Supernova remnants are among the most spectacular objects in the galaxy. In 1987, a supernova in the Large Magallenic Cloud, a galaxy 160,000 light-years from Earth, was visible to the naked eye in the night sky of the Southern Hemisphere. The gas and dust that compose supernova remnants expand free of the core and spread out into the galaxy. Many of the radioactive isotopes in the remnant decay to stable elements, creating even more of the heavy elements that exist on Earth. Eventually enough of this gas cools or clumps together with other interstellar gas to begin recollapsing and forming a new generation of stars and planets.
Earth is an especially concentrated residue of a supernova.
Our planet started as gas and dust orbiting the newly forming sun. Lighter elements in our neighborhood, such as hydrogen and helium, were pushed away by the sun, leaving only the heavy stuff created in the massive star and its supernova orbiting and condensing to form the planets Mercury, Venus, Earth, and Mars. If the sun hadn't rid our region of the solar system of the light elements, then Earth would be like Jupiter and the other giants, a planet surrounded by thousands of miles of liquid hydrogen and helium. The stardust I cradled in my arms was warm and soft. Joshua looked up at me with big blue eyes.