by Dr. Joe Andrade, Professor of Engineering, The University of Utah & Science Advisor, the Leonardo
I’ve always been fascinated by the fact that basically the entire Periodic Table is in the ocean and in us
. In the Channel 9 (KUEN) telecourse, Science without Walls (Bioengineering 1510), I have a program/video titled: YOUR Personal Periodic Table, where we show that some 60 different elements are now easily detected in human tissues. They are not contaminants – they’ve been there from the very beginning of life on Earth. You are a walking, breathing Periodic Table! (thanks to ARUP Labs for the analytical part of this program).
With National Radon Action month every January, with all the interest in depleted Uranium, and with my personal interest in finding ways to get general people interested in matter and the Periodic Table – and because of my ignorance in all things Astronomy – I’ve had to do some homework.
Why do we have so many different elements on Earth if the whole Universe is mainly Hydrogen and Helium? How does Nature ‘make’ elements like Uranium? Why is Uranium actually fairly common on Earth?
After doing some homework, and especially reading: The Supernova Story, Laurence A Marschall, 1988, I now know something:
- supernovae scatter the elements of life among the stars
- the Sun ‘burns’ Hydrogen via fusion, producing Helium
- in very hot cores, Helium atoms can fuse to become Carbon
(Helium ‘burning’)
- carbon atoms can fuse to produce Neon, Magnesium,
etc.
- in very large stars, heavier and heavier elements can be
made by fusion, up to the very stable Iron 56.
Marschall says clearly: ‘The star develops a structure like an onion, with the heaviest elements at the center and the unburned lighter elements at the surface.’ Of course, this isn’t the ‘burning’ you and I know – these are nuclear fusion processes.
But the Periodic Table doesn’t stop at Iron 56 – it continues on to Uranium 92. So how are Elements 57 to 92 made? It’s apparently all due to Gravity. The dense iron core of a large massive star gets compressed by gravity, becoming a type of neutron star. The ultra-dense core sucks in the matter around it and then explodes out into space as sort of a shock wave. But there is also a huge neutron flux which converts, actually in a very short time, some of the elements originally synthesized (‘burned’) in fusion reactions into the high mass, high number elements of the Periodic Table – all the way out to Uranium. The creation of the elements beyond Iron are largely due to neutron collision and capture processes – a hot, nuclear alchemy!
Marschall says, so beautifully: “A supernova is an act of creation. Our familiar world is built from the debris of stars.”
The great science communicator (also a great scientist), Carl Sagan, perhaps said it best: We are all star-stuff. See him say it on YouTube: http://www.youtube.com/watch?v=iE9dEAx5Sgw
Our little Earth has ‘inherited’ its entire composition from Star Stuff – some 5 Billion years ago when the planet first coalesced from the gases and debris of space. And star-stuff is still being made – by high energy cosmic rays hitting atoms in the upper atmosphere. Nuclear alchemy is alive and well, albeit on a very small scale.
But for now, when you see (carefully!) the Sun, appreciate that it is a Hydrogen and Helium fueled nuclear fusion reactor, a safe 100 million miles away – making star stuff and making the incredible solar energy which fuels all life on our little green and blue planet. No wonder the ancients worshipped the Sun.
Enjoy and protect Planet Earth!
Joe.andrade@utah.edu
June 20, 2010
