Heavy elements

A few weeks ago I was listening to a radio program from the BBC – Home Planet [it is on Radio 4 and is described as "answering listeners' questions about planet Earth and our impact upon it". One question they were addressing was about the formation of heavy elements and how they came to be distributed on Earth as we find them today. The answer was very interesting, but, as is so commonly the case when I acquire some new knowledge, I immediately had more questions ...

The process of making all the naturally occurring elements has taken many billions of years. After the Big Bang, there was a lot of Hydrogen [atomic number 1], quite a lot of Helium [2] and a bit of Lithium [3]. As stars formed, the nuclear fusion process resulted in heavier elements being formed all the way up to Iron [atomic number 26] and [I assume] the other 22 elements in between. Most of the remaining 70 or so naturally occurring elements were formed by the acquisition of neutrons, which are generated in supernovas and red giants.

This led to the periodic table as we see it today, but it opens up another question. All these atoms of different elements are formed in interstellar space. They gradually clump together to form stars and planetary systems. So, why are planets [like Earth] not simply a mixture of atoms of different elements? Why are most elements found as large groups of atoms in the same place? The answer is far from simple. Essentially, over a very long timescale, a variety of processes caused this accretion to take place. There are chemical processes, where atoms of different elements react together. A variety of physical processes – thermal and gravitational for example – affect atoms differently, depending upon their density, melting point etc. The most intriguing processes are biological.

On the radio program, they cited the example of gold [but implied that this may apply to other elements too], which is processed by very unusual microorganisms – extremephiles – which collect gold atoms to form nanoparticles and, in turn, larger agglomerations. This led me to wonder whether this would be an interesting and effective way to search for signs of life on other planets, as such mineral deposits may be easier to detect remotely. So, I emailed the program.

A couple of days ago, the producer of the program contacted me, inviting me to participate in the program [which will be recorded and broadcast next week] by phone to pose my question. All being well, I will get an answer, but I bet it will raise more questions in my mind.

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Posted December 16th, 2010, by

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Commented on 28 December 2010 at 16:54
By Hugh Griffiths

If I was cautious, I’d wait for your broadcast and listen to the answer. Since I’m not, I will offer my opinion: that mineral deposits on earth have almost nothing at all to do with the action of any living creature, past or present, even if little critters can move tiny bits of gold. The main factors of accretion are volcanic (directly or by forming “veins”) or due to water movement (seas, rivers, rain). So, remotely identifying a gold vein on The Forbidden Planet (even with reversed polarity)would not be a direct clue to life existing there. But, perhaps it could be an indirect clue, since the presence of heavier elements near the crust of a planet implies earlier volcanic activity, which might (or might not!) be related to the probability that life formed there in its turbulent past.

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