Notes on Universe Formation, Solar System Origin, Earth Formation, and Earth Systems

Universe and Cosmology

  • Universe includes all stars, galaxies, gas and dust, energy, space and time; study called cosmology.

  • Humans describe origin/structure using religion, philosophy, science; current understanding built on previous knowledge and technologies.

  • Theories are tested explanations; not as concrete as laws.

  • Theories of universe origin discussed: Creationism (Genesis), Oscillating Universe, Eternal Inflation/Multiverse, Steady-State, and Big Bang (current model).

Big Bang Theory and Evidence

  • Big Bang: universe originated from an infinitely dense point (singularity) ~13.8 Gyr13.8\,\text{Gyr} ago and has been expanding.

  • Evidence:

    • Redshift: most galaxies move away, stretching light to the red end; supports expansion.

    • Cosmic Microwave Background (CMB): uniform blackbody radiation at ~T≈2.7 KT\approx 2.7\ \text{K}, a relic of early hot universe.

  • Key historical milestones:

    • Lemaitre (1927) proposed expansion from a primeval atom.

    • Hubble (1929) observed galactic redshifts (expanding universe).

    • CMB discovered (1965) by Penzias & Wilson.

Redshift

  • Phenomenon: increase in wavelength of electromagnetic radiation from moving-away sources.

  • Observed in most galaxies moving away, indicating expansion of the universe.

Theories of Universe Origin (Overview)

  • Creation Theory: Genesis narrative of creation in six days; religious origin.

  • Oscillating Universe: universe expands then contracts to a future Big Crunch; linked to positive-curvature GR solutions; introduced by Friedmann (1922) and favored by Einstein at times.

  • Eternal Inflation / Multiverse: after Big Bang, inflation leads to continual creation of other universes; Everett (1957) proposed many-worlds for quantum outcomes.

  • Steady-State Theory: universe infinite in extent and age, looks the same in all directions; no long-term evolution in time (Hoyle, Gold, Bondi, 1948).

  • Big Bang Theory (Current): expansion from a hot, dense state; supported by redshifts, CMB, and elemental abundances.

Timeline and Key Cosmic Milestones

  • Inflation: superfast expansion from ~atomic size to macroscopic scale in a fraction of a second.

  • Post-inflation: hot, dense plasma of particles; cooling allows quarks to form protons/neutrons.

  • Atom formation: electrons combine with protons/neutrons to form mostly H and He.

  • Galaxy formation: gravity leads to clumping forming galaxies.

  • First stars and heavier elements: massive stars fuse elements up to Fe; supernovae seed space with heavier elements.

Formation of the Solar System

  • Solar system may trace to a Big Bang timeline followed by galaxy evolution; solar system age ~4.54 Gyr4.54\,\text{Gyr}, planets formed ~1 Gyr after galaxy formation; meteorites help date the solar system.

Major Theories on Solar System Origin

  • Encounter Hypothesis (Buffon): near-collision with another star tidally pulled material from the Sun to form planets; explains orbital directions and inner-density differences but lacks mechanism for gas contraction.

  • Nebular (Solar Nebula) Hypothesis: gas cloud contracted under self-gravity, forming a rotating disk; central protosun and planets formed within the disk; angular momentum explains disk to planets distribution.

  • Protoplanet Hypothesis: modern refinement of nebular idea; planetesimals formed by accretion in the solar nebula; planets grow from accumulating planetesimals.

Birth of Stars and Primary Energy Source

  • Nuclear Fusion: stars form when contracting gas becomes dense/high-energy; fusion of H into He releases vast energy.

  • First stars formed from H/He gas; heavier elements produced in stellar interiors and supernovae spread through space.

Formation of Planets: From Dust to Worlds

  • Planetesimals: kilometer-sized aggregates formed by accretion; orbiting the proto-Sun.

  • Differentiation: as bodies heat, dense materials (e.g., Fe) sink to cores; lighter materials form crusts/mantles.

  • Iron Catastrophe: core formation driven by melting and sinking of metals; leads to layered planets.

  • Accretion environment: inner Solar System warmer, favors rocky (terrestrial) planets; outer regions cooler, allow gas giants.

Water, Atmosphere, and Habitability of Early Earth

  • Water on Earth: partly from icy comets during accretion; early atmosphere prevents total water loss.

  • Liquid water favored by Earth’s distance from the Sun (Goldilocks zone).

  • 70% of Earth surface is water; 3% freshwater with limited accessible groundwater.

  • Atmosphere initially allowed retention of volatiles; with water present, oceans form and climate stabilizes.

Earth as a Habitable Planet

  • Earth’s habitability factors: plate tectonics, Goldilocks zone location, presence of carbon-based molecules, Moon’s stabilizing influence on rotation and tides.

  • Earth is unique in supporting life as we know it.

