Stellar nucleosynthesis is responsible for creating the elements heavier than lithium (except perhaps some of the heaviest that might result from neutron star collisions).

Eventually, the star goes nova and disperses all these heavier atoms into the vastness of space in every direction.

Later, thanks to encounters with existing clouds of interstellar gas and dust and the patient work of gravity, the nova products will begin to coalesce into new stars and planets, which is how we exist.

So my question is, how do tiny dust particles of dozens of elements sort themselves out so that planets have distinct deposits of minerals rather than being balls made of an undifferentiated mixture of every element?

  • 2
    $\begingroup$ Most of the sorting processes happen on Earth. This might be better in Earth Science $\endgroup$
    – James K
    Oct 29, 2022 at 12:54
  • 1
    $\begingroup$ Sedimentation in protoplanetary disks is definitely A Thing review article so I would say this is on topic for Astronomy $\endgroup$ Oct 29, 2022 at 15:43
  • 1
    $\begingroup$ Needs rewriting to focus on astrophysics rather than Earth science. $\endgroup$
    – ProfRob
    Oct 29, 2022 at 17:28
  • 1
    $\begingroup$ @JamesK This didn't just happen on Earth. All of the terrestrial planet-like objects are highly depleted in hydrogen and helium compared to the solar system as a whole, and all of those objects underwent differentiation. You should undelete your self-deleted answer. $\endgroup$ Oct 30, 2022 at 11:28
  • 1
    $\begingroup$ @david, okay but with reservations. $\endgroup$
    – James K
    Oct 30, 2022 at 12:13

1 Answer 1


Different elements have different chemical and physical properties (and on Earth, different biological properties) As atoms with the same or similar properties tend to move the same way, there is sorting. This happens on all sorts of levels.

Volatile elements, especially light novel gas like Helium or Neon, will get sorted from heavier elements by the action of the solar wind in the early formation of terrestrial planets.

Elements can be classed as siderophile, lithophile, chalcophile, or atmophile. They are sorted when the planet is forming and is largely, or completely molten. The "iron-loving" siderophile elements sink to the core. The "ore-loving" elements are found in the mantle. The "rock-loving" elements are found in the mantle and crust, and the atmophile elements in the atmosphere. Different minerals crystalise at different temperatures, so you get separation of minerals.

Chemical properties further sort the elements, for example chlorine will react preferentially with sodium, and the resulting salt is very soluble, so will tend to migrate to the ocean.

And on Earth, biology plays a major role, for example it moves carbon out of the atmosphere and into the biosphere, and from there, to the crust.

This happens over and over on every scale: volcanos pull chalcophile elements from the mantle, but as they are chemically different from the lithophile elements in the crust, they will tend to group together, forming deposits of ores. These deposits might be formed after several stages of erosion/deposition, in each cycle the sorting repeats, resulting in the ore becoming more refined.

A planet is like a big box of muesli; as you shake it, the nuts and fruit will separate from the oats, as a result of their different properties. An increase in entropy can result in separation, not mixing.

  • $\begingroup$ Hmm, this answer is really all Earth science..... $\endgroup$
    – James K
    Oct 29, 2022 at 12:53

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .