Final answer:
Interstellar gas clouds have the same basic composition as giant planets like Jupiter and Saturn, primarily composed of hydrogen and helium, indicating a common reservoir of material from the early solar system.
Step-by-step explanation:
The spectra of interstellar gas clouds show that they have the same basic composition as the giant planets like Jupiter and Saturn, which are dominated by hydrogen and helium. These planets, having sufficient gravity, were able to hold on to the lighter gases present during their formation, much like the composition observed in interstellar gas clouds.
This indicates that the gas giants and the interstellar gas clouds likely formed from the same reservoir of material in the early solar system. In stark contrast, terrestrial planets, such as Earth, and our Moon are composed of heavier elements like iron and silicon, and the Moon, as well as the Oort Cloud and the Kuiper Belt objects, show a different composition from that of the interstellar gas clouds.