GEOL 1121 - Origin of Planet Earth (8.20.26)

Composition of the planets

Terrestrial planets - rocky composition w/ a dense iron core

Jupiter + Saturn - gas giants (helium + hydrogen)

Uranus + Neptune - ice giants (frozen water, ammonia, methane)

The Big Bang Theory (Overview)

1. Followed initial cosmic inflation (extremely hot, dense, expanding rapidly)

2. Quarks (elementary particles) collided and formed protons + neutrons (nucleus!)

3. Single protons + surrounding energy (electrons) formed hydrogen!

Big Bang Nucleosynthesis

• Dispersion + collision → some Helium, Lithium, Beryllium, Boron

• → overall composition today reflects these early nuclear reactions

• → 98% H + He (3:1 ratio by mass)

Evidence 1: Speeding away + redshift

• Galaxies speeding away from each other + us

• Based on redshift (electromagnetic radiation)

• Redshift = cosmic Doppler effect

Background radiation (“Cosmic Microwave Backround”)

• Radio telescopes detect electromagnetic radiation in the space between stars and galaxies

• Low-energy radiation = pervasive, uniform in all directions, specific properties predicted by the BBT

Formation of stars: Nebulae and stars

• After the BB, cosmic matter cooled + condensed due to gravity to form nebulae

• Concentrated hydrogen atoms collided + coalesce → rotate and attract more atoms by gravity (a star is born!)

Stellar Nucleosynthesis

Gravitational energy → heats → nuclear fusion reactions (stellar nucleosynthesis!) → Hydrogen, Helium, and release of energy

Stellar nursery

Stars form within clouds of gas and dust known as nebulae

Galaxies

• Clumps of attracted stars

• Rotation = disc shape

Stars as thermonuclear reactors

Lighter elements are fused into heavier ones

Stars (general)

• Range in size, finite lives, spend 95% of existence fusing (“main sequence”)

Death of the star

Fusion into carbon, oxygen, silicon (fusion into heavier and heavier metals because of the ginormous size of heat and mass) → red giant → iron

• Small stars = white dwarf

• Large stars = supernova

• LS: core after nebula may collapse into a neutron star → may collapse into a black hole (if very large)

Cosmic dust + dark matter

Cosmic dust comprises dark matter → planets

Solar Nebula Theory

Cosmic dust collapses + condenses into a rotating sphere to form a new star in the core

• As the sphere spins, it flattens into a disc

• Solar wind radiating frump the star distributes lighter material to the outer edge

Formation of planets

Planetismal → (if big enough) → spherical protoplanet → (if big enough) → melt interior → differentiated (layered) → planet!

The layers of Earth

• Dense core made of iron (and some nickel)

• Mantle (iron-rich silicate rock) - middle of mantle is fluid (asthenosphere)

• Crust → oceanic + continental (crust + upper mantle = lithosphere)