A Long Time Ago...
Approximately 50 million years ago an asteroid, some 10km in diameter slammed into what is now Mexico's Yucatan Peninsula near the town of Chicxulub. The resulting dust cloud destroyed most living things and ended the dinosaurs reign on earth. The evidence for this has been known for some time, with the deposits of Iridium-rich clay found at the boundary of Cretaceous and Tertiary deposits (known as the K/T Boundary) all over the world.
On July 2 1992, Alan R. Hildebrand of the Geological Survey of Canada presented a scientific paper to the General Assembly of the Royal Astronomical Society of Canada entitled "The Cretaceous/Tertiary Boundary Impact". Some of his findings are summarized here.
The K/T boundary layer, sometimes known as the iridium bearing clay layer, has a global distribution and consists of at least two layers of impact material.
A Major Impact on Earth?
Many scientists believe that the enormous impact put enough dust into the upper atmosphere to darken and hence cool the Earth for several years. This was theorized to result in shutting off global photosynthesis, with the resulting collapse of the global food chain. As a result nothing larger than 25 kg survived the boundary.
Iridium is found all over the world in the K/T layer and is not an unknown metal (commodity), however; its ability to be used in a manufacture type environment is unique. The current products that use Iridium are cellular telephones (Motorola), sunglasses (Oakley), and now spark plugs (DENSO). The reason for only a few companies using this precious metal is its difficulty to be manipulated in a cost-effective manner.