Formation of Our Solar System

1. The Sun, the Earth, and the rest of the Solar System formed from a cloud of gas and dust 4.6 billion years ago.

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• Studies of large numbers of stars and nebulae mean that we understand the life cycle of stars very well.
• The nebula from which our Solar System formed was enriched in elements heavier than hydrogen by earlier generations of stars.

2. Scientists use multiple lines of evidence to determine the age and history of our Solar System. These include physical, geological, and chemical analyses; radiometric dating; studying samples from space; and making observations of other stars and their planetary systems.

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• Some space samples (for example, from comets) provide a pristine record of the primordial material of our Solar System.
• Radiometric dating can be used to determine the age of samples from space, in a similar way to its use in paleontology.

3. Many collisions within the disk of gas and dust surrounding our young Sun built up the planets over a period of a few tens of millions of years.

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• Our Moon probably formed when a Mars-sized body hit the early Earth.
• Late in the formation of the Solar System (but early in its overall history), the Late Heavy Bombardment — a period of enhanced collisions — left a record of cratering on bodies including our Moon.
• We can learn about conditions in the early Solar System by looking at protoplanetary disks around other stars.

4. Collisions between objects in the Solar System continue to take place today.

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5. Earth’s history, including the extinction and evolution of life, was and is influenced by interactions with the rest of the Solar System, such as the impacts of comets and asteroids.

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• The K-Pg extinction, which wiped out the dinosaurs, is thought to have been triggered by an asteroid impact in the Gulf of Mexico.

6. The composition and appearance of the Earth’s surface have been dramatically changed by the presence of life and by geological processes.

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• The presence of life and geological processes have wiped out much of the evidence of past impacts that would otherwise be visible on Earth.