Planet Earth was born more than 4500 million years ago. It was formed in outer space from a vast cloud of dust and gas. Our Sun and its whole family of nine planets were formed at the same time. Planet Earth is the third out from the Sun and the fifth smallest in size. The Earth began as a gigantic ball of hot gas, much larger than Earth is now. As this ball of gas cooled, it also shrank in size. At last, it cooled, or condensed, into solids and liquids, and began to look more like a planet. But it had no liquid water, only steam. In its early days, the Earth was incredibly hot. Some rocks had formed into their familiar hardness, but others were still red-hot or white-hot liquids. No life was possible on such a hostile world. The Earth was still cooling, but it would be at least 1000 million years before life could begin.