Stratigraphy and Paleontology

[PANTOMATH]

Stratigraphy and Paleontology

1. Geological Time Scale and Fossil Records. 

              The Geological Time Scale (GTS) is a chronological system that divides Earth's history into different time periods based on major geological and biological events. Divisions of the Geological Time Scale The GTS is divided into:

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1. Eons (largest time unit) →
   • Hadean (4.6–4.0 billion years ago) – Formation of Earth.
   • Archean (4.0–2.5 billion years ago) – First life (single-celled organisms).
   • Proterozoic (2.5 billion–541 million years ago) – Oxygen buildup, multicellular life appears.
   • Phanerozoic (541 million years ago–present) – Abundant fossils, complex life.
2. Eras (within eons) →
   • Paleozoic (541–252 million years ago) – First vertebrates, plants, and insects.
   • Mesozoic (252–66 million years ago) – Age of dinosaurs.
   • Cenozoic (66 million years ago–present) – Mammals dominate, humans evolve.
3. Periods & Epochs (smaller subdivisions) →
   • Jurassic Period (Mesozoic Era) – Dinosaurs thrive.
   • Quaternary Period (Cenozoic Era) – Modern humans appear.

Key Point: The GTS is built using rock layers and fossil evidence.

 

B. Fossil Records and Their Importance 
Fossils are remains, impressions, or traces of ancient organisms preserved in rocks.
Types of Fossils

1. Body Fossils – Actual remains like bones, teeth, shells.
2. Trace Fossils – Indirect evidence like footprints, burrows.
3. Microfossils – Tiny fossils (pollen, foraminifera) used in oil exploration.

Importance of Fossils

• Help reconstruct past climates (e.g., coral fossils indicate warm seas).
• Show evolutionary changes over time.
• Provide evidence of extinction events (e.g., dinosaurs).
• Used in biostratigraphy – dating rock layers based on fossil content.

Example: Ammonites (marine fossils) help date Mesozoic rocks.

2. Evolution and Extinction of Prehistoric Species.
Evolution of Life on Earth
Evolution is the gradual change in species over millions of years due to natural selection and genetic variation.
Major Evolutionary Events

1. First Life (3.5 billion years ago) – Bacteria-like organisms in oceans.
2. Cambrian Explosion (541 million years ago) – Rapid rise of diverse life forms.
3. Fish and Amphibians (Paleozoic Era) – First vertebrates appeared.
4. Dinosaurs (Mesozoic Era) – Dominated for 180 million years.
5. Mammals and Birds (Cenozoic Era) – Mammals became dominant after dinosaurs.
6. Humans (2 million years ago–present) – Homo sapiens evolved.

Key Point: Fossils help trace the step-by-step evolution of species.
B. Mass Extinctions (Large-Scale Species Loss)Earth has seen five mass extinctions, where over 75% of species vanished.Major Extinction Events

1. Ordovician-Silurian Extinction (~440 million years ago) – Ice Age killed marine life.
2. Late Devonian Extinction (~375 million years ago) – Loss of coral reefs and marine species.
3. Permian-Triassic Extinction (~252 million years ago) – The largest extinction; 96% of species died.
4. Triassic-Jurassic Extinction (~201 million years ago) – Cleared the way for dinosaurs.
5. Cretaceous-Paleogene Extinction (~66 million years ago) – Dinosaurs wiped out (likely by an asteroid impact).

Example: Chicxulub Crater (Mexico) is linked to the dinosaur extinction.
3. Dating Methods: Radiometric and Relative Dating
To determine the age of rocks and fossils, geologists use two main methods:
A. Relative Dating (Comparing Age Without Exact Numbers)

• Based on stratigraphy (rock layers) – deeper layers are older.
• Uses index fossils (fossils found in specific time periods) for comparison.
• Principles used:
  1. Law of Superposition – Older layers lie below younger layers.
  2. Law of Cross-Cutting Relationships – A fault or intrusion is younger than the rock it cuts.

Example: If a rock layer has trilobite fossils, it belongs to the Paleozoic Era.
B. Radiometric Dating (Finding Absolute Age in Years)

• Uses radioactive decay of elements like carbon-14, uranium-238, and potassium-40.
• Measures the ratio of parent isotopes (unstable) to daughter isotopes (stable).

Common Radiometric Dating Methods

1. Carbon-14 Dating (for fossils <50,000 years old) – Used for bones, wood, and artifacts.
2. Uranium-Lead Dating (for ancient rocks) – Used in Zircon minerals to date Earth’s oldest rocks (~4 billion years).
3. Potassium-Argon Dating (for volcanic rocks >100,000 years old) – Used to date hominid fossils.

Example: Lucy’s fossil (3.2 million years old) was dated using potassium-argon methods.