The Periodic Table, is one of the truly iconic scientific images ^[1], albeit one with a variety of forms. In the picture above, the normal Periodic Table has been repurposed in a novel manner to illuminate a different field of scientific enquiry. This version was created by Professor Jennifer Johnson (@jajohnson51) of The Ohio State University and the Sloan Digital Sky Survey (SDSS). It comes from an article on the SDSS blog entitled Origin of the Elements in the Solar System; I’d recommend reading the original post.
 
 
The historical perspective

A modern rendering of the Periodic Table appears above. It probably is superfluous to mention, but the Periodic Table is a visualisation of an underlying principle about elements; that they fall into families with similar properties and that – if appropriately arranged – patterns emerge with family members appearing at regular intervals. Thus the Alkali Metals ^[2], all of which share many important characteristics, form a column on the left-hand extremity of the above Table; the Noble Gases ^[3] form a column on the far right; and, in between, other families form further columns.

Given that the underlying principle driving the organisation of the Periodic Table is essentially a numeric one, we can readily see that it is not just a visualisation, but a data visualisation. This means that Professor Johnson and her colleagues are using an existing data visualisation to convey new information, a valuable technique to have in your arsenal.

One of the original forms of the Periodic Table appears above, alongside its inventor, Dmitri Mendeleev.

As with most things in science ^[4], my beguilingly straightforward formulation of “its inventor” is rather less clear-cut in practice. Mendeleev’s work – like Newton’s before him – rested “on the shoulders of giants” ^[5]. However, as with many areas of scientific endeavour, the chain of contributions winds its way back a long way and specifically to one of the greatest exponents of the scientific method ^[6], Antoine Lavoisier. The later Law of Triads ^[7], was another significant step along the path and – to mix a metaphor – many other scientists provided pieces of the jigsaw puzzle that Mendeleev finally assembled. Indeed around the same time as Mendeleev published his ideas ^[8], so did the much less celebrated Julius Meyer; Meyer and Mendeleev’s work shared several characteristics.

The epithet of inventor attached to Mendeleev for two main reasons: his leaving of gaps in his table, pointing the way to as yet undiscovered elements; and his ordering of table entries according to family behaviour rather than atomic mass ^[9]. None of this is to take away from Mendeleev’s seminal work, it is wholly appropriate that his name will always be linked with his most famous insight. Instead it is my intention is to demonstrate that the the course of true science never did run smooth ^[10].
 
 
The Johnson perspective

Since its creation – and during its many reformulations – the Periodic Table has acted as a pointer for many areas of scientific enquiry. Why do elements fall into families in this way? How many elements are there? Is it possible to achieve the Alchemists’ dream and transmute one element into another? However, the question which Professor Johnson’s diagram addresses is another one, Why is there such an abundance of elements and where did they all come from?

The term nucleosynthesis that appears in the title of this article covers processes by which different atoms are formed from either base nucleons (protons and neutrons) or the combination of smaller atoms. It is nucleosynthesis which attempts to answer the question we are now considering. There are different types.

Our current perspective on where everything in the observable Universe came from is of course the Big Bang ^[11]. This rather tidily accounts for the abundance of element 1, Hydrogen, and much of that of element 2, Helium. This is our first type of nucleosynthesis, Big Bang nucleosynthesis. However, it does not explain where all of the heavier elements came from ^[12]. The first part of the answer is from processes of nuclear fusion in stars. The most prevalent form of this is the fusion of Hydrogen to form Helium (accounting for the remaining Helium atoms), but this process continues creating heavier elements, albeit in ever decreasing quantities. This is stellar nucleosynthesis and refers to those elements created in stars during their normal lives.

While readers may be ready to accept the creation of these heavier elements in stars, an obvious question is How come they aren’t in stars any longer? The answer lies in what happens at the end of the life of a star. This is something that depends on a number of factors, but particularly its mass and also whether or not it is associated with another star, e.g. in a binary system.

Broadly speaking, higher mass stars tend to go out with a bang ^[13], lower mass ones with various kinds of whimpers. The exception to the latter is where the low mass star is coupled to another star, arrangements which can also lead to a considerable explosion as well ^[14]. Of whatever type, violent or passive, star deaths create all of the rest of the heavier elements. Supernovae are also responsible for releasing many heavy elements in to interstellar space, and this process is tagged explosive nucleosynthesis.

Into this relatively tidy model of nucleosynthesis intrudes the phenomenon of cosmic ray fission, by which cosmic rays ^[15] impact on heavier elements causing them to split into smaller constituents. We believe that this process is behind most of the Beryllium and Boron in the Universe as well as some of the Lithium. There are obviously other mechanisms at work like radioactive decay, but the vast majority of elements are created either in stars or during the death of stars.

I have elided many of the details of nucleosynthesis here, it is a complicated and evolving field. What Professor Johnson’s graphic achieves is to reflect current academic thinking around which elements are produced by which type of process. The diagram certainly highlights the fact that the genesis of the elements is a complex story. Perhaps less prosaically, it also encapulates Carl Sagan‘s famous aphorism, the one that Professor Johnson quotes at the beginning of her article and which I will use to close mine.

We are made of starstuff.

 Notes

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