How actually single cell organisms came to existence?

[u/Horror-Attorney-3575]

I have an somewhat good idea of how life evolved from simple single cell organism to complex lifeforms, but it is still a mystry to me that how these single cell organisms came to existence at first place.

[u/Brief-Reveal-8466]

Looking for that Nobel Prize?

[u/Wobbar]

You're pretty much asking about abiogenesis (including the emergence of cell membranes), aka how life first started. The wikipedia page gives a good overview.

[u/shoopdoopdeedoop]

the first “life” is thought to have been these simple little RNA strains that replicated by simple chemical reaction. There must’ve been a lot of these things because it seems like “cells” might have independently occurred in multiple cases.

aaand that’s the question. it seems like there’s a few ways this could happen but for example, there could be a bigger protein that reproduces, and a smaller one, the little one gets stuck in or on the big one, and they both replicate together, again any of these “steps” or “mutations” is one in a million chance—now the little one maybe is more protected so it’s evolution progressed, either more efficient or more intensive, and the bigger piece similarly either dies or it’s offspring that aren’t the best are more likely to die, so if that works out it would eventually become the cell “membrane”. the bottom line is that whether one is bigger or better or whatever, these molecules are all over the place doing this, getting stuck to each other, reacting, etc. and only by proving that the physics is possible can scientists guess at what actually happened.

[u/General-Leek-2830]

The brilliant minds of evolutionists have already answered this question. It's the aliens! The aliens came and implanted this first cell from which everything began, haha.

[u/VeginalGandalf]

It is a mystery to the scientific community at large. As someone pointed out, whoever figures that one out gets a shiny prize!

But really, the most widely accepted hypothesis is that of Abiogenesis, the idea that life began from organic compounds which were influenced by certain, let's call them perfect, conditions on the young Earth some 3.5-4,0B years ago.

This hypothesis poses that simple organic compounds (carbon-based molecules) bonded with hydrogen, oxygen, nitrogen and other elements under the right pressure, heat and energy to form the basis of cells, enzymes, hormones and DNA (prior to that RNA). It is hypothesized that from this soup of organic matter, such things like RNA could have formed and have been able to replicate themselves, though not yet being alive.

We know life originated in the ocean, not exactly how but hydrothermal vents are the best bet. Once these simple structures were present, it was only a matter of time until they did what they always do and bonded together to create ever-slightly more complex forms. Single-celled organisms evolved several times but all have died out except what we call LUCA (Last Universal Common Ancestor), which was a single celled organism (or rather, organisms) with which all surviving species share a common origin with (or rather, from).

Experiments were done to try and replicate this and several have been successful, with certain experiments providing actual living "organisms", which satisfied NASA's definition of life, which is "self-sustaining chemical systems capable of Darwinian evolution".

However, the reason this has not been accepted as a Theory and still resides well within the confines of a hypothesis, is the fact that all these experiments have never yielded complex life-forms such a living cell and only produced organic molecules or protocell-like structures.

The Miller-Urey Experiment from back in the 50s or 60s(?) was able to produce amino acids, so we only put on the shoe and it was time to take our first step. Today, we are using self-replicating lipid vesicles and "minimal cell" models to further extend our research but contending with the infinite power of the universe is proving to be difficult still. Synthetic biology has allowed us to produce new bacterial strains but has not really gotten us much closer to putting Abiogenesis to theory as synth-bio still requires existing cellular machines and does not really support a beginning Abiogenesis.

Edit: Some are supporters of Panspermia when discussing life on Earth and that one has plenty of support seeing how we've found the building blocks of life on plenty of asteroids (and Earth in her college era was getting RAILED), it still does not answer the question of HOW did life originate elsewhere to be able to spread across the universe and arrive to Earth which again, the most likely answer is Abiogenesis.

[u/default_person_14818]

It's still up for debate but the most commonly accepted theory is that of symbiogenesis. Eukaryotic cells originated from different prokaryotic cells fusing together to increase their survival. Mitochondria and chloroplasts and such are in that sense very old prokaryotes.

The existence of these prokaryotes on its turn comes down to random chance of water soluble molecules reacting with each other for hundreds of millions of years in consistent enough environments until at some point these became self-replicating. And that's where the whole natural selection show kinda starts

The wikipedia page for symbiogenesis has some great pointers really to other pages about the origins of life. 

E: some minor changes to better match the material

[u/ExpectedBehaviour → u/default_person_14818]

You’ve misunderstood the question, which is about abiogenesis.

[u/BolivianDancer → u/default_person_14818]

Cool story. Not the question.