# Which theory is stronger, that iron came from outside or was formed within earth?

Where is the current body of science learning towards, that iron came from meteor or it was somehow formed on earth?

• Do you mean the element itself (in which case the answers below are sufficient), or deposits of ore or even metallic iron that people could use? Jan 23, 2015 at 19:28
• Or the Earth's core? (I assume not, but...) Feb 4, 2015 at 6:08
• Iron came 'down' from above: bit.ly/1I3vjDs Dec 14, 2015 at 10:28

The only elements that were formed on Earth are those produced by radioactive decay. There are four natural decay chains that start with transuranic elements and none terminate in iron; neither do the decay chains that are artificial or those that result from cosmic radiation. So all of our iron is from the Earth's formation or meteor impacts since then.

• historically speaking, how far back could this theory be traced? Aug 5, 2014 at 21:02
• To 1946 when Fred Hoyle described the nucleosynthesis of iron, meaning that it occurred in stars that predate our solar system. Aug 6, 2014 at 2:34
• if this was written say over 1000 years ago would that be unbelievable or you could say it was a good educated guess? Aug 7, 2014 at 18:30
• @JackTwain: so? Just because a question is triggered by a theological discussion does not mean that the answer has to be theological. This is a science site. That page has nothing to do with science. Feb 19, 2015 at 1:42
• Minor disagreement, there are elements on Earth that are formed via fusion and particle bombardment, but granted, these are in small quantities. As there is enough of them produced and put into weapons of mass destruction to kill man many times over, it is not insignificant though.
– dlb
Sep 30, 2016 at 23:12

All the material that eventually formed our solar system is essentially recycled star dust. All iron on Earth was produced by large stars that existed before our Sun formed: the iron was created during nuclear fusion and later released when the parent star(s) exploded, presumably supernova. After our solar nebula had formed and material had been gravitationally compacted, dense elements like iron did not get far from the center of the nebula before "precipitating" out into planets and meteors. Thus the inner solar system has a high abundance of iron. This is in contrast to low-density elements/molecules that were in general able to escape the center of the nebula and make it pretty far before being pulled into a large mass. So we have high iron planets and meteors close to the sun (relatively speaking), and very little iron in the "gas giants" part of the solar system. I would consider this to be material that is "already there" but certainly some iron has been added by meteors.

Somewhat more from volcanic activity than meteor impacts, but both are important.

The Earth has an iron-nickel ($\ce{Fe}$-$\ce{Ni}$) core that originates from Earth's formation out of the collision of planetesimals which themselves contained iron, rock and ice. The Earth was very hot at that time, and the iron along with some siderophilic elements sunk to the center to form the core. Relatively little of that iron is in the crust. It is mostly sequestered in the core (pages 326, 327).

• The first iron used by humans was meteoric. Nov 26, 2016 at 16:32

I believe the element iron (Fe) is formed by stellar nucleosynthesis.

# stellar nucleosynthesis:

it's a process of continuous fusion of the star element to reach heavier and heavier elements. starting from hydrogen (H) till iron (Fe) (the heaviest element the process could reach).

Each 2 atoms of light elements fuse together to form heavier element atom.

For example 2 hydrogen atoms (H --> 1 proton) fuse to form helium (He --> 2 protons).

• Could you explain a little more what stellar nucleosynthesis is in your answer? Thanks! Aug 12, 2014 at 23:45

So (naturally occurring) elements on earth can only come to be here in three ways.

Either they are formed here via radioactive decay.
They came via meteor.