Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object, co-developed between NASA and NSTA, is the fourth of four Science Objects in the Solar System SciPack. It explores the hypothesis that the solar system coalesced out of a giant cloud of gas and debris left in the wake of exploding stars about five billion years ago. Everything in and on the earth, including living organisms, is made of the material from this cloud. As Earth and the other planets formed, the heavier elements fell to their centers. On planets closer to the Sun (the inner planets), the lightest elements and their compounds were mostly blown or boiled away by radiation from the newly formed sun. However, on the outer planets, the lighter substances still surround them as deep atmospheres of gas or as frozen solid layers.