Stanley Miller's experiment was an amazing step forward in unifying inorganic and organic chemistry. It was also a landmark development for the theory of chemical evolution.

Miller-Urey Experiment

However what if the experiment was done at planet scale? Some trillion years later humans decide it would be nice to play god with another planet and decide to carry a planet scale experiment (And they can do that since they are highly advanced by now). They create a red dwarf and put it up with a planet which basically happens to be a planet scale recreation of miller's experiment.So My basic question is

How long does this planet take to evolve intelligent life (If it ever does) ?

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    $\begingroup$ Does it have to be that experiment? Later experiments were far more successful. $\endgroup$
    – Feyre
    Commented Nov 8, 2016 at 12:35
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    $\begingroup$ I'm not sure if alternate-worlds is right here, I've added evolution as that should definitely be here. $\endgroup$
    – Tim B
    Commented Nov 8, 2016 at 14:38
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    $\begingroup$ "Some trillion years" seems a bit long, in fact so long that our galaxy is probably "dying" or "dead" by then. Just a few tens of millions of years should be plenty enough to colonize the entire galaxy even with sub-lightspeed, and have resources to do planetary scale expetiments. $\endgroup$
    – hyde
    Commented Nov 8, 2016 at 21:28
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    $\begingroup$ What @hyde said. "Some trillion years" is at least three, maybe four, orders of magnitude too much time. Dealing with sense of scale in space on Worldbuilding Meta. $\endgroup$
    – user
    Commented Nov 9, 2016 at 8:49
  • $\begingroup$ 1 Billion years, that's the estimative it toke the first time. Remember it tries to recreact earth early enviroment $\endgroup$
    – jean
    Commented Nov 9, 2016 at 15:43

6 Answers 6


This question cannot be answered as we simply do not know.

We have a sample set of 1 - us.

Based on that sample set the answer is 4.5 billion years, however we have no idea what factors would make that a much shorter or much longer time.

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    $\begingroup$ Agreed - there is no real way of mapping how the various natural events over the lifetime of the earth affected the development of Intelligent Life. You could argue that, were it not for the regular Extinction Events, intelligence might have evolved sooner, but equally you could argue that mammals wouldn't have had the opportunity to thrive and become intelligent of natural disasters hadn't wiped out the Dinosaurs. $\endgroup$ Commented Nov 8, 2016 at 14:10
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    $\begingroup$ Actually it is 4.2 billion years. Reason why is left as an exercise to the reader. $\endgroup$ Commented Nov 8, 2016 at 17:40
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    $\begingroup$ @Mindwin Could you please clarify? Google suggests the earth is 4.543 billion years old, and life started 3.8 billion years ago. What does 4.2 represent? $\endgroup$
    – Tim
    Commented Nov 8, 2016 at 17:59
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    $\begingroup$ We are in a context of a question about life, the universe (and probably everything); that is the right answer. $\endgroup$ Commented Nov 8, 2016 at 18:07
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    $\begingroup$ @IStanley Extinction events might have helped the development of intelligent life. Keep in mind: evolution is not guided towards intelligent life. Dinosaurs were quite well adapted to their environment, they were relatively dumb, but their existence probably prevented other species from becoming intelligent because to become intelligent you must put more energy in the brain which means a weaker body, which means dinosaurs chase you more easily. Extinction events wiped out some "dead branches" which probably wouldn't ever reach human intelligence and allowed some kind of re-set. $\endgroup$
    – Bakuriu
    Commented Nov 9, 2016 at 8:24

Estimating from the original experiment, we can statistically determine the likelihood of a molecule of a given size being formed.

Over the course of one week, the just over 50 g of starting material yielded (extremely roughly) 2 g glycine (molecular size of 10 atoms), 2 g α-alanine (12 atoms) and less than 1 g aspartic acid (16 atoms), and a near negligible amount of others, none detected were larger than 18 atoms. Measureing only products, this gives us an average molecular size of 12 atoms with a standard deviation of 2.44, matching fairly tightly to a normal distribution (a standard bell curve).

The smallest known truly self-replicating evolution-capable molecule is the ribosome, composed of 90,000 atoms. That is 37,000 standard deviations from the mean, so we could expect something the size of a ribosome to form once in 2.958×10297,274,578 molecules produced by the experiment.

A planet the size of Earth contains roughly 1.3×1050 atoms, and if we assume 1% are converted per week (by weight), as the data suggests, and are removed and replaced (for convenience) it would take 2×10316,227,766 years to produce the amount of molecules needed.

