The production of large nuclei – where did Earth’s elements come from?

Before a star goes into supernova it would have made elements up to and including iron, but the violence of the explosion itself makes nuclei with more protons per nucleus than iron. Between the two ways to fuse heavier nuclei from lighter ones, supernova explosions have made essentially all the nuclei other than hydrogen and helium (though much of the iron stays behind in the collapse core). We have seen that evolving stars can fuse nuclei up to iron, number 26 in the list of elements that starts with hydrogen and helium. If this were the full story we would have no explanation of sixty-six naturally occurring additional elements – those whose nuclei contain anywhere from twenty-seven protons per nucleus (cobalt) through to ninety-two protons per nucleus (uranium). The list of these sixty-six elements includes such important nuclei as copper, silver, iridium, gold, mercury, and lead - as well as rare elements such as dysprosium, ytterbium and hafnium. We now know where the elements with a large number of protons came from; the first fraction of a second of a supernova explosion!

When we look at the Universe as a whole, we find that all of the ‘high number’ elements are extremely rare – hydrogen and helium account for at least 99% of all the mass in the cosmos. The elements with three to twenty-six protons per nucleus (including carbon, nitrogen, oxygen, silicon, magnesium, aluminium, titanium, chromium, and iron) have a total abundance of less than 1% of the mass in hydrogen and helium nuclei. But the total abundance of all the high number nuclei (those with atomic numbers exceeding twenty-six) does not reach one-thousandth of the mass of elements three through to twenty-six! When you look for these high number elements (e.g. silver, mercury, uranium) you are looking for products of rare moments in the Universe, the moments after the explosion of a star.

When the Earth formed, close to our parent star, the warmth of the sun evaporated almost all the hydrogen and helium in our vicinity. As a result of the sun’s warmth, the Earth contains almost none of the two most abundant elements in the Universe. But the remaining elements were sufficiently heavy to avoid evaporation, and their abundances are much the same as we find in stars; oxygen, carbon and nitrogen predominately; silicon, magnesium, aluminium, sulphur, calcium, and iron and nickel appears only in trace amounts. This isn’t the case with everything, as lead, which we don’t think of as very rare, has an abundance of iron’s by a factor of half a million, gold only one tenth of this, and uranium has one tenth the abundance of gold (so very rare!)

When we seek to mine any of the elements heavier than iron (nickel is typically made in small amounts with the fusion of nuclei into iron - but we will exclude this to avoid confusion) we are searching for the remnants of rare moments, the sudden shocks that begun the explosion of supernovae. From these brief outbursts we must pry loose the elements we depend on for their special physical and chemical properties. The properties arise from the nuclear structure of elements that were assembled during tiny fractions of a second, close to a newly collapse neutron star, and then blasted into space through the same furious process that made them, a supernova explosion.

Some of these elements happened to occupy the regions of an interstellar cloud that later become the sun and its planets. And of the elements that made our planet, tiny fractions have temporarily become parts of our bodies. Every atom of oxygen, carbon, iron and the calcium in your bones was created in the core of a star. These nuclei not only connect with the stars and their history; they offer living proof that we would not be here without the stars that exploded to make the elements, which in turn, make us!

Source:https://www.facebook.com/photo.php?fbid=352241721528910&set=a.313338668752549.73826.313312622088487&type=1