Parts of the teeth include: 1  Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of calcium phosphate, a rock-hard mineral. 2  Dentine: A layer underlying the enamel. Dentine is made of living cells, which secrete a hard mineral substance.  Pulp: The softer, living inner structure of teeth.
Though they vary significantly, transportation costs accounted for 40% of the average overall cost of coal delivered at electric power plants in 2010. On average, nominal U.S. rail rates for shipping coal grew from $11.83 to $17.25 per short ton from 2001 to 2010.
As NASAâs core technology program for all space transportation, the Advanced Space Transportation Program at the Marshall Center is pushing technologies that will dramatically increase the safety and reliability and reduce the cost of space transportation. Today, it costs $10,000 to put a pound of payload in Earth orbit. NASAâs goal is to reduce the cost of getting to space to hundreds of dollars per pound within 25 years and tens of dollars per pound within 40 years. The high cost of space transportation coupled with unreliability is a virtual padlock on the final frontier.