TLDR: If effected by no processes other than those described by the Miller-Urey experiment, it would take billions of billions of times longer than the universe will exist to generate anything like life, let alone intelligent life in a planet scale version of this experiment.

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    $\begingroup$ To the anonomous editor: it would be very much preferred not to use gratuatous TeX formatting on every single number in the post. The only formatting needed here is the superscripts at the end and that can be done without TeX, using <sup> tag. $\endgroup$
    – JDługosz
    Commented Nov 9, 2016 at 7:45
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    $\begingroup$ Inline TeX does not work great on every browser/platform. And it substantially slows page rendering on a tablet. $\endgroup$
    – JDługosz
    Commented Nov 9, 2016 at 7:46
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    $\begingroup$ This honestly, is one of the larger issues non-evolutionists have with evolution. There currently isn't a great explanation on how life started. Miller-Urey got a first step, but there's apparently more required. Assuming of course, that's how it happened. $\endgroup$
    – DonyorM
    Commented Nov 9, 2016 at 11:00
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    $\begingroup$ The ribosome is the simplest self-replicator known. There may be much simple life forms available on a planet without competitors. $\endgroup$ Commented Nov 9, 2016 at 11:24
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    $\begingroup$ "and are removed and replaced" The problem is removing them may have very large effects on the time - there is no chance of the larger molecules combining with each other. $\endgroup$
    – LeBleu
    Commented Nov 9, 2016 at 19:59

The thing is, the Miller-Urey experiment was never intended to recreate life, or anything close to life. It was very much a first step, showing that in theory, it was possible to create biological precursor chemicals from simple precursors that could have been available in an early earth's atmosphere. Since then, we've found dozens of other paths that can create those chemicals, and even found them on comets and other objects in space. Starting with a Miller-Urey experiment simply makes no sense.

Now, if the question is "If future god-like humans set up a planet with appropriate conditions for organic chemistry to begin, how long before you would get intelligent life?", we still can't give you a good answer, but at least the question makes more sense.

Judging by our sample size of 1, we can make some vague generalisations to get an approximation of an answer. First, we can assume that intelligent life would need to be multicellular. Without a multicellular structure, life is too small to build specialized organs like brains. On earth, it seems that the step from unicellular life to complex multicellular life was the most difficult step to take - it appears that simple multicellularity has evolved 40+ times, whereas complex multicellularity only seems to have emerged six times (animals, fungi, plants, and three kinds of algae), and only one of those lines is suitable for the development of intelligence.

The best evidence we currently have suggests that it took around 4 billion years for animals to evolve. After that, the first land life emerged relatively quickly, about 500 million years ago. From there, the emergence of intelligence is just a matter of evolution and some selective pressure tending towards big brains. On earth, that took at most 500 million years - we don't know if intelligence emerged at any time before us.

But this is just a sample size of 1, so any conclusions we can come to are extremely tentative and black-swannish. We don't know if earth was unusually well suited for intelligent life, or unusually hostile for intelligent life. We don't know if intelligence emerged many times on this earth before being wiped out by mass extinctions, or if we're unique in all the history of the world. (We can be reasonably sure that we're the first industrial civilization, for a variety of reasons).


The true situation in the primordial Earth (we now know) is distinct from the situation in the noted experiment, and far more complicated. If the experiment were carefully controlled to prevent other things, it would never progress to life.

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    $\begingroup$ Finally an answer with sense. $\endgroup$ Commented Nov 9, 2016 at 13:25

What we do know is that any theory that predicts that a planet-sized Miller-Urey experiment would produce life in an average time of millions of years or less; any such theory is consistent with reality. Signs of life were found on Earth dating as far back as we have solid rock to check. That's a huge range of possibilities for how long it would take.

From there, it took about 3 billion years to develop multicellular life. From there, it took a few hundred million years to produce hominids. After that, a couple million years and we have humans. From there, tens of thousands of years and we have an industrial revolution. It's been less than two centuries since then.

The biggest variable in this picture is how long it took for multicellular life to form. Once it arrived, it exploded across the planet. We have no idea what the trigger was that caused that development. There's no reason to suspect that event couldn't have happened a billion years earlier or later.

But as far as Miller-Urey is concerned, developing life from no life could have happened instantly or could have taken many millions of years. The one data point we have provides us no ability to distinguish those timescales.


somewhere between 3 billion years and infinity/never. evolution is not goal oriented, so getting intelligent life is more or less random once you have the body conditions that can support it, and getting those conditions also has a largely random aspect.


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