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We understand that the Hadean Earth was basically a giant ball of magma, constantly bombarded, no atmosphere, and solidified material never accumulated as Earth was too hot at its surface. We know from the magma that eventually crust formed, and oceans began to form from comet/asteroid bombardment, as well as from volcanic degassing.

...However, Hadean Earth formed after tens of millions of years as gas and dust accumulated to form the planet, but what even is meant by "gas and dust"? When I think of those terms I think of our atmosphere and smog, and dust that would be in the corner of the house. How can it account for all the elements that occur naturally on Earth? It seems as if Earth was created from something that would have no grounds creating Earth. Is a certain temperature implied when "gas and dust" is stated? The dust in the corner of the house can not become magma.

I know my hypothesizing is absurd, but I am doing that on purpose: what is even meant by "gas and dust"? What should be invoked in my mind, since mundane examples are not sufficient?

Edit: I was led to this question through studying Geologic Time and its eras; if this would better fit in another stack exchange like astronomy, sorry for confusion.

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  • $\begingroup$ look up protostars and nebula. planets ore made of the same gas and dust that form stars. $\endgroup$
    – John
    Oct 9, 2023 at 1:58
  • $\begingroup$ I'd say this already has an answer here, at least for the dusty part: astronomy.stackexchange.com/questions/20058/… "Gas" is the primordial (speak: created in the Big Bang) mix of Hydrogen and Helium, enriched with heavier elements from stars over time. Heavy elements then make tiny rocks, i.e. "dust". This mix floats through the galaxy until it becomes cold enough (typically a few 10 Kelvin) to collapse under its own gravity and form stars and planets. How exactly then planets form from this, is an entire science in itself. $\endgroup$ Oct 9, 2023 at 9:23
  • $\begingroup$ I see there is no easy answer. I will leave this open for a bit to see if others can provide a convenient answer. If not I will link to that post. $\endgroup$
    – BigRigz
    Oct 9, 2023 at 14:06

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Very simply. No disrespect, but this is the type of explanation aimed at a young elementary/primary school child.

It starts with hydrogen, helium and lithium . They've been around since the Big Bang. Quantum fluctuations created random zones of differing density material within the early universe. This resulted in some hydrogen collapsing under gravity to form stars. When enough hydrogen was collected, the interior of the stars became very hot and started to fuse hydrogen into different elements. First to be created within the stars, under stellar nucleosynthesis, also known as stellar nuclear fusion, was more helium. As hydrogen became depleted within the star, the heavier elements began to be created under nuclear fusion.

Within stars similar to the Sun, this process ends with the formation of iron, shortly before the star sheds its outer layers explodes; larger stars explode as supernovae. The formation of elements heavier (see the periodic table of elements) than iron results from an alternate process, such as merging neutron stars, which I'll let you to investigate - I'm keeping things as simple as possible.

As the stars explode during a supernova event they disperse the elements they made (He, B, C, O, N, F, Ne, Na, Mg, Al, Si, P, S, Cl Ar, K, Ca, ... Fe) into the nearby cosmos. From this clouds of gas, or gases (oxygen and nitrogen, etc.). The metallic elements are the precursors of cosmic dust. These coalesce under gravity to form larger grains, which in turn coalesce under gravity to form larger particles. Eventually rocks are formed, similar to what is found in the asteroid belt.

Either via the influence of gravity or motion induced collisions, such materials start to coalesce further to form planets, or the cores or planets that later become gas giants.

Each collision produces heat. This along with the heat from decaying nuclear isotopes makes the planets hot enough to become molten. Again, under gravity the heavier elements coalesce towards the center of the planet. The heat and the molten nature of the planet results in the formation of various compounds. As the outer parts of the planet cools solid crystals precipitate out of the molten mass to form solid rock that creates the crust of the planet.

Due to the molten nature of some of the rock, as the planet cools, volcanic activity continues, bring fresher molten material to the surface of the planet. It also release volcanic gases, such as carbon dioxide, to form the initial atmosphere of the planet (see Venus, Earth and Mars).

While all this is going on, the planet will be bombarded by asteroids and comets which bring additional material to the surface of the planet, such as heavy metals and water. This essentially is the Hadean Earth.

Later if life forms, such a cyanobacteria and conditions are favorable, carbon dioxide from the atmosphere will be consumed and oxygen, created by the bacteria, will accumulate in the atmosphere. Having a protective planetary magnetic field helps with retention of the planetary atmosphere.

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  • $\begingroup$ This is OK, but the Sun is too small to create iron (except maybe ridiculously far in the future) or explode in a supernova. A star has to be much bigger than the Sun to do that. $\endgroup$
    – Spencer
    Oct 10, 2023 at 12:30
  • $\begingroup$ +1, reasonable answer, but as the previous comment said, the sun is not going to explode, it will turn into an AGB star. AGB stars are the main source of enriching the galaxy/interstellar medium with heavy elements via strong stellar winds, not supernovae. $\endgroup$ Oct 10, 2023 at 13:30
  • $\begingroup$ Oh this is good. Thank you. I never had such an explanation in primary school nor would I have cared, if I were to be honest, but my intellectual sanity is not as it used to be. :,) $\endgroup$
    – BigRigz
    Oct 11, 2023 at 3:18

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