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Name: Kevin
Status: educator
Grade: 6-8
Location: Outside U.S.
Country: USA
Date: Fall 2012


Question:
I know that all of the elements heavier than iron were formed in supernovae. When the star goes nova, wouldn not the atoms of these elements be scattered randomly across the cosmos? If so, how is it that they are concentrated enough in various places on Earth so as to make it possible to mine metals?


Replies:
Kevin,

One of the contributing factors is how solar systems form. If solar system objects form from gases and random agglomeration of these gas particles, then more massive particles are likely to concentrate first. They would have a stronger gravitational pull which will only get stronger as they accumulate more of the same heavy elements. Lighter elements and gas molecules are likely to be the last to be accumulated.

Another contributing factor is the geological history of planets. If the planet has a lot of volcanic activity, then this will melt much of the planet and since substances tend to crystallize in such a way that excludes other substances (other substances do not fit properly into the crystalline pattern of the fusing substance), then the repeated melting and roiling of the planet body is going to make specific substances melt together and concentrate.

For gaseous planets that do not have volcanic activity, concentration is a function of mass, kinetic energy, and where these substances fall within the gravity well of the planet.

Greg (Roberto Gregorius) Canisius College


Hi Kevin,

The atoms are randomly displaced initially, but atoms quickly respond to cohesion forces to form particles. The particles are not necessarily scattered randomly over time. Think of a form of chromatography or centrifugation, heavy elements will tend to migrate at one rate while other lighter particles may move differently. Or think of a heavy projectile flying a shorter distance than a lighter one.

All of the particles will be attracted to each other to form larger rocks and ice-rock mixtures. Some of those will be enriched with heavy elements, some will not.

As Earth is bombarded with particulates and meteors, they may form an enriched vein. The Cretaceous - Paleogene event (K-T in older texts) is a case in point: iridium is greatly enriched in the layer formed as a result of the meteor impact.

Hope this helps! Peter E. Hughes, Ph.D. Milford, NH


Some of the heavy elements from supernovae enrich molecular clouds which collapse to form solar systems. This leads to higher concentration of heavies in places where planets form.

Joseph P. Bernstein



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