Complex sentence: Beryllium is the chemical element with the symbol Be and atomic number 4, because any beryllium synthesized in stars is short-lived, it is a relatively rare element in both the universe and in the crust of the Earth.
Split into simpler sentences: Beryllium is the chemical element with the symbol Be and atomic number 4. Because any beryllium synthesized in stars is short-lived, it is a relatively rare element in both the universe and in the crust of the Earth.