Our solar system began to take shape about 4.6 billion years ago as the primordial solar nebula of dust and gas began to coalesce around the infant Sun. Within the first billion years or so, the planets formed and life began to emerge on Earth - and perhaps elsewhere.
Many of the current characteristics of the solar system were determined during this critical formative epoch, but because of the tremendous changes that Earth and the planets have undergone over the intervening eons, most physical records have been erased. Our understanding of this period is fragmentary at best.
Fortunately, vital clues are scattered throughout the solar system - from the oldest rocks on the Earth, Earth's Moon, Mars and the asteroids to the frozen outer reaches of the Kuiper Belt, home of the short-period cometsthat may have seeded the planets with the water and other key ingredients for life. Meteoroids that fall to Earth also allow us to look back in time, and to understand the physical setting within which the story of life's origins unfolded.
The formation of the giant planets also had a major effect on the events and processes at work in the early solar system. The gravitational influence of Jupiter in particular governed much of the dynamical behavior that in turn determined many key features of the inner planets.
NASA Solar System Exploration Planetary Database