Eli5: (This prob sounds stupid) How did life forms come to be on earth? Like, how did something become ‘living’?


Eli5: (This prob sounds stupid) How did life forms come to be on earth? Like, how did something become ‘living’?

In: Biology


This isn’t a stupid question. Science itself cannot explain how life came from nothing. Seriously, every experiment ever devised by humans to try and create life from non-living matter has utterly failed. The probability of life happening from non-life is so infinitesimally small (one in a trillion, trillion, trillion, trillion, trillion, trillion [72 0’s]), that we cannot actually calculate it.

There are two schools of thought for how life came to be on Earth:

1. Random chance: all the building blocks of life (at least 250 proteins aligning in the correct order) were available on earth and lined up perfectly for the first single-celled organism to exist.
2. Creationism: All life suddenly and wonderfully came into existence at the creation of a divine being.

The data we have in fossil records support #2 more than #1. But, I’m sure this will get down voted into oblivion.

Remember in primary school when the teacher said that proteins are the building blocks of life? When certain proteins combine with other organic matter they can form cells. Life does not equal thought or consciousness. Life is simply organic cells that can split and make more of themselves. Super complex life took billions of years of stressors that only the adaptable could survive. But, for the original life on Earth, it was the high likelihood of these organic molecules combining and forming cells. The high likelihood was also dependent upon the amount of carbon dioxide and sunlight present.

That is actually still a topic for debate.

It is generally assumed that at some point simple chemistry of self replicating molecules turned into life. We think that the very first life was RNA based not DNA based as you and I are.

There is some debate exactly where that happened. Tidal pools were a popular location for a long time, but deep sea vents are also a serious possibility.

There is also the whole panspermia theory (don’t laugh that is what it is called). The idea that life didn’t get started here on earth at all, but rather was contaminated by asteroids that contained some primitive life that originated elsewhere.

The idea that life got started out there does nothing to help solve the problem of how life got started int he first place and merely moves the problem to another location, but it has huge implications for the chances of findign life elsewhere.

A basic chemical reaction might go a bit like this:

A + B = P

You mix two things together (reactants), they combine to make a new thing (product)

How fast this happens depends on a few things like heat and concentration of reactants and the general reactivity of the chemicals involved. Different reactions go at different speeds. Some happen in a matter of moments, others can take years.

So if you’re in chemistry class and you want a reaction to go faster, you might heat up your beaker rather than wait around.

Another way of speeding up a reaction is to add a catalyst. Catalysts are a type of substance that increases the rate of a reaction without themselves being changed.

Enzymes are good examples of catalysts, and you’ll also find them in the catalytic converters on cars.

So your reaction might look a bit like this:

A + B + C = P + C

So you get your catalyst back after the reaction, and it can go on to catalyse (speed up) another reaction. It doesn’t get used up like A and B.

Catalysts are chemicals like everything else, so they too can get formed by chemical reactions. So can you have a catalyst for a reaction that makes a different catalyst?


But what happens if the catalyst for making the catalyst is itself the same catalyst?

A + B = C (slow)

A + B + C = C + C (fast)

You would quickly end up with a lot of Cs because every C you make helps make more.

So this is what happened in the primordial soup. At some point, a molecule formed that was a catalyst for it’s own creation and started making more. (chemicals don’t have a “choice” whether to react, they just do if the conditions are right)

In a sense, these molecules started competing with each other for those reagents, A and B (in this case the reagents are amino acids). Slight changes to the catalysts made them more efficient or faster or resilient to other chemicals, which in turn meant that more of that particular version of the catalyst was made.

Bit by bit, the catalysts became more and more complex, and started coating themselves in lipids to protect themselves, made systems that only allowed proper reagents through that lipid barrier and developed ways to break down bigger molecules back into amino acids. Millions of years pass and the catalysts have gotten so complex we get the first cells.

Because that is essentially what DNA is. A chemical that catalyses the reaction to make more DNA. Our lifecycle is a bit more roundabout than that now, but in a pure sense it is true. Life makes life. A catalyst that makes more of itself.

We don’t know for sure but the current theory is that random chemical processes created a self-replicating molecule and that was enough to start evolution.

You really only need one, because in an environment without any other life it can replicate without any competition. The replication process would be far from perfect in such a primitive “life” so the rate of random changes (mutations) would be very, very high.

Imagine you have 2 unknown molecules A and B that attract each other. On their own they are very simple and can be created by random chemical processes. But once they connect together you have AB. Then maybe ABBABBAAABBABB or whatever. Now, the same molecules can maybe randomly attach to the sides of the chain and then get torn off later, and voila, you have a self-replicating system. Some of the sequences are more likely to undergo the replication, so they dominate and the evolution begins.

We can’t research it because we don’t have the millions of years it took to get from something unbelievably simple to anything that we’d call life today.

Creationists these days argue that the chance of creating a protein randomly is so vanishingly small that it would not happen even in billions of years. They may even be right. But proteins are already complicated effects of evolution, whatever came first had to be much simpler than that.

Imagine this thought experiment: you throw 1000 6-side dice and expect to have a result of exactly 1-6-1-6-1-6-1-6 and so on for the whole 1000 dice.

The chance of it happening randomly is 6^1000 which is truly impossible within the time available in the Universe. But, what if dice have magnets inside so that if 1 and 6 land next to each other they get permanently attached? Well, now all you have to do is keep shaking the dice and eventually all of them will align, pair after pair.

Oh, that’s a good one, I’ll give it a shot.

The short answer is, we don’t know for sure and if someone did, I’m sure Nobel Prize would be coming shortly after.

The difficulty comes from identifying the exact point of when something is “alive” and “dead”.

Today we can observe RNA (building block of virus and a sister to DNA of you and me) does remarkable things but it must have a host. It doesn’t do anything on its own. In order for virus to replicate, and we seem to agree that reproduction is a big part of “alive”, it needs more.

By contrast DNA does the reproduction on its own, it can create more of itself. How did it do that? When conditions were “just right”. What are those conditions? We still don’t know for sure.

So, how did we get from inorganic mix of chemicals to a living cell? A few theories have been proposed, including the “just right” conditions of tide pool or close to thermal underwater vents (temperature, pressure, etc) and a _lot_ of time.

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