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.
Program in Psychology. Typical doctoral programs in psychology take 5-7 years to complete, though the length of time may vary based on the program and other factors. Most doctoral psychology programs require full-time attendance, and very few are offered online.