Why did life on earth originate only once?

Question

The right materials for life still exist in abundance on Earth, so why do we not find new lifeforms randomly appearing out of nowhere? If it was indeed the case that life originated once in 4.6 billion years on Earth wouldn't that make life on other planets extremely unlikely?

Answer 1

Hello, there's a simple answer to your question the others missed... and I don't much care for Andrew's pantheistic answer, giving "nature" a personality and all that. There are many simplest-path rules inherent in nature but it isn't the result of a sentient choice or anything like that.



Anyway, life didn't necessarily only originate once on Earth. The first life on earth may have been multitude in origin, though admittedly it must have come from the same general source since all known life comes from similar building blocks.



The real answer to the question, however, is that after life DID arise it quickly adapted to environments. These adaptations did two things to prevent the abiogenesis of further life:



1) The life that already existed would far outcompete primitive or proto-life that may have formed or almost formed, preventing the resources from accumulating to cause abiogenesis a second time by consuming the resources or even the proto-life themselves



2) Life can drastically alter the conditions in an area, just look at how Earth is now a nitrogenous-oxygenated atmosphere, which is extremely, extremely different from what it used to be. These changes can be local as well as global, and any tiny change can probably move conditions away from "just right" for life to form



Hope that answers your question!

Answer 2

1. We do not know that it "only" originated once. There are still bacteria around that clearly originated when there was no free oxygen on Earth. However, that is rare, bringing us to:



2. There is a dominant life-form that took control of the environment. When plants took control and transformed Earth's atmosphere by dumping all this oxygen "pollution", that pretty well settled it for any newer form of life. It became very difficult to create conditions that would make it probable to assemble (different types of) long molecules with the ability to reproduce themselves.



3. By the time the "original" lifeforms had taken over, many chains of molecules had been pre-arranged (enzymes, proteins...). This greatly favored the formation of available atoms into molecules that had magnetic signatures (weak bonds) compatible with existing molecules. That would make it very difficult to find sufficient "free" atoms to assemble in types of molecules that would be substantially different than the ones that had taken over.



4. Once a different life form exists (if it ever does), it has to "feed". If most of the existing molecules that can provide chemical energy are already assembled with a magnetic signature compatible with the existing dominant lifeform, they might not be available as "food" for the newer lifeform.



A bit similar to the question sometimes asked in s-f stories: if we land on another planet and we see plants, will it be food for us, poison, or simply inert (i.e., we would be unable to assimilate and digest it). Even on this planet, there are plants on which other animals can feed, but that would provide humans with no nutritional value at all (e.g., wood).

Answer 3

Think of life as a machine. Over a billion years two pieces of metal came together just right to form a lever, todays life being HAL. Similarly, life wasn't much in comparison to todays life. It was probably just some random organization of molecules that just happen to lend itself to self-replication. Over time one of these replicating molecule groups added a new molecule which maybe kept it in ideal temperature water for longer. This group of molecules then grew into larger numbers until another random change allowed it to become more successfully at self-replication. This is evolution



You are right that life in that form has probably come about before. However it is still extremely rare and all those organic compounds are now in use by every living thing on the planet making it a much rarer occurrence. If it did happen it would have been snuffed out by the highly competitive life forms of today. If some poor sap in a village somewhere in the middle of the forest re-invented the wheel do you think it would have much of an effect on the world when there are cars and planes everywhere else?



Hope some of this helped

Answer 4

Ok think about it, of course life out there will appear; you cant say the chances are too small (we are here arent we?) the universe is according to most teories infinitly big so that would make the chance for life quite big.

But how far into space have we atually looked? not very far, not even a pinhead size relative to the sun. so we will not have seen them/him. We are searching for x rays and stuff, but the way our searches goes if we were on our closest soler system and looked to the human race on earth with our telescopes we would not have detected life on earth.



Exept the religious views of course then we are unique



But tricky question about why lifeforms doesnt appear randomly on earth! only way would be that they all start out as cells, and we already know all the cell forms so we expect them all to appear. very good question

Answer 5

Life only needed to form once here. After that, the effects of life and other factors started to change the Earth's environment, and the newer environments were not as conducive to the forming of new life.

Then, once life got enough of a grip here that we had multi cellular life, and even more complex forms, there was no room for new life to form in the first place.



Its that the processes for the origin of life are so ubiquitous that suggests that the possibility of life is high in most occurances where you get the appropriate conditions for it.



If you want to know more, the Biology section is the appropriate place to ask in.

Answer 6

Wow good question! In fact you answered your own query in your question. New life is created all the time through the process known as evolution. However, the reason why spontaneous life just doesn't happen today is because nature is lazy, so to speak. Nature will choose the simplest and smoothest path to create something, (why have 5 eyes when two will work just as well), so nature would rather continue building up on the current biosphere rather then repeating the process and starting from the ground up.

Answer 7

While we may not see things immediately that most average folks would consider "life" we do find new species frequently. Unfortunately, far less often than we find species are becoming extinct. As far as life on other planets, I have a hard time imaging it doesn't happen. It may not be life as we recognize at first, nor life that survives under the same conditions that we do, does not make it any less "alive".

Answer 8

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It's not known that it did origniate only once. Rather, all known organisms appear to share common ancestry. That doesn't rule a couple of possibilities. Firstly, one lineage of organisms proved more successful than another or other lineages, and shoved them out of existence. Secondly, and presumably less probable, other lineages are out there somewhere awaiting discovery.

Answer 9

we don't know that it did.



our life shows clear descent from pre-cambrian life forms. we don't know what happened in the early days. one thing we know is that nature tried many variations on life before settling on one. some of the most successful cambrian life forms (trilobites) were, as the name suggests, 3-way symmetric, not two-way like we (and all mammals, birds, insects and reptiles) are.

Answer 10

the right materials may exist, but the conditions do not. these conditions can be recreated in a labratory, creating life artificial is the holy grail of science; most believe it is only a matter of time

Answer 11

there are two answers:

Biblically-God created us specifically on earth. it is called the divine theory.

scientifically-scientists say that the earth had the perfect environment for life to grow. there is a theory that one meteorite crashed into earth bringing the main organic chemicals; oxygen, carbon, nitrogen and hydrogen.

Answer 12

Perhaps it does still happen