What's 'earth'?

[slimfandango]

What elements on planet earth are from its formation and what has got blown here only from elsewhere? I was thinking gold, maybe, but somehow got thinking of elements in the human body?

[rja211077]

nothing has got 'blown' here from elsewhere. certain elements - the radioactive ones towards the upper end of the periodic table - have only ever existed for short periods after being artificially created in labs, but the rest are from the earth's formation.

[jake-the-peg]

I think you may be thinking about the formation of the elements in stars.

Pretty much only Hydrogen and Helium were created in the big bang - these elements formed the first stars - (we call these population 2 stars because they were found later) When the hydrogen in a star is all used up it start making other elements in different fusion reactions. This continues until iron is reached. The reaction to make iron is endothermic (it consumes more energy than it liberates) at this point your star collapses, if your star is large enough at this point it will become a supernova and explode in the most unbelievable event creating temperatures and pressures high enough to create every othre element.

The gold connections in the computer you are using now, the copper in the wires and the iron in your blood was created in a supernova before our solar system was formed.

You are truely stardust  

[brachiopod]

Sh1t !!! B*****cks !!! F***** Arrrghhhhh ***** C**** !!!

Just typed out a whole reply to this but was 2208 characters and too long to post. So whilst I was figuring which 208 characters to cut, I accidentally clicked on the edge of one of those white, borderless f******* adverts on the side, thinking it was a bit of white space, and lost my entire answer. ***** !!

[brachiopod]

Right, had a fag and calmed down now....

Much of what I was going to say agrees with rja and jake.

That apart from the man-made elements created in nuclear reactors and particle accelerators, all other elements were 'cooked up' in stellar processes. (good explanation, jake).

The only proviso, is with isotopes of elements with a short half-life. For example Thorium-230 is a decay product of Uranium-234, and has a half-life of 75 years. This means that any Thorium-230 you find on Earth today would not have existed as that element at the Earth's creation, but would be a recent decay product.

To clarify, a product of radioactive deacy would be a new atom of an existing element, although it would be made up from some of the protons and neutrons of its ultimate parent element, which would have existed at the Earth's formation.

Finally, neither meteorites, nor the thousands of tonnes of cosmic dust that land on the Earth each year introduce any element that does not already exist here on Earth - though of course, they do add mass, or in other words, new atoms of an existing element.

(I put it so much better the first time.....)

[slimfandango]

Crikey, awesome answers. I actually felt ****ed off for brachiopod getting ****ed off, so many expletives!

So I'm almost at a full answer. Our solar system did not "create" all the elements in the planets. So there are things like iron and gold that are here now, that could only have come from supernovae. When the dust and gas was collecting together to create the solar system, did that contain gold and iron, or was gold and iron blown at us from supernovae at/during/after earth's formation?

thanks guys.

[jake-the-peg]

The dust cloud that condensed to form out whole solar sytem contained the mix of elements that we see today on earth.

Most of the stars you see in galaxies today are like this, they are if you like second generation stars - we call them population I stars - their spectra show the presence of the full mixture of elements.

The older first generation stars (population 2) are typically seen in small globula clusters orbiting main galaxies they typically only show hydrogen and helium in their specta. Some esimates put stars in these clusters at 15-20 billion years.

They are some of the oldest things we know of.