# How elements came to earth

1. ### Aziza

190
we are currently learning about radioactivity and i have become curious of how these heavier elements came to earth in the first place? From what i understand, the lighter elements are formed by fusion in stars, but even so, how could these lighter elements reach us when the stars are so far away? I could see perhaps some of the elements reaching us as dust or something, but how did enough of it reach us to allow for start of life? I mean carbon for example is absolutely essential to life, so we would need extremely large amount of it for the first living cells to begin synthesizing themselves.

Also, according to current model, the early earth was big glob of lava and whatnot, so all of the chemicals must have been mixing around all together, so then why today we have more or less even "deposits" of certain chemicals, like uranium? I mean if in liquid form the earth was all mixed up, then how come when it cooled, it became more ordered in terms of chemical composition?

2. ### Dickfore

The nebula from which the Solar system was created was from a Supernova from a previous generation. All naturally occurring isotopes beyond $^{56}\mathrm{Fe}$ are created that way.

3. ### DaveC426913

16,534
Yup, while a nonzero potion of the Earth's minerals were deposited by meteors, comets and falling space dust, the vast bulk of the Earth coalesced at the same time as the the other planets and the sun from the original collapsing nebula. That original nebula of gas an dust is the remnants of earlier supernovae ejecta.

The reason it isn't all perfectly homogenous is because parts of the Earth cool at different rates, heavier parts sink, lighter parts float so you get sedimentation layers - and then - tectonic activity stirs it all up.

And that's an ubersimplification. The dynamics of a forming and cooling planet are very complex and result in a great degree of heterogeny in materials.

4. ### DrStupid

743
Are sure that is was a single supernova and not a protostellar nebula enriched with metals by many supernovas?

### Staff: Mentor

It is highly unlikely that ALL of the elements came from 1 supernova. The galaxy has been riddled with supernovae since it's initial formation 12+ billion years ago.

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7. ### Naty1

Just heard on tv a few nights ago something even more astonishing: One of the four building blocks of RNA [AGTC] was found just a few years ago in an asteroid or meteor found here on earth....I think it was "G"....

So not only the elements above Fe are here from supernovas, which is correct, but the building blocks for life may have arrived here from elsewhere as well...

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