Origin and Structure of the Earth – Universe & Solar System

Learning Objectives

At lesson’s end, you should be able to:
- Describe the historical development of theories that explain the origin of the Universe.
- Compare and contrast the major hypotheses explaining the origin of the Solar System.

“What is your idea about the beginning of the Universe?”
- Activates prior knowledge and frames subsequent discussion.

Cosmology: Scientific study of the Universe—its properties, large-scale structure, origin, evolution, and fate.
Universe: Vast expanse containing gas, dust, stars, planets, galaxies, and unknown forms of matter/energy; size and mass are “unimaginable” in human terms.

Observed “redshift” in spectral lines of distant galaxies.
- Redshift definition: Wavelengths from distant objects are displaced toward the red end of the spectrum.
- Quantified by z = \frac{\lambda{\text{observed}}-\lambda{\text{rest}}}{\lambda_{\text{rest}}}.
Interpreted as galaxies moving away from one another → evidence for an expanding Universe.
Empirical relation (Hubble’s Law): v = H_0 d, where
- v = recession velocity (km\,s^{-1}),
- H_0 = Hubble constant ((\approx 70\,\text{km\,s}^{-1}\text{Mpc}^{-1}) in modern estimates),
- d = proper distance (Mpc).
Supported Einstein’s General Relativity prediction that spacetime can expand; overturned the “static, unchanging” Universe once favored by Einstein and earlier astronomers.

Universe created by God; primary documentation in the Bible (Genesis).
Seven Days of Creation (literal interpretation):
- Day 1: Light; separation of light (“day”) from darkness (“night”).
- Day 2: Expanse/firmament separating waters → “sky”.
- Day 3: Dry ground; seas; vegetation.
- Day 4: Sun, moon, stars (to govern day/night and mark times).
- Day 5: Marine life & birds; commanded to multiply.
- Day 6: Land animals; humans (Adam & Eve) “in God’s image” to rule over Earth.
- Day 7: God rests; creation deemed complete.
Philosophical/ethical note: Emphasizes purpose, stewardship, and religious narrative of origin.

Universe undergoes successive cycles:
- Current expansion will eventually halt, reverse (contraction) due to gravitational pull.
- Collapse (“Big Crunch”) followed by another Big Bang.
Significance: Avoids singular “beginning” or “end,” posits an eternal series of cosmic births and deaths.

Universe has always looked essentially the same on large scales; density stays constant despite expansion via continuous creation of matter.
Contrasted with “Evolutionary” models where density decreases over time.
Eventually disfavored because:
- Quasar and CMB observations contradict a truly steady state.

Universe began \sim 13.8\,\text{billion years} ago as an ultra-hot, ultra-dense singular state (< an atom in size).
Key stages:
- Inflation ((<10^{-32}\,\text{s})): Sudden exponential expansion; space filled “instantaneously” with energy and quantum fluctuations.
- Cooling to \sim10^{10}\,\text{K} (within seconds): Fundamental forces (gravity, electromagnetism, strong/weak nuclear) differentiate; matter–antimatter annihilation, slight matter excess remains.
- Nucleosynthesis (first 3 min): Formation of ^1\text{H},\,^2\text{H},\,^3\text{He},\,^4\text{He}.
- Recombination (~380 kyr): At \sim3000\,\text{K} electrons combine with nuclei → neutral atoms; photons decouple → Cosmic Microwave Background (CMB).
- Large-scale structure forms under gravity → galaxies, stars, planets.
Evidence set (beyond Hubble Law):
- CMB radiation (Planck, WMAP).
- Primordial light-element abundances matching Big-Bang nucleosynthesis predictions.
- Large-scale structure simulations.
Philosophical implications: Universe has a finite temporal origin; addresses “creation ex nihilo” debates.

Must explain: nearly circular, coplanar planetary orbits; compositional gradients (rocky inner vs gaseous outer planets); angular momentum distribution; presence of minor bodies.

Initial state: Slowly rotating cloud of gas & dust (solar nebula).
Core mechanisms:
- Self-gravity causes contraction.
- Conservation of angular momentum L = I\omega → as radius shrinks, rotation rate increases.
- Cloud flattens into a disk; central concentration becomes proto-Sun.
- In disk, centrifugal balance + gravitational instabilities form concentric rings → planetesimals → protoplanets → planets.
Modern reinforcement: Observations of protoplanetary disks (e.g., HL Tau) and computer simulations.
Limitations: Early Laplacian picture overproduced angular momentum in proto-Sun; modern variants incorporate magnetic braking, turbulence.

A very young Sun spun so rapidly that equatorial material fissioned off, coalescing into planets.
Supported historically by compositional similarities between Sun and planets.
Issues: Angular momentum calculations and plausible Sun rotation rates render pure fission highly improbable.

Planets formed as solid grains condensed out of a cooling protoplanetary disk, especially in its colder outer regions.
Dust grains → icy/rocky aggregates → kilometer-scale planetesimals → gravitational accretion to planets.
Explains compositional zoning: Higher temperatures near proto-Sun prevented volatile condensation; outer disk retained ices and gases.

Early Solar System filled with myriad small bodies (planetesimals).
Frequent, often violent collisions produced larger bodies:
- Sweeping-up (gravitational focusing) accelerates growth.
- Hypothesis resembles modern “core accretion” plus “giant impacts” (e.g., Theia impact forming Earth’s Moon).
Turbulence in inner disk → higher collision rates → rocky terrestrial planets.
Outer disk collisions gentler → gas-giant cores & icy moons.

Nebular vs Steady-State: Nebular describes local Solar System formation; Steady-State describes cosmic evolution—distinct scales.
Big Bang offers overall cosmic timeline into which nebular processes fit (~9 Gyr after Big Bang, Sun forms).
Creationist narrative provides metaphysical framework; scientific models rely on empirical evidence & falsifiability.

Conservation laws:
- Angular momentum L = mvr = I\omega.
- Energy considerations in gravitational collapse E_g = -\frac{3GM^2}{5R}.
Spectroscopy & redshift relation \Delta \lambda \propto v for non-relativistic velocities.

Understanding cosmic origins informs philosophy, theology, and our perception of humanity’s place in the Universe.
Technological spin-offs: spectroscopy, space-based telescopes, computational physics.
Stewardship themes (Creation story, Day 6) intersect modern environmental ethics.

Primary slide sources:
- slideshare.net/MaryJoyValentino
- slideshare.net/slideshow/origin-of-the-universe-and-the-solar-system/101220905
Textbook chapters on cosmology (Carroll & Ostlie), planet formation (Armitage).
Observation databases: NASA/IPAC Exoplanet Archive for modern “nebula→planet” analogs.

C-O-S-B for Universe theories: Creationist → Oscillating → Steady-State → Big Bang.
N-F-C-C for Solar System: Nebular → Fission → Condensation → Collision.