The solar system formed about 5 billion years ago from a spinning cloud of gas and dust. Gravity caused the core to grow denser and hotter, eventually triggering nuclear fusion and forming the Sun. Lighter gases were pushed outward, leaving heavier materials to form rocky planets near the Sun. In the colder outer regions, ice and gas combined to form gas giants. The solar system is now approximately 4.6 billion years old.

What event marked the birth of our Sun?

• The collapse of a black hole

• The collision of two stars

• The explosion of a supernova

• The initiation of nuclear fusion

What happened to the lighter gases after the Sun was formed?

• They were absorbed by the Sun

• They formed the rocky planets

• They turned into ice

• They were pushed to the outer solar system

What materials primarily formed the rocky planets?

• Ice and gas

• Heavier, rockier materials and metals

• Light gases

• Liquid water

How did the gas giants form in the outer regions of the solar system?

• By the explosion of a nearby star

• Through the evaporation of water

• Through the accumulation of ice and gas

• By the collision of rocky planets

Approximately how old is the solar system?

• 8 billion years

• 6.5 billion years

• 4.6 billion years

• 2.5 billion years