Age of the Earth

The Earth is about 4.54 billion years old, formed soon after the birth of the Solar System. This age is calculated primarily by radiometric dating of meteorites, Moon rocks, and the oldest terrestrial minerals (zircons).

To understand Earth’s history in detail, geologists divide this immense span of time into hierarchical units: Eons → Eras → Periods → Epochs. This framework is called the Geological Time Scale (GTS).

Age determining Methods

1. Lord Kelvin’s Cooling Estimate (20–100 Ma) – Inaccurate due to ignorance of radioactive heat.
2. Radiometric Dating (20th century onwards) – Uranium-Lead, Potassium-Argon, and Rubidium-Strontium methods.
3. Evidence Sources – Meteorites (~4.56 Ga), Oldest Earth rocks (~4.0 Ga), Oldest zircons (~4.4 Ga).
4. Final Consensus – Earth’s age is 4.54 ± 0.05 billion years.

Geological Time Scale (Simplified)

Precambrian (≈ 88% of Earth’s history)

• Hadean (4.6–4.0 Ga) – Formation of Earth, Moon, early crust, and oceans.
• Archean (4.0–2.5 Ga) – Stabilization of continental crust, earliest evidence of life (stromatolites).
• Proterozoic (2.5–0.54 Ga) – Oxygenation of atmosphere (Great Oxidation Event), supercontinents (Rodinia).

Phanerozoic (0.54 Ga – Present)

Divided into three Eras:

1. Paleozoic (541–252 Ma)
   • Cambrian Explosion: Rapid diversification of life.
   • Formation of supercontinent Pangaea.
   • Ends with Permian-Triassic extinction (~252 Ma).
2. Mesozoic (252–66 Ma) – “Age of Reptiles”
   • Triassic, Jurassic, Cretaceous periods.
   • Dominance of dinosaurs.
   • Ends with Cretaceous-Paleogene extinction (~66 Ma).
3. Cenozoic (66 Ma – Present) – “Age of Mammals”
   • Paleogene, Neogene, Quaternary periods.
   • Rise of mammals, birds, and finally humans (~2.5 Ma onwards).

Summary

• Age of Earth: 4.54 Ga.
• GTS divides Earth’s history into Precambrian (88%) and Phanerozoic (12%).
• Major events: Formation of crust (Hadean), first life (Archean), oxygen rise (Proterozoic), complex life explosion (Cambrian), dinosaurs (Mesozoic), mammals and humans (Cenozoic).