Final answer:
Interstellar gas clouds have the same basic composition as stars, primarily consisting of hydrogen and helium, and also contain complex molecules similar to those necessary for life.
Step-by-step explanation:
The spectra of interstellar gas clouds show that they have the same basic composition as the most abundant elements in stars, which are hydrogen and helium. About 99% of this interstellar matter is in the form of gas, with individual atoms or molecules primarily consisting of these two elements. Additionally, interstellar gas clouds also contain more complex molecules, including basic building blocks of proteins, indicating similarities in chemical composition to the primordial matter from which stars and planetary systems, including our own, have formed.