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.
The majority of students who work on their masterâs degrees in psychology on a full-time basis are able to complete their degrees in approximately two to three years. It will vary depending on the university attended, as some masterâs degree programs require more credit hours than others.