Notes on Formation of the Universe and Solar System

The Universe, all matter and energy, was created 13.8Ga13.8 \mathrm{Ga} with the Big Bang, which also synthesized H and He. Matter is clumped by gravity, and the Universe continues to expand.

Initially, H and He clumped to form nebulae, which collapsed into the first stars around 13Ga13 \mathrm{Ga}. These 1st generation stars used nuclear fusion to produce elements up to C. When massive stars exhausted their fuel, they exploded as supernovae, creating all 9292 naturally-occurring elements and dispersing them into space. Less massive stars (like our Sun) evolve into red giants and then planetary nebulae.

This cycle repeated, forming 2nd and later generation stars (our Sun being 3rd-5th generation) with these heavier elements. All elements on Earth originated in stars.

Our Solar System, including the Sun and its 8 planets (and Pluto), formed from a nebula 4.6Ga4.6 \mathrm{Ga} (Nebular Theory). This nebula collapsed into the Sun and a protoplanetary disk of volatile (gaseous) and refractory (rocky) materials. Planets grew from dust to planetesimals, then protoplanets, eventually clearing their orbits. These newly formed planets were hot, spherical, and differentiated into layers.

Planetary differences (e.g., terrestrial vs. gas giants) are due to the initial distribution of materials and the solar wind, which moved volatile materials to the outer Solar System.

Key Geologic Dates:

  • Universe forms: 13.8Ga13.8 \mathrm{Ga}

  • Earth & Solar System form: 4.6Ga4.6 \mathrm{Ga}

  • First evidence of life: 3.7Ga3.7 \mathrm{Ga}

  • First dinosaurs: 250Ma250 \mathrm{Ma}

  • Dinosaur extinction: 65Ma65 \mathrm{Ma}

  • Homo sapiens present:  ilde2.0×105yr\ ilde{2.0 \times 10^{5}} \mathrm{yr}