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I have been looking into the earliest possible time in the universe that a human-like intelligent species could evolve based on the necessary elements being present.

Kepler-444 is one of the oldest solar systems with rocky planets that has been observed. It is 11.2 billion years old and although the planets are too close to its star for life as we know to develop, its existence means that habitable rocky planets could have existed at this period of only 2.6 billion years after the Big Bang.

As we go further back in time the metallicity of stars becomes much lower, so the chances of a solar system forming with all the necessary elements for complicated life will be very unlikely but as we have learned more recently, supernova are only responsible for creating elements up to the heaviness of iron and all the heavier elements are likely creating in neutron star mergers.

This makes me wonder: could neutron star mergers can raise the chances of a solar system existing with the necessary elements for earth-like life at the time of the population III stars when the universe was only hundreds of million years old? Such solar systems might be very rare but are they possible?

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    $\begingroup$ As you ask confirmation of an idea you have already found, better put a reference. And I wonder where you found supernovae do not produce elements heavier than iron. astronomy.com/magazine/ask-astro/2020/12/… And I found another source that states colliding neutron stars could have caused U235 and U238 to exist in Earth's crust, but the old idea (supernovae) is not ruled out there.. world-nuclear.org/information-library/nuclear-fuel-cycle/… $\endgroup$
    – Goodies
    Apr 2 at 12:44
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    $\begingroup$ Some heavier elements are only produced in a kilonova but do you need these elements to form complex organic molecules? $\endgroup$
    – user6760
    Apr 2 at 13:32
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    $\begingroup$ @Jarred Jones The problem with your question is that once the first lifeforms emerge there should still be billions of years of evolutin before the first multi celled lifeforms evolve, just as on Earth. If you want intelligent life to evolve on your early planets that should be billions of years after those planets form. Of course some planets might evolve advanced life many times faster than other planets, but they would be comparatively rare compared to the planets which evolve complex life at the same rate as Earth did. $\endgroup$ Apr 2 at 18:19
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    $\begingroup$ @M.A.Golding I know, that is why I said "based on the necessary elements being present". I didn't want to mention the time for them to evolve or how rare that would be as answers may spend time on that. I am thinking about how long the solar system will take to form and how long it will take for life to evolve and what the stages will be. I am also thinking about time for them colonize space and the distances as the universe expands. $\endgroup$
    – user94655
    Apr 2 at 18:54
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    $\begingroup$ @M.A.Golding We only have one data point to go on there. We don't know if Earth took an "average" amount of time to evolve complex life from early life, and therefore should expect other similar histories to be more common than wildly different ones. Maybe complex life on Earth took an extremely long time to get going, by universal standards. Or maybe Earth is already at the 99th percentile for how fast it was, and even fast should be astonishingly rare. We don't even know if complex life is common enough for there to be a meaningful average for how fast it develops. $\endgroup$
    – Ben
    Apr 2 at 23:30

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I'll note that it's a misconception that you can't form elements heavier than iron in normal core collapse supernova. Supernovae certainly allow the r-process to take place, and I believe that historically they were thought to be the dominant r-process mechanism. That assumption is certainly being challenged these days as our understanding of kilonovae improves, but there are still plenty of uncertainties in models of mergers.

Either way, the later stages of fusion in massive stars will produce the really key elements like carbon, oxygen, nitrogen and phosphorus. It would take a few generations for stars to actually be able to undergo this fusion - the first Population III stars won't produce all of the elements you need - but it will happen, and it should happen with the first few hundreds of millions of years after the first stars. The s-process should slightly later, in AGB stars, depending on their lifetimes.

I would bet against neutron star mergers being of any use for any sort of element in your scenario because they typically occur on very long timescales. For example, the Hulse-Taylor binary is expected to merge in $\sim$300 million years, and it's already taken a long time to get to this point. Many known neutron star binaries will not merge within $\sim$10 billion years. Particularly in the early universe, we'd expect these events to be extremely rare. So even if kilonovae are the dominant sources of, for example, r-process elements in the universe today, that would not be the case in the very early time periods you're interested in.

Again, this is subject to plenty of uncertainties, particularly in regard to the dominant mechanisms for producing neutron star mergers at different points in the life of the universe. But I wouldn't bet on them being at all significant early in the universe.

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This chart gives, per element, which is its place of formation in the universe

enter image description here

Life as we know is based on carbon, oxygen, nitrogen, hydrogen and depends on iron, magnesium, potassium, sulfur, calcium and some other elements.

Out of my memory none of the elements produced in merging neutron stars in essential for life. Therefore having a large amount of neutron star merging event won't increase the chances of early arising of complex life.

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  • $\begingroup$ That is a helpful diagram but there are a few heavy elements according to this list which fall into the neutron star merger only category. Such as Thorium, Radium and Radon. azchemistry.com/chemical-elements-human-body $\endgroup$
    – user94655
    Apr 2 at 13:26
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    $\begingroup$ @JarredJones "found in the human body" is a very, very long way from "essential for life". If you can find anything like an enzyme without which an organism could not survive that's built on eg. thorium, I'd be fascinated to see it, but I shan't be holding my breath. $\endgroup$ Apr 2 at 13:50
  • $\begingroup$ L.Dutch and Starfish Prime, so then if we forget about neutron star mergers does this mean earlier generation of stars can produce all necessary elements? Even the first stars? $\endgroup$
    – user94655
    Apr 2 at 13:58
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You cannot use a neutron star merger as a substitute for a supernovae, because every neutron star comes from a supernovae.

If you want complex life in the early universe don't ask yourself "how do I get mergers that early?" Instead ask "how do I get supernovae that early?"

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  • $\begingroup$ I did not know (until comments and answers pointed it out) that all necessary elements could be formed in supernova and especially from the early stars. I also assumed that mergers of neutron stars were frequent in the past due to the high star production but it has been pointed out that they were not. $\endgroup$
    – user94655
    Apr 3 at 11:46
  • $\begingroup$ @JarredJones So there is no problem at all. Sounds like the best outcome for a WB question! $\endgroup$
    – Daron
    Apr 3 at 12:35
  • $\begingroup$ Indeed, the knowledge for me and earlier time in the universe for the elements makes for a better worldbuilding outcome. $\endgroup$
    – user94655
    Apr 3 at 13:13
  • $\begingroup$ The reason why I commented late is because I did not think the answer added to the previous answers, normally I would let it be but better to point it out than have it repeated. $\endgroup$
    – user94655
    Apr 3 at 13:50
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You don't need neutron stars for life.

you don't need anything made in a kilonova to make life, life is made of the most common elements in the universe. All made in simple supernova or even more common phenomenon. The few rare heavy element that does very rarely occur in some life are not essential but opportunistic.

You have to look hard to even find anything in row five of periodic table in life, mostly iodine, molybdenum and tungsten, all of them are incorporated later in evolution and only in very tiny amounts, so there is no reason they would have to be used. AND they also can form in low mass stars.

Your planet will notice since it will mean it is much harder to have plate Tectonics without heavy radioactive elements but life will not notice.

You do need supernova, Oxygen is one of the four absolutely, without a doubt, essential elements for life and oxygen only comes from exploding stars. the list of undeniably necessary elements for complex life are what makes up all macronutrients.

C H O N P K Ca S Mg

You must have these elements in abundance, doubly so for the bolded.

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