Back to: Geography of Ethiopia and The Horn – Freshman Courses
Chapter 2: The Geology of Ethiopia and the Horn
Comprehensive Exam Questions
Section A: Multiple Choice (15 Questions)
1. Which era constitutes approximately 88% of Earth’s history and is characterized by the absence of abundant fossils?
A) Paleozoic Era
B) Mesozoic Era
C) Precambrian Era
D) Cenozoic Era
Explanation: As stated in Section 2.3, the Precambrian spans from ~4.5 Ga to ~600 Ma—nearly 5/6 of Earth’s history. Due to metamorphism and lack of well-preserved fossils, it is less understood than the Phanerozoic Eon.
2. The Adigrat Sandstone and Hintalo Limestone were deposited during which geological era?
A) Precambrian
B) Paleozoic
C) Mesozoic
D) Cenozoic
Explanation: Section 2.4.3 explains that during the Mesozoic (~225–70 Ma), a shallow sea transgressed from Somalia, depositing Adigrat Sandstone (early), Hintalo Limestone (peak sea depth), and Upper Sandstone (regression).
3. What caused the formation of the Ethiopian Rift Valley?
A) Volcanic hotspot activity
B) Collision of tectonic plates
C) Divergence of the Nubian and Somali plates
D) Epeirogenic uplift alone
Explanation: Section 2.4.4 states the Rift Valley formed due to tensional forces from plate divergence, causing parallel faulting and subsidence of the central block—a classic example of continental rifting.
4. The Trap Series lavas of the Cenozoic Era primarily formed which major landform?
A) Rift Valley lakes
B) Ethiopian Plateau
C) Afar Depression
D) Blue Nile Gorge
Explanation: Flood basalts (Trap Series) covered Mesozoic sediments during massive epeirogenic uplift (~60 Ma), creating the flat, elevated surface of the Ethiopian Plateau (Section 2.4.4).
5. Which radiometric dating method is most suitable for dating volcanic rocks older than 100,000 years in Ethiopia?
A) Carbon-14
B) Uranium-Lead
C) Potassium-Argon
D) Rubidium-Strontium
Explanation: Section 2.3 notes K-Ar dating (half-life = 1.25 billion years) is “crucial in dating Ethiopian volcanic layers,” including Trap Series lavas and rift volcanism.
6. If a rock contains 25% of its original \(^{40}\text{K}\), and the half-life of \(^{40}\text{K}\) is 1.25 billion years, how old is the rock?
A) 0.625 billion years
B) 1.25 billion years
C) 2.5 billion years
D) 3.75 billion years
Using the decay formula \( N = N_0 (1/2)^{t/T_{1/2}} \), when \( N/N_0 = 0.25 \), two half-lives have passed: \( t = 2 \times 1.25 = 2.5 \) billion years.
7. Which greenstone belt includes the Lega-Dembi gold mine and Kenticha tantalum deposit?
A) Western Belt
B) Southern (Adola) Belt
C) Northern (Tigray) Belt
D) Eastern Belt
Section 2.5.2 states: “The Southern (Adola) greenstone belt: Lega-Dembi, Sakaro… Kenticha Tantalum mine.”
8. The oldest rocks in Ethiopia belong to which geological unit?
A) Mesozoic sedimentary rocks
B) Cenozoic volcanic rocks
C) Precambrian basement complex
D) Quaternary deposits
Section 2.4.1: “Precambrian rocks… form the basement rocks… exposed in northern, western, southern, and eastern Ethiopia.”
9. Which process dominated the Paleozoic Era in Ethiopia?
A) Orogenesis
B) Volcanism
C) Denudation
D) Rifting
Section 2.4.2: “The Paleozoic Era… was dominated by prolonged denudation… reducing mountains to a peneplain.”
10. What is the primary economic significance of the Kenticha Mine?
A) Gold production
B) Platinum extraction
C) Tantalum supply
D) Potash mining
Section 2.5.1: “Kenticha Tantalum mine… Ethiopia presently supplies close to ten percent of the World production of tantalum.”
11. Which of the following is NOT a physiographic subdivision of the Ethiopian Rift Valley?
A) Afar Triangle
B) Main Ethiopian Rift
C) Chew Bahir Rift
D) Ogaden Basin
Section 2.4.4 lists only three subdivisions: Afar Triangle, Main Ethiopian Rift, and Chew Bahir Rift. The Ogaden is a sedimentary basin, not part of the rift system.
12. The Law of Superposition is a principle used in:
A) Absolute dating
B) Relative dating
C) Radiometric decay
D) Seismic analysis
Section 2.3: “Relative dating uses… Law of Superposition: in undisturbed layers, the oldest is at the bottom.”
13. Which mineral resource is most associated with the Precambrian basement rocks of Ethiopia?
A) Coal
B) Gypsum
C) Gold
D) Potash
Section 2.5: “The occurrence of metallic minerals in Ethiopia is associated with the Precambrian rocks… gold, platinum, tantalum.”
14. During which epoch did major rifting of the Ethiopian Rift Valley begin?
A) Paleocene
B) Oligocene–Miocene
C) Pliocene
D) Pleistocene
Section 2.4.4: “Major rifting… began in the Oligocene–Miocene (~30–5 Ma).”
15. Which of the following best describes the Quaternary depositional environment in the Ethiopian Rift?
A) Marine transgression
B) Glacial advance
C) Pluvial lake formation
D) Desert sand dunes
Section 2.4.4: “Heavy Pluvial Rains eroded the plateau… deposited in Rift Valley lakes… forming huge lakes like Ziway-Langano-Shalla.”
Section B: Matching (10 Questions)
Match each term (left) with its correct description (right).
Section C: True/False (5 Questions)
26. The Precambrian basement rocks of Ethiopia are primarily sedimentary in origin.
Answer: False — They are metamorphic and igneous (Section 2.4.1).
27. The Ethiopian Rift Valley is part of the Great East African Rift System that extends to Mozambique.
Answer: True (Section 2.4.4).
28. Carbon-14 dating is commonly used to date the Trap Series lava flows in Ethiopia.
Answer: False — C-14 is too short-lived; K-Ar is used (Section 2.3).
29. The Yubdo area in Wellega is the only active platinum mine in Ethiopia.
Answer: True (Section 2.5.1).
30. The Mesozoic Era was characterized by continuous mountain-building (orogenesis) in Ethiopia.
Answer: False — It was dominated by epeirogenic uplift/subsidence, not orogenesis (Section 2.4.3).
Section D: Define (4 Questions)
31. Half-life
32. Greenstone Belt
33. Peneplain
34. Epeirogenic Movement
Section E: List and Explain (3 Questions)
35. List and explain the three major greenstone belts of Ethiopia and one mineral resource from each.
2. Southern (Adola) Belt: Gold (Lega-Dembi), Tantalum (Kenticha).
3. Northern (Tigray) Belt: Gold (Terakemti), Base metals (Terer).
36. List and explain the three major sedimentary formations of the Mesozoic Era in Ethiopia.
2. Hintalo Limestone: Formed from marine fossils during peak sea depth.
3. Upper Sandstone: Deposited during sea regression as land uplifted.
37. List and explain the three major geologic events of the Cenozoic Era in Ethiopia.
2. Rift Valley Formation: Plate divergence caused faulting and subsidence.
3. Quaternary Volcanism: Renewed eruptions (Erta Ale) and pluvial lake deposition.
Matching Key: 16-a, 17-d, 18-b, 19-c, 20-e, 21-g, 22-f, 23-i, 24-j, 25-k