Earth's Spheres and Interactions

  • Biosphere: all living organisms; ecosystems; photosynthesis links to carbon/oxygen cycles.

  • Geosphere: solid Earth (crust, mantle, core) including lithosphere and mantle dynamics.

  • Hydrosphere: all water forms (oceans, rivers, groundwater).

  • Atmosphere: gaseous envelope; five layers (troposphere to exosphere); composition around today is ~78% N2, ~21% O2, trace gases.

  • Gaia Hypothesis (Lovelock & Margulis): biosphere acts as a self-regulating system promoting life-sustaining conditions.

Interaction Example: Angat Dam (Earth Spheres Interacting)

  • Hydrosphere: dam stores water for consumption and irrigation.

  • Atmosphere: evaporation occurs; atmospheric water cycles back.

  • Geosphere: construction uses rock/sand/gravel; materials sourced from geosphere.

  • Hydrosphere/Biosphere: downstream water supports life and human needs; groundwater interactions occur.

Geology and Internal Structure of the Earth

  • Lithosphere: rigid outer shell composed of crust + upper mantle; ~100 km100\ \text{km} thick; brittle, breaks during earthquakes.

  • Asthenosphere: ductile, flowing layer beneath lithosphere; lithosphere rides on it.

  • Mantle: ~2900 km2900\ \text{km} thick; iron/magnesium-rich; divided into upper and lower mantle.

  • Core: center of Earth; outer core is liquid, inner core is solid; outer core generates magnetic field; temperatures up to ~5×104 ∘C5\times 10^4\ ^\circ\text{C}.

  • Transition Discontinuities: boundaries between crust/mantle and core regions (Conrad, Moho, Repetti, Gutenberg, Lehmann).

    • Moho: crust-mantle boundary.

    • Gutenberg: mantle-core boundary.

    • Lehmann: outer-inner core boundary.

    • Repetti: upper-lower mantle boundary.

    • Conrad: crust-upper mantle boundary.

Layers of the Earth and Crust Types

  • Crust: outermost solid shell; two types:

    • Oceanic crust: denser, basaltic, ~5−10 km5-10\ \text{km} thick; part of lithosphere.

    • Continental crust: less dense, granitic, ~30−50 km30-50\ \text{km} thick; older.

  • Mantle and Core: beneath crust; upper mantle together with crust forms lithosphere; asthenosphere beneath lithosphere.

Plate Tectonics and Structure

  • Lithosphere plates float on the asthenosphere; interactions cause earthquakes and volcanism.

  • Accretionary processes and subduction zones shape continents and oceans.

Atmospheric and Hydrospheric Layers

  • Atmosphere: troposphere, stratosphere, mesosphere, thermosphere, exosphere.

  • Hydrosphere: covers ~71% of Earth; oceans ~97% of all water; freshwater ~3% (most locked as ice; limited accessible groundwater).

  • Water cycle connects atmosphere, hydrosphere, biosphere, and lithosphere.

Biogeochemical Cycles

  • Biogeochemical cycles move elements through non-living reservoirs and living systems.

  • Major cycles covered:

    • Water Cycle: evaporation, transpiration, condensation, precipitation, infiltration, surface runoff, groundwater flow.

    • Carbon Cycle: photosynthesis, respiration, decomposition, fossil fuels, combustion; carbon moves between atmosphere, biosphere, hydrosphere, and geosphere.

    • Nitrogen Cycle: nitrogen fixation, nitrification, assimilation, ammonification, denitrification; essential for amino acids, nucleic acids, chlorophyll.

    • Oxygen Cycle: photolysis produces O2, ozone formation, respiration, photosynthesis; maintains atmospheric O2 balance.

Quick Reference Facts (Key Figures)

  • Universe age: ≈13.8 Gyr\approx 13.8\ \text{Gyr}; Solar System age: ≈4.54 Gyr\approx 4.54\ \text{Gyr}.

  • CMB temperature: T≈2.7 KT \approx 2.7\ \text{K}.

  • Lithosphere thickness: ~100 km100\ \text{km}.

  • Outer core temperature: up to ~5×104 ∘C5\times 10^4\ ^\circ\text{C}.

  • Water on Earth: ~70%70\% surface coverage; freshwater ~3%3\% of total water; accessible groundwater only a portion of that.

Note on Habitable Conditions

  • The Goldilocks zone is the region around a star where planetary surface conditions can sustain liquid water.

  • Magnetic field (outer core) and atmosphere help protect surface water and enable long-term habitability.

Key Questions to Remember

  • What evidence supports the Big Bang over steady-state models? (Redshift, CMB, element abundances)

  • How does differentiation create Earth's layered structure (crust, mantle, core)?

  • What roles do the biosphere, atmosphere, hydrosphere, and lithosphere play in habitability and geochemical cycles?

  • How do giant-scale cycles (water, carbon, nitrogen, oxygen) connect living and non-living reservoirs?