- Historical comet-collision/encounter hypothesis: Buffon, 1749
1749 AD
Buffon’s historical encounter hypothesis
- Single-parent/nebular concept: formation from one parental mass/nebula; distinct from stellar-encounter models.
- Dualistic Concept (Binary Concept): Earth and planets originated due to interaction between the Sun and another celestial body
⚡ Quick Recall
Monistic = one body (Sun alone) involved · Dualistic = two bodies involved
| Hypothesis | Proponent (Year) |
|---|
| Comet/Collision Hypothesis — encounter type | Comte de Buffon (1749) |
| Kant’s Nebular/Cosmogonic Hypothesis — single-parent type | Immanuel Kant (1755) |
| Nebular Hypothesis | Pierre-Simon Laplace (1796); See is associated separately with Capture Theory. |
| Meteoritic Hypothesis — historical model | Lockyer (1890) |
| Planetesimal Hypothesis — encounter type | T.C. Chamberlin and F.R. Moulton (1905) |
⚠ Exam Trap
Laplace (1796): Nebular Hypothesis;
T.J.J. See: separate Capture Theory (1910).
| Hypothesis | Proponent (Year) |
|---|
| Tidal Hypothesis | Jeans: 1916 proposal, major 1919 treatment; Jeffreys: 1929 reworking |
| Double Star Hypothesis | H.N. Russell (Henry Norris Russell) |
| Moon Fission Hypothesis — not a two-star Solar-System model | George Darwin (1879): Moon from rapidly rotating early Earth |
| Supernova Hypothesis | Fred Hoyle; 1946 in the textbook convention used by OP |
| Interstellar Dust Hypothesis | Otto Schmidt (1944): capture/accretion of interstellar matter |
⚡ Quick Recall
Jeans: tidal proposal 1916, major treatment 1919;
Jeffreys: encounter/collision reworking 1929.
- Age: about 4.54 billion years (often rounded to 4.6 billion)
- Method of Determination: Radioactive Dating (1905 AD)
- Rutherford (1905) clearly suggested radioactivity as a tool for measuring geologic time.
| Dating Method | Key Details |
|---|
| Uranium Dating / Lead Dating / Radiometric Dating | Oldest rock • Most important in determining Earth's age |
| Potassium-Argon Method | — |
| Rubidium-Strontium Method | — |
| Uranium-Thorium Method | — |
| Radiocarbon Dating Method | — |
| Chlorine-36 Dating Method | — |
| Carbon Dating (C-14) | Comparatively recent organic remains, generally up to about 50,000 years; not ancient rocks |
⚠ Exam Trap
Uranium/Lead Dating → used for the
oldest rocks (Earth's age); Carbon Dating (C-14) → used for
recent/organic material only — frequently interchanged in MCQs.
- Geometric shape: oblate spheroid; geoid: gravity-based mean-sea-level reference surface
- Slightly flat at top and bottom
| Parameter | Details |
|---|
| Reason for Geoid Shape | Rotation drives the equatorial bulge and polar flattening; gravity defines the geoid and keeps Earth bound. |
| Earth's Mass | 5.97 × 10²⁴ Kg |
| Aquatic Part | 71% |
| Terrestrial Part | 29% |
⚡ Quick Recall
Earth is wider at the Equator and flatter at the poles — Geoid / Flattened (Oblate) Ellipsoid shape.
| Era / Event | Details |
|---|
| Origin period of Humans | African australopithecines and earliest known Homo near the end of the Pliocene |
| Era of Vertebrate Animals | Silurian Period: major early fish/vertebrate diversification |
| Era of Reptiles | Mesozoic Era |
| Age of Dinosaurs | Jurassic Period (~201–145 million years ago): dinosaur diversification/dominance |
⚠ Exam Trap
Mesozoic is an Era (Age of Reptiles);
Jurassic is one Period within it, noted for dinosaur diversification.
| Fact | Details |
|---|
| First Hypothesis of Earth's Origin | Comte de Buffon – 1749 AD |
| Age of Earth | ~4.54 billion years |
| Early 1905 suggestion to use radioactivity for geologic time | Ernest Rutherford (1905 AD) |
| Most important dating method for Earth's age | Uranium / Lead / Radiometric Dating |
| Carbon Dating (C-14) used for | Recent organic remains; generally up to ~50,000 years |
| Shape of Earth | Oblate spheroid (shape); geoid (gravity/mean-sea-level reference) |
| Earth's Mass | 5.97 × 10²⁴ Kg |
| Aquatic vs Terrestrial Part | Aquatic – 71% • Terrestrial – 29% |
| Age of Dinosaurs | Jurassic Period (~201–145 million years ago) |
| Pliocene human-evolution association | African australopithecines; earliest known Homo near Pliocene’s end |
⚡ Quick Recall
Earth’s age:
~4.54 billion years (often rounded to 4.6 billion), estimated using radiometric evidence.