“We can trace the elements. They were forged in the centers of high-mass stars that went unstable at the ends of their lives, they exploded, scattered their enriched contents across the galaxy, sprinkled into gas clouds that then collapsed and formed stars and planets and life.” EndsScienceStarsPlanetsElementsMassCloudsGasGalaxyUnstableForgedStars And Planets Author:Neil deGrasse Tyson
“Earlier generations of stars in the galaxy could well have had planets. But really, there was only hydrogen and helium to work with, so they'd all be gas giants and not small, rocky planets.” WellsStarsGenerationsPlanetsGiantsGasGalaxyHydrogenHelium Author:Jill Tarter