🌍 Blog 7 – Geological Time Scale & Stratigraphy – DGMS Exam Notes

---

📖 Detailed Notes – Geological Time Scale &Stratigraphy 

                    1️⃣🧭 Introduction 

Understanding geological time scale (GTS) is essential for DGMS geology papers.
It helps mining engineers interpret rock formations, identify mineral-bearing strata, and plan safe mining operations. Geology divides Earth’s 4.6 billion-year history into major Eras, Periods, and Epochs, based on fossil records and rock sequences.
Stratigraphy deals with the study of rock layers and their chronological relationships.

---

🪨 2️⃣ Geological Time Scale (Simplified)

Era	Approx. Age (Million Years)	Dominant Life	Mining Significance
Precambrian	4600 – 570	Algae, bacteria	Oldest rocks, iron & manganese ores
Palaeozoic	570 – 245	Marine life, trilobites	Coal formation starts
Mesozoic	245 – 66	Reptiles, dinosaurs	Petroleum source rocks
Cenozoic	66 – Present	Mammals, humans	Modern mineral deposits

🧩 Mnemonic Tip:
"P-M-M-C" → Precambrian → Palaeozoic → Mesozoic → Cenozoic

---

🧱 3️⃣ Principles of Stratigraphy

1. Law of Superposition:
   Younger rocks lie above older ones (unless disturbed).
   → Used in coal seam correlation.
2. Law of Original Horizontality:
   Sediments are deposited horizontally; folding indicates tectonic disturbance.
3. Law of Faunal Succession:
   Fossil organisms appear in a definite, recognizable order.
4. Uniformitarianism (Hutton’s Principle):
   “Present is the key to the past” — geological processes remain the same over time.

---

⛏️ 4️⃣ Stratigraphic Correlation in Mining Correlation is the process of matching similar rock layers in different locations.

Method	Description	Example
Lithological Correlation	Based on rock type	Sandstone sequence continuity
Palaeontological Correlation	Based on fossils	Gondwana coal seams
Chronological Correlation	Based on radiometric dating	Uranium age dating

DGMS Note:
Accurate correlation is vital for mine planning, borehole logging, and coal seam mapping under CMR 2017 Reg. 128 (Plans and Sections).

---

🌋 5️⃣ Fossils and Their Importance

Fossils are remains or impressions of ancient life preserved in rocks.
Used for:

• Dating rock strata
• Correlating formations
• Identifying past environments

Example:
Glossopteris flora → Gondwana coal-bearing formations (important for DGMS exams).

---

📘 6️⃣ Geological Time Scale Chart (Summary)

Era	Period	Major Life	Rock Record
Precambrian	Archean, Proterozoic	Algae, stromatolites	Old metamorphic & igneous rocks
Palaeozoic	Cambrian–Permian	Trilobites, fishes	Early sedimentary basins
Mesozoic	Triassic–Cretaceous	Reptiles, dinosaurs	Marine & terrestrial sediments
Cenozoic	Tertiary–Quaternary	Mammals, humans	Alluvium, laterite, recent deposits

---

⚡ Quick One-Liners

• Oldest rocks: Archean
• Coal formation: Palaeozoic (Carboniferous)
• Petroleum source rocks: Mesozoic
• Humans evolved: Cenozoic
• Fossils → tools for relative dating
• Principle of superposition → key to stratigraphy
• Glossopteris → Gondwana flora indicator

---

🧾 Descriptive Model Answer 

Q: Explain the significance of geological time scale and stratigraphy in mining.
A:
The geological time scale divides Earth’s history into eras, periods, and epochs, enabling identification of rock age and mineral occurrence. Stratigraphy studies the order and relationship of rock layers.
In mining, it helps locate ore zones, plan mine sections, and correlate seams. Understanding GTS and stratigraphy ensures accurate geological mapping and resource evaluation — key for DGMS exams.

---

🎯 25 DGMS-Style MCQs – Geological Time Scale & Stratigraphy 

Q1. The Earth’s age is approximately:
A. 3.6 billion years
B. 4.6 billion years
C. 5.6 billion years
D. 2.6 billion years
E. 6.0 billion years
Answer: B.
Solution: Radiometric dating methods confirm Earth’s age at around 4.6 billion years.

Q2. Which era is known as the "Age of Reptiles"?
A. Palaeozoic
B. Precambrian
C. Mesozoic
D. Cenozoic
E. Archean
Answer: C.
Solution: The Mesozoic era is dominated by dinosaurs and reptiles.

Q3. The "Law of Superposition" states:
A. Older rocks lie above younger rocks
B. Younger rocks lie above older rocks
C. Rocks are deposited randomly
D. Rocks have no chronological order
E. None of these
Answer: B.
Solution: In undisturbed strata, younger layers overlie older ones.

Q4. Glossopteris fossils are typical of:
A. Cretaceous period
B. Carboniferous period
C. Gondwana formations
D. Jurassic age
E. Devonian age
Answer: C.
Solution: Glossopteris flora is the marker fossil of Gondwana coal formations.

Q5. The principle that “The present is the key to the past” is called:
A. Superposition
B. Uniformitarianism
C. Original Horizontality
D. Faunal Succession
E. Law of Continuity
Answer: B.
Solution: Proposed by James Hutton, Uniformitarianism means geological processes remain constant over time.

Q6. Which of the following is the oldest era?
A. Palaeozoic
B. Mesozoic
C. Cenozoic
D. Precambrian
E. Tertiary
Answer: D.
Solution: Precambrian represents the earliest Earth history.

