up.

Swift
2014-Jun-07, 04:24 AM
Besides a competition-extinction hypothesis, one might consider a collaboration-fusion hypothesis. In the former, similar or different processes cause lots of separate genetic lineages to develop and one beats the others and wins out. In the latter, similar processes causes lots of separate genetic lineages, but they are similar enough that they tend to merge and incorporate their codes into new entities. For former may be considered functionally similar to how species fight for survival in the macro world. However, the latter might be considered functionally similar to how bacteria exchange genetic information through plasmids and how virus DNA can become stuck in the host's nuclear DNA.
That would be my guess, or something similar. It seems more probable than all life evolving from a single event at one site. But, as others have said, we have little evidence.

I've never been a fan of panspermia. You still have to have life originate someplace, and have just added the further complication of transporting it to Earth.

Oh, and Buttercup, a very not dumb question.

dgavin
2014-Jun-07, 08:59 AM
There are a few hypothesis that suggest life might of started with methane loving organism's that made use of chemosynthesis, and that our current photosynthesis based ecosystem developed as oxygen and Co2 became more available then methane.

Swift
2014-Jun-07, 12:44 PM
There are a few hypothesis that suggest life might of started with methane loving organism's that made use of chemosynthesis, and that our current photosynthesis based ecosystem developed as oxygen and Co2 became more available then methane.
And if not methane, some other chemosynthetic pathway.

icefoxen
2014-Jun-10, 04:44 AM
And if not methane, some other chemosynthetic pathway.

There's a lot more of these than you might think. A neat paper (I think it was http://dx.doi.org/10.1016/j.gca.2009.08.036 or a followup to it) describes all the possible chemical reactions possible that release energy, just starting from the chemicals in a sample of hot spring water. There's something over 300 of them, and for each one, there's some kind or organism or another (or usually many) that can use that reaction to "eat" the chemicals involved and gain energy from them.