Question

How did the earth acquire the heavy metals necessary for civilization?

Large stars that are big and hot enough to fuse simple elements into heavier metals have shorter lifetimes, because they burn out of fuel faster. If they are large enough, the nuclear reactions overcome the stars' gravity and they supernova, spreading their contents all over the galaxy. These particles, including very heavy metals, travel through interstellar space as a solar wind from the power of the explosion. Then, as other stars are forming their rotating solar systems, the stellar wind passes by, sweeping the lighter gasses and dust out of the protoplanetary disk that surrounds the star. Planitessimals form from clumped matter in the disk and condense. The heavy metals and silicates that are in these winds get trapped by the system and collide into the planitessimals. The lighter, more volatile elements such as hydrogen get pushed outward, and as a result, a planet containing heavy metals emerges. These elements also come from the Big Bang, which created an original "cosmic abundance" of elements such as the heavy metals necessary for structure and life on Earth: iron, magnesium, and silicon. The University of Colorado does much research in this area, so check out its web site at http://argyre.colorado.edu/life/CAB.html Also check out the Origins Program at another Member Institute, the Jet Propulsion Laboratory: http://origins.jpl.nasa.gov/
March 11, 2002