Q7. The rock layer containing fossils of the same age in different regions can be correlated by:
A. Stratigraphic correlation
B. Lithological correlation
C. Faunal correlation
D. Chemical correlation
E. Radiometric correlation
Answer: C.
Solution: Fossils help correlate strata of similar geological age (faunal succession).

Q8. Which era saw the appearance of the first mammals?
A. Mesozoic
B. Cenozoic
C. Palaeozoic
D. Precambrian
E. None
Answer: A.
Solution: Mammals appeared during late Mesozoic, expanded in Cenozoic.

Q9. The Mesozoic-Cenozoic boundary marks:
A. Start of Ice Age
B. Extinction of dinosaurs
C. Rise of amphibians
D. Volcanic age
E. None
Answer: B.
Solution: The KT boundary (~66 million years ago) marks mass extinction of dinosaurs.

Q10. The study of rock layers and their order is known as:
A. Mineralogy
B. Stratigraphy
C. Petrology
D. Seismology
E. Topography
Answer: B.
Solution: Stratigraphy is the science of rock layering and chronological sequence.

Q11. The term “Chronostratigraphy” refers to:
A. Correlation based on fossils
B. Study of rock color
C. Classification of rocks by age
D. Study of mineral texture
E. Topographical study
Answer: C.
Solution: Chronostratigraphy classifies rocks according to geological time.

Q12. The boundary between Earth’s crust and mantle is known as:
A. Gutenberg Discontinuity
B. Lehmann Discontinuity
C. Mohorovičić Discontinuity
D. Conrad Discontinuity
E. None
Answer: C.
Solution: Moho marks the seismic boundary between crust and mantle.

Q13. In stratigraphy, the “index fossil” is used for:
A. Measuring rock density
B. Dating and correlation
C. Weathering identification
D. Geochemical mapping
E. Mineral grading
Answer: B.
Solution: Index fossils identify and correlate specific time intervals.

Q14. The principle of faunal succession was proposed by:
A. James Hutton
B. Charles Lyell
C. William Smith
D. Charles Darwin
E. Werner
Answer: C.
Solution: William Smith introduced faunal succession using fossils in England.

Q15. Radiometric dating is based on:
A. Decay of radioactive isotopes
B. Layer thickness
C. Fossil abundance
D. Mineral hardness
E. Magnetic field changes
Answer: A.
Solution: Radioactive isotope decay provides absolute rock ages.

Q16. Which rock system in India is richest in coal deposits?
A. Vindhyan
B. Gondwana
C. Cuddapah
D. Dharwar
E. Aravalli
Answer: B.
Solution: Gondwana formations hold major Indian coalfields.

Q17. The youngest rocks in geological history belong to:
A. Archean
B. Proterozoic
C. Mesozoic
D. Cenozoic
E. Cambrian
Answer: D.
Solution: Cenozoic era represents modern deposits and life forms.

Q18. The law stating “Each fossil species has a definite time range” is:
A. Law of Superposition
B. Law of Faunal Succession
C. Law of Continuity
D. Law of Correlation
E. Law of Evolution
Answer: B.
Solution: It defines fossil order through geological history.

Q19. Which of the following fossils indicates marine environment?
A. Trilobite
B. Glossopteris
C. Mammoth
D. Human bones
E. Fern leaves
Answer: A.
Solution: Trilobites are marine arthropods found in early Palaeozoic strata.

Q20. The Gondwana system of rocks is part of which era?
A. Palaeozoic
B. Mesozoic
C. Cenozoic
D. Precambrian
E. None
Answer: A.
Solution: Gondwana belongs to late Carboniferous–early Mesozoic, part of Palaeozoic system.

Q21. Radiometric age determination is most accurate for:
A. Sedimentary rocks
B. Igneous rocks
C. Fossilized shale
D. Coal
E. Limestone
Answer: B.
Solution: Igneous rocks contain radioactive minerals for age dating.

Q22. In DGMS geological mapping, correlation of coal seams is mainly based on:
A. Texture
B. Fossils
C. Lithology & Structure
D. Soil type
E. Vegetation
Answer: C.
Solution: Coal seam correlation uses lithological and structural markers.

Q23. The most common method for determining relative age of strata is:
A. Seismic study
B. Radiometric dating
C. Fossil correlation
D. Chemical analysis
E. GPS mapping
Answer: C.
Solution: Fossil assemblages indicate relative geological time.

Q24. The “Cuddapah system” in India belongs to which type of formation?
A. Recent alluvium
B. Pre-Cambrian sedimentary basin
C. Igneous intrusive
D. Tertiary deposit
E. Metamorphic complex
Answer: B.
Solution: Cuddapah is a Precambrian sedimentary basin, vital in mineral mapping.

Q25. DGMS geological mapping includes stratigraphic details primarily for:
A. Environmental clearance
B. Roof & floor rock stability
C. Mining lease renewal
D. Explosives management
E. Manpower planning
Answer: B.
Solution: Accurate stratigraphy ensures safe support design and hazard prediction.

✅ Conclusion 

Understanding geological time and stratigraphic relationships is vital for mine exploration, drilling, and mapping.
DGMS examinations frequently test eras, principles, and fossil-based correlation questions.
Mastering this topic strengthens conceptual clarity for Management & Legislation (MMLGS) papers.

---

📢 👉 Revise Geology & Mine Planning modules with OnlineMiningExam, India’s 1st Online Mining Academy.
💡 Get topic-wise notes, 100+ tests & video classes.
🌐 Visit: www.onlineminingexam.com | 📞 Call/WhatsApp: 9971114020

---

---