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 master's degree in psychology is a graduate level-degree that generally involves two to three years of study beyond the undergraduate degree. The two most common types of psychology master's degrees are the Master of Arts (M.A.) and the Master of Science (M.S.).