Origin of the Solar System and Earth Lecture Notes

Big Bang Theory:
- Occurred approximately 13.7 billion years ago (13.7 Ga or 13,700,000,000 years).
- Initial conditions: all matter and energy were packed into a point.
Formation of Elements:
- Initially, only lighter elements formed and accumulated in nebulae.
- Cooling allowed for the formation of hydrogen (H) and helium (He) atoms, leading to molecules like H₂.
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Nebula Formation:
- Nebulae are patchy clouds containing approximately 74% hydrogen and 24% helium.
- Formed from the accumulation of elements and molecules and are associated with stellar nucleosynthesis.

Nebula Theory:
- Gravitational collapse of a rotating nebula leads to formation of a disc.
- Inner region collapses to form a protostar; surrounding material becomes planetesimals (around 1 km in size).
- Terrestrial planets (Mercury, Venus, Earth, Mars) form through collisions of planetesimals, while gas giants (Jupiter, Saturn, Uranus, Neptune) accumulate primarily gases.
Solar System Age:
- Estimated to have formed around 4.6 billion years ago (4.6 Ga).

Sun:
- Contains 99.8% of the mass of the Solar System.
Planetary Bodies:
- Planets: Defined as spherical bodies that orbit a star and have cleared their neighboring region of other objects.
- Terrestrial Planets: Mercury, Venus, Earth, Mars - characterized by rocky shells around metallic alloy cores.
- Gas Giants: Jupiter, Saturn, Uranus, Neptune - composed primarily of gases (He, H, ammonia, etc.).
Dwarf Planets:
- For example, Pluto; does not clear its orbital neighborhood and has a significantly smaller size and out-of-plane orbit.

Moons:
- Significant bodies that are locked in orbit around a planet.
Asteroids:
- Located especially between Mars and Jupiter in the asteroid belt; remnants from the formation of the Solar System, approximately 4.6 billion years ago.
- Impacts have been implicated in mass extinction events.
Ice Bodies:
- Comprise clouds and belts, especially beyond Neptune's orbit, can introduce water and organic materials to the inner Solar System.
- Material evaporates and forms tails when these bodies become comets.

Building a Solar System:
- Collapse of a diffuse nebula due to gravity creates two distinct regions: a dense protostar and surrounding rotating disc.
- The evolution from a gas cloud to a star involved temperature and density increases leading to nuclear fusion and creation of heavier elements.
Supernovae:
- Massive stars explode as supernovae, distributing elements necessary for the formation of planets and other bodies of the Solar System.
Stellar Nucleosynthesis:
- Heavier elements formed through the fusion processes in stars and during supernova events (i.e., formation of C, Si, Fe, etc.).

Structure of Atoms:
- Atoms consist of:
- Nucleus containing neutrons (neutral charge) and protons (positive charge).
- An electron cloud surrounding the nucleus (negative charge).
- Elements are defined by the number of protons, which specifies their atomic number.
- Variation in neutron number yields isotopes (e.g., Carbon-12, Carbon-13, Carbon-14).
Stable vs. Radioactive Isotopes:
- Stable isotopes (e.g., Carbon-12, Carbon-13) do not change over time.
- Radioactive isotopes (e.g., Carbon-14) undergo decay into different elements (daughter isotopes).
- Half-Life Concept:
- Defined as the time it takes for half of the parent radioactive isotope to decay into the daughter isotope.
Radiometric Dating:
- Used to determine absolute ages of rocks by measuring parent-to-daughter isotope ratios, for example:
- 14C decays to 14N, half-life is 5730 years.
- 238U decays to 206Pb, half-life is 4.5 billion years.

Giant Impact Hypothesis:
- Proposes that about 4.5 billion years ago, a Mars-sized body impacted the Earth.
- Resulting debris aggregated to form the Moon, while reorienting Earth's rotation and tilt.
Chemical Similarities:
- Chemistry of the Earth and Moon rocks share similarities but are not identical, indicating diverse formation processes.

Habitable Zone:
- Earth is uniquely situated to maintain a hydrosphere and atmosphere, allowing for life.
Active Plate Tectonics:
- Unlike other terrestrial planets, Earth has a dynamic plate tectonic system, influencing geological processes.
Magnetic Field:
- Generated by the geodynamo process, resulting in a molten outer core that protects the planet from solar winds.
- Earth's magnetic field experiences reversals, which can be recorded geologically.

Topics for Further Lectures:
- Development of plate tectonics.
- Formation and composition of the atmosphere.
- Investigation of the hydrosphere's development, critical for sustaining life.