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In thinking about exclusion options for where its not worth to look for habitable planets, the past came to my mind.

Right at the beginning of the universe, there was no possibility for (carbon based) life supporting planets to form, simply because there was not enough material to do so.

Population III stars burnt out within millions of years to leave some of these elements, but was it enough to form planets? I have some problem getting things into perspective, considering that

  • there are so many processes that produce different kinds and amounts of isotopes
  • these isotopes are spread out in various different ways (and thus also different concentrations from how they were created) throughout the interstellar medium
  • it takes probably a lot of time to gravitationally condense enough metals into a planet once it was spewed out from e.g. a super nova
  • the majority of stars are smaller so it would probably take a clustering of heavier stars to provide the conditions earlier in the universe.

I would consider a similar distribution of metals like in earth as sufficient for life, and would concentrate only on those found in DNA (N,H,C,P,O), fats (C,H,O) and proteins (C,O,H,N) as well as most of the essential minerals (Ca,Cl,K,Na,Mg,P,S) and maybe at least a bunch of (possibly essential) trace elements (Co,Fe,I,Cu,Mn,Mo,Se,Zn,As,B,Cr,F,Rb,Te,V,Sn,Ni).

So what is the best approximation that we can currently give on when these elements were abundant enough to condense into earth like rocks with earth like elemental distribution?

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  • $\begingroup$ There is some (calculational) evidence that early Pop III stars could have been in the neighborhood of $100-1000\:M_{\odot}$. Obviously, given that stellar lifetime is inversely proportional to mass, these stars would have created heavy elements and died extremely quickly such that it is possible the early universe was seeded quite quickly with heavy elements. What's more, if you're considering elements heavier than Iron, you primarily need to be concerned with radioactive element production such as Uranium. These can decay into the myriad of others over time. $\endgroup$ – zephyr Aug 30 '16 at 19:56
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You can get relatively high metallicity rather quickly in parts of the early universe -- especially some globular clusters and the centers of massive galaxies -- because star formation rates in those places were very high, which means lots of massive stars and several rounds of "massive stars form, go supernova and seed surrounding gas with metals, new massive stars form out of enriched gas" -- the timescale from formation to supernova can be as short as 2 million years for really massive stars.

So how high a metallicity do you need to form planets, and how early did (parts of) the universe get there?

  • One the one hand, we know of a star with a metallicity (iron abundance) only a quarter of the Sun's ([Fe/H] = -0.63) with a Neptune-mass planet, and Kepler has found roughly Earth-sized planets around stars almost as metal-poor. So you don't need very high metallicities to form planets.

  • On the other hand, there is evidence of gas around quasars enriched to above solar metallicity by redshifts of 6 to 7 (about 800 million years after the Big Bang). There are also rather old stars in our galaxy with high metallicities: for example, this paper estimates that the stars in the globular cluster NGC 6258 are 10-12 billion years old with near-solar metallicity.

So the short answer is that you could have planets forming within the first 1-2 billion years after the Big Bang, and quite possibly within a few hundred million years after the first stars formed. Because the metals would mostly be from core-collapse supernova (as opposed to the iron-dominated products of Type Ia supernovae), there would be an excess of so-called "alpha elements" -- particularly oxygen, magnesium, neon, silicon, sulfer, argon, and calcium -- relative to iron; I don't think you'd have to worry about missing too many life-critical elements.

These planets would not all be very good places for life, however, because they would be in dense regions with lots of stars and lots of star formation, meaning lots of supernovae going off nearby, and possibly an active quasar as well if we're talking about a galaxy center.

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