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.
âTo finish a PhD degree takes anywhere from three to five years, sometimes more, depending on the program,â says Dr. Rafael Matos, a graduate of Walden Universityâs online PhD program in psychology. If time and convenience are concerns to you, an online PhD program might be a viable option.