Thus by 1803 there were two known rare earth elements, yttrium and cerium, although it took another 30 years for researchers to determine that other elements were contained in the two ores ceria and yttria (the similarity of the rare earth metals' chemical properties made their separation difficult).
For instance, students who pursue a Ph.D. in psychology usually take from five to seven years depending upon required coursework as well as internship and supervised residency requirements.
A doctorate degree is the highest level of academic degree. Everyone is familiar with the medical doctor, who holds an M.D. (Medical Doctorate). But you can earn a doctorate inalmost any subject area. For example, most states require licensed psychologists to hold a doctorate degree in psychology. Typically a doctorate degree takes four years to complete, post-bachelor's degree.