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 doctoral degree is the highest degree you can earn in psychology. A doctorate in psychology typically takes an additional three to seven years to complete, depending on the number of courses taken and the amount of time it takes to finish the dissertation. There are two options for doctorate degrees in psychology, a PhD in psychology or a PsyD.