Where did we come from? How did the planets, asteroids, comets, and small worlds in our solar system come to be? When did it all happen? These are some of the core questions that drive us to explore other worlds. The below timeline shows some key events that led to our existence on Earth, from the creation of the universe to present day. To learn more, read our Solar System History 101 article.
13.8 billion years ago: The Big Bang forms the universe.
4.6 billion years ago: A group of protostars, one of which will become the Sun, form from a cloud of debris left by prior star explosions in the Milky Way.
4.59 billion years ago: The giant planets Jupiter, Saturn, Uranus, and Neptune form around the protosun. At least Uranus and Neptune form closer to the Sun than where they are today. One or more ice giants may have also formed that were later ejected from the solar system.
4.55 billion years ago: Let there be light: The Sun begins fusing hydrogen into helium.
4.5 to 4.1 billion years ago: The Sun gravitationally separates from its protostar siblings.
4.1 to 3.8 billion years ago: The giant planets' orbits shift, scattering small worlds throughout the solar system. Some bombard the inner planets and likely deliver water and organics to Earth.
4 to 3 billion years ago: Small world bombardment causes widespread volcanism on the inner planets.
3.8 to 3.5 billion years ago: Life begins on Earth.
3 billion years ago: Mars loses most of its atmosphere and water.
2.5 billion years ago: Photosynthetic organisms evolve on Earth and pump oxygen into our atmosphere, helping create the blend of gases we breathe today.
1 billion years ago: Volcanism on the Moon stops.
100 million years ago: An impact on the Moon forms Tycho crater. Saturn gets its rings.
66 million years ago: A giant asteroid impacts Earth, triggering global climate change. Three quarters of life, including the dinosaurs, go extinct.
Now: The solar system is a much calmer place now, though occasional asteroid impacts still threaten Earth.