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 in psychology, after the masterâs is completed, is typically a requirement for most clinical, counseling and research psychologists. Doctorates usually require an additional five to seven years of study plus additional practicums and internships as well as a dissertation.