The planets in our Solar System formed more than 4.6 billion years ago from cloud of dust and gas that collapsed under gravity. Scientists have speculated that this cloud lasted anywhere from 1 to 10 million years, but new research has pegged that period at 2 million years. An international team of researchers studied a variety of meteorites that had formed just before the planets. One group, called calcium aluminum-rich inclusions are known to have formed early in the solar nebula, and others, called chondrules, formed right at the end - 2 million years later.