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 PhD, or Doctor of Philosophy, is one of the highest level degrees you can earn in the field of psychology. If you are considering pursuing a graduate degree, you might be wondering how long it takes to earn a PhD in Psychology. Generally, a bachelor's degree takes four years